[PATCH v1 0/8] Remove device private pages from physical address space

[PATCH v1 0/8] Remove device private pages from physical address space

[Jordan Niethe]

Today, when creating these device private struct pages, the first step
is to use request_free_mem_region() to get a range of physical address
space large enough to represent the devices memory. This allocated
physical address range is then remapped as device private memory using
memremap_pages.

Needing allocation of physical address space has some problems:

  1) There may be insufficient physical address space to represent the
     device memory. KASLR reducing the physical address space and VM
     configurations with limited physical address space increase the
     likelihood of hitting this especially as device memory increases. This
     has been observed to prevent device private from being initialized.  

  2) Attempting to add the device private pages to the linear map at
     addresses beyond the actual physical memory causes issues on
     architectures like aarch64  - meaning the feature does not work there [0].

This series changes device private memory so that it does not require
allocation of physical address space and these problems are avoided.
Instead of using the physical address space, we introduce a "device
private address space" and allocate from there.

A consequence of placing the device private pages outside of the
physical address space is that they no longer have a PFN. However, it is
still necessary to be able to look up a corresponding device private
page from a device private PTE entry, which means that we still require
some way to index into this device private address space. Instead of a
PFN, device private pages use an offset into this device private address
space to look up device private struct pages.

The problem that then needs to be addressed is how to avoid confusing
these device private offsets with PFNs. It is the inherent limited usage
of the device private pages themselves which make this possible. A
device private page is only used for userspace mappings, we do not need
to be concerned with them being used within the mm more broadly. This
means that the only way that the core kernel looks up these pages is via
the page table, where their PTE already indicates if they refer to a
device private page via their swap type, e.g.  SWP_DEVICE_WRITE. We can
use this information to determine if the PTE contains a PFN which should
be looked up in the page map, or a device private offset which should be
looked up elsewhere.

This applies when we are creating PTE entries for device private pages -
because they have their own type there are already must be handled
separately, so it is a small step to convert them to a device private
PFN now too.

The first part of the series updates callers where device private
offsets might now be encountered to track this extra state.

The last patch contains the bulk of the work where we change how we
convert between device private pages to device private offsets and then
use a new interface for allocating device private pages without the need
for reserving physical address space.

By removing the device private pages from the physical address space,
this series also opens up the possibility to moving away from tracking
device private memory using struct pages in the future. This is
desirable as on systems with large amounts of memory these device
private struct pages use a signifiant amount of memory and take a
significant amount of time to initialize.

Changes in v1:
  - mm/migrate_device: Add migrate PFN flag to track device private pages
    - Update for HMM huge page support
    - Update existing drivers to use MIGRATE_PFN_DEVICE

  - mm/page_vma_mapped: Add flags to page_vma_mapped_walk::pfn to track
    device private pages
    - Update for HMM huge page support 

  - mm: Add helpers to create migration entries from struct pages
    - New to series

  - mm: Add a new swap type for migration entries of device private pages
    - Update for softleaf infrastructure
    - Handle make_readable_migration_entry_from_page() and friends

  - mm: Add helpers to create device private entries from struct pages
    - New to series

  - mm/hmm: Add flag to track device private pages
    - Update HMM_PFN_ORDER_SHIFT
    - Handle hmm_vma_handle_absent_pmd()

  - mm: Remove device private pages from the physical address space
    - Include NUMA node paramater for memremap_device_private_pagemap()
    - Add devm_memremap_device_private_pagemap() and friends
    - Update existing users of memremap_pages():
      - ppc ultravisor
      - drm/amd/amdkfd
      - gpu/drm/xe
      - gpu/drm/nouveau
    - Update for HMM huge page support

Testing:
- selftests/mm/hmm-tests on an amd64 VM

* NOTE: I will need help in testing the driver changes *

Revisions:
- RFC: https://lore.kernel.org/all/20251128044146.80050-1-jniethe@nvidia.com/

[0] https://lore.kernel.org/lkml/CAMj1kXFZ=4hLL1w6iCV5O5uVoVLHAJbc0rr40j24ObenAjXe9w@mail.gmail.com/

Jordan Niethe (8):
  mm/migrate_device: Add migrate PFN flag to track device private pages
  mm/page_vma_mapped: Add flags to page_vma_mapped_walk::pfn to track
    device private pages
  mm: Add helpers to create migration entries from struct pages
  mm: Add a new swap type for migration entries of device private pages
  mm: Add helpers to create device private entries from struct pages
  mm/util: Add flag to track device private pages in page snapshots
  mm/hmm: Add flag to track device private pages
  mm: Remove device private pages from the physical address space

 Documentation/mm/hmm.rst                 |  11 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c       |  43 ++---
 drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  32 ++--
 drivers/gpu/drm/drm_pagemap.c            |   4 +-
 drivers/gpu/drm/nouveau/nouveau_dmem.c   |  37 ++---
 drivers/gpu/drm/xe/xe_svm.c              |  28 +---
 fs/proc/page.c                           |   6 +-
 include/linux/hmm.h                      |   7 +-
 include/linux/leafops.h                  |  86 ++++++++--
 include/linux/memremap.h                 |  64 +++++++-
 include/linux/migrate.h                  |   5 +
 include/linux/mm.h                       |   9 +-
 include/linux/rmap.h                     |  33 +++-
 include/linux/swap.h                     |   8 +-
 include/linux/swapops.h                  | 124 +++++++++++++++
 lib/test_hmm.c                           |  73 +++++----
 mm/debug.c                               |   9 +-
 mm/hmm.c                                 |   5 +-
 mm/huge_memory.c                         |  53 ++++---
 mm/memory.c                              |  14 +-
 mm/memremap.c                            | 193 ++++++++++++++++++-----
 mm/migrate.c                             |   6 +-
 mm/migrate_device.c                      |  45 +++---
 mm/mm_init.c                             |   8 +-
 mm/mprotect.c                            |  21 ++-
 mm/page_vma_mapped.c                     |  32 +++-
 mm/rmap.c                                |  59 ++++---
 mm/util.c                                |   8 +-
 mm/vmscan.c                              |   2 +-
 29 files changed, 737 insertions(+), 288 deletions(-)


base-commit: f8f9c1f4d0c7a64600e2ca312dec824a0bc2f1da
-- 
2.34.1

[PATCH v1 1/8] mm/migrate_device: Add migrate PFN flag to track device private pages

[Jordan Niethe]

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have
normal PFN and must be handled separately.

Prepare for this by adding a MIGRATE_PFN_DEVICE flag to indicate
that a migrate pfn contains a PFN for a device private page.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>

---
v1:
- Update for HMM huge page support
- Update existing drivers to use MIGRATE_PFN_DEVICE
---
 arch/powerpc/kvm/book3s_hv_uvmem.c       |  2 +-
 drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  3 ++-
 drivers/gpu/drm/drm_pagemap.c            |  2 +-
 drivers/gpu/drm/nouveau/nouveau_dmem.c   |  2 +-
 include/linux/migrate.h                  |  1 +
 lib/test_hmm.c                           |  4 ++--
 mm/migrate_device.c                      | 11 ++++++++---
 7 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index e5000bef90f2..dac5d6454920 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -784,7 +784,7 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma,
 		}
 	}
 
-	*mig.dst = migrate_pfn(page_to_pfn(dpage));
+	*mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
 	migrate_vma_pages(&mig);
 out_finalize:
 	migrate_vma_finalize(&mig);
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
index af53e796ea1b..0257c6e7f680 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -303,7 +303,8 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,
 			dst[i] = cursor.start + (j << PAGE_SHIFT);
 			migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);
 			svm_migrate_get_vram_page(prange, migrate->dst[i]);
-			migrate->dst[i] = migrate_pfn(migrate->dst[i]);
+			migrate->dst[i] = migrate_pfn(migrate->dst[i]) |
+					  MIGRATE_PFN_DEVICE;
 			mpages++;
 		}
 		spage = migrate_pfn_to_page(migrate->src[i]);
diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
index 37d7cfbbb3e8..0c756d73419f 100644
--- a/drivers/gpu/drm/drm_pagemap.c
+++ b/drivers/gpu/drm/drm_pagemap.c
@@ -404,7 +404,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 		struct page *page = pfn_to_page(migrate.dst[i]);
 
 		pages[i] = page;
-		migrate.dst[i] = migrate_pfn(migrate.dst[i]);
+		migrate.dst[i] = migrate_pfn(migrate.dst[i]) | MIGRATE_PFN_DEVICE;
 		drm_pagemap_get_devmem_page(page, zdd);
 	}
 
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 58071652679d..2bd80c6f5bcd 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -766,7 +766,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
 		((paddr >> PAGE_SHIFT) << NVIF_VMM_PFNMAP_V0_ADDR_SHIFT);
 	if (src & MIGRATE_PFN_WRITE)
 		*pfn |= NVIF_VMM_PFNMAP_V0_W;
-	mpfn = migrate_pfn(page_to_pfn(dpage));
+	mpfn = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
 	if (folio_order(page_folio(dpage)))
 		mpfn |= MIGRATE_PFN_COMPOUND;
 	return mpfn;
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 26ca00c325d9..52f65cd5c932 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -126,6 +126,7 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
 #define MIGRATE_PFN_MIGRATE	(1UL << 1)
 #define MIGRATE_PFN_WRITE	(1UL << 3)
 #define MIGRATE_PFN_COMPOUND	(1UL << 4)
+#define MIGRATE_PFN_DEVICE	(1UL << 5)
 #define MIGRATE_PFN_SHIFT	6
 
 static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 8af169d3873a..19681904a666 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -727,7 +727,7 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 				rpage = BACKING_PAGE(dpage);
 				rpage->zone_device_data = dmirror;
 
-				*dst = migrate_pfn(page_to_pfn(dpage)) | write;
+				*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;
 				src_page = pfn_to_page(spfn + i);
 
 				if (spage)
@@ -754,7 +754,7 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 		pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
 			 page_to_pfn(spage), page_to_pfn(dpage));
 
-		*dst = migrate_pfn(page_to_pfn(dpage)) | write;
+		*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;
 
 		if (is_large) {
 			int i;
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 23379663b1e1..5d108ddf1a97 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -199,6 +199,7 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
 		(migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) &&
 		(IS_ALIGNED(start, HPAGE_PMD_SIZE) &&
 		 IS_ALIGNED(end, HPAGE_PMD_SIZE))) {
+		unsigned long device_private = 0;
 
 		struct page_vma_mapped_walk pvmw = {
 			.ptl = ptl,
@@ -208,10 +209,13 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
 		};
 
 		unsigned long pfn = page_to_pfn(folio_page(folio, 0));
+		if (folio_is_device_private(folio))
+			device_private = MIGRATE_PFN_DEVICE;
 
 		migrate->src[migrate->npages] = migrate_pfn(pfn) | write
 						| MIGRATE_PFN_MIGRATE
-						| MIGRATE_PFN_COMPOUND;
+						| MIGRATE_PFN_COMPOUND
+						| device_private;
 		migrate->dst[migrate->npages++] = 0;
 		migrate->cpages++;
 		ret = set_pmd_migration_entry(&pvmw, folio_page(folio, 0));
@@ -329,7 +333,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 			}
 
 			mpfn = migrate_pfn(page_to_pfn(page)) |
-					MIGRATE_PFN_MIGRATE;
+					MIGRATE_PFN_MIGRATE |
+					MIGRATE_PFN_DEVICE;
 			if (softleaf_is_device_private_write(entry))
 				mpfn |= MIGRATE_PFN_WRITE;
 		} else {
@@ -1368,7 +1373,7 @@ static unsigned long migrate_device_pfn_lock(unsigned long pfn)
 		return 0;
 	}
 
-	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
+	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE | MIGRATE_PFN_DEVICE;
 }
 
 /**
-- 
2.34.1

[PATCH v1 2/8] mm/page_vma_mapped: Add flags to page_vma_mapped_walk::pfn to track device private pages

[Jordan Niethe]

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have
normal PFN and must be handled separately.

Prepare for this by modifying page_vma_mapped_walk::pfn to contain flags
as well as a PFN. Introduce a PVMW_PFN_DEVICE_PRIVATE flag to indicate
that a page_vma_mapped_walk::pfn contains a PFN for a device private
page.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
v1:
  - Update for HMM huge page support
---
 include/linux/rmap.h | 30 +++++++++++++++++++++++++++++-
 mm/page_vma_mapped.c | 18 ++++++++++--------
 mm/rmap.c            |  4 ++--
 mm/vmscan.c          |  2 +-
 4 files changed, 42 insertions(+), 12 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index daa92a58585d..57c63b6a8f65 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -939,9 +939,37 @@ struct page_vma_mapped_walk {
 	unsigned int flags;
 };
 
+/* pfn is a device private offset */
+#define PVMW_PFN_DEVICE_PRIVATE	(1UL << 0)
+#define PVMW_PFN_SHIFT		1
+
+static inline unsigned long page_vma_walk_pfn(unsigned long pfn)
+{
+	return (pfn << PVMW_PFN_SHIFT);
+}
+
+static inline unsigned long folio_page_vma_walk_pfn(const struct folio *folio)
+{
+	if (folio_is_device_private(folio))
+		return page_vma_walk_pfn(folio_pfn(folio)) |
+		       PVMW_PFN_DEVICE_PRIVATE;
+
+	return page_vma_walk_pfn(folio_pfn(folio));
+}
+
+static inline struct page *page_vma_walk_pfn_to_page(unsigned long pvmw_pfn)
+{
+	return pfn_to_page(pvmw_pfn >> PVMW_PFN_SHIFT);
+}
+
+static inline struct folio *page_vma_walk_pfn_to_folio(unsigned long pvmw_pfn)
+{
+	return page_folio(page_vma_walk_pfn_to_page(pvmw_pfn));
+}
+
 #define DEFINE_FOLIO_VMA_WALK(name, _folio, _vma, _address, _flags)	\
 	struct page_vma_mapped_walk name = {				\
-		.pfn = folio_pfn(_folio),				\
+		.pfn = folio_page_vma_walk_pfn(_folio),			\
 		.nr_pages = folio_nr_pages(_folio),			\
 		.pgoff = folio_pgoff(_folio),				\
 		.vma = _vma,						\
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index b38a1d00c971..7fddafed3ebb 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -129,19 +129,19 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 		pfn = softleaf_to_pfn(entry);
 	}
 
-	if ((pfn + pte_nr - 1) < pvmw->pfn)
+	if ((pfn + pte_nr - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
 		return false;
-	if (pfn > (pvmw->pfn + pvmw->nr_pages - 1))
+	if (pfn > ((pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1))
 		return false;
 	return true;
 }
 
 /* Returns true if the two ranges overlap.  Careful to not overflow. */
-static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
+static bool check_pmd(unsigned long pfn, bool device_private, struct page_vma_mapped_walk *pvmw)
 {
-	if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
+	if ((pfn + HPAGE_PMD_NR - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
 		return false;
-	if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
+	if (pfn > (pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1)
 		return false;
 	return true;
 }
@@ -254,14 +254,16 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 				entry = softleaf_from_pmd(pmde);
 
 				if (!softleaf_is_migration(entry) ||
-				    !check_pmd(softleaf_to_pfn(entry), pvmw))
+				    !check_pmd(softleaf_to_pfn(entry),
+					       softleaf_is_device_private(entry),
+					       pvmw))
 					return not_found(pvmw);
 				return true;
 			}
 			if (likely(pmd_trans_huge(pmde))) {
 				if (pvmw->flags & PVMW_MIGRATION)
 					return not_found(pvmw);
-				if (!check_pmd(pmd_pfn(pmde), pvmw))
+				if (!check_pmd(pmd_pfn(pmde), false, pvmw))
 					return not_found(pvmw);
 				return true;
 			}
@@ -350,7 +352,7 @@ unsigned long page_mapped_in_vma(const struct page *page,
 {
 	const struct folio *folio = page_folio(page);
 	struct page_vma_mapped_walk pvmw = {
-		.pfn = page_to_pfn(page),
+		.pfn = folio_page_vma_walk_pfn(folio),
 		.nr_pages = 1,
 		.vma = vma,
 		.flags = PVMW_SYNC,
diff --git a/mm/rmap.c b/mm/rmap.c
index f955f02d570e..79a2478b4aa9 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1112,7 +1112,7 @@ static bool mapping_wrprotect_range_one(struct folio *folio,
 {
 	struct wrprotect_file_state *state = (struct wrprotect_file_state *)arg;
 	struct page_vma_mapped_walk pvmw = {
-		.pfn		= state->pfn,
+		.pfn		= page_vma_walk_pfn(state->pfn),
 		.nr_pages	= state->nr_pages,
 		.pgoff		= state->pgoff,
 		.vma		= vma,
@@ -1190,7 +1190,7 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
 		      struct vm_area_struct *vma)
 {
 	struct page_vma_mapped_walk pvmw = {
-		.pfn		= pfn,
+		.pfn		= page_vma_walk_pfn(pfn),
 		.nr_pages	= nr_pages,
 		.pgoff		= pgoff,
 		.vma		= vma,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 670fe9fae5ba..be5682d345b5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4203,7 +4203,7 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	pte_t *pte = pvmw->pte;
 	unsigned long addr = pvmw->address;
 	struct vm_area_struct *vma = pvmw->vma;
-	struct folio *folio = pfn_folio(pvmw->pfn);
+	struct folio *folio = page_vma_walk_pfn_to_folio(pvmw->pfn);
 	struct mem_cgroup *memcg = folio_memcg(folio);
 	struct pglist_data *pgdat = folio_pgdat(folio);
 	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
-- 
2.34.1

[PATCH v1 3/8] mm: Add helpers to create migration entries from struct pages

[Jordan Niethe]

To create a new migration entry for a given struct page, that page is
first converted to its pfn, before passing the pfn to
make_readable_migration_entry() (and friends).

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have a
pfn and must be handled separately.

Prepare for this with a new set of helpers:

  - make_readable_migration_entry_from_page()
  - make_readable_exclusive_migration_entry_from_page()
  - make_writable_migration_entry_from_page()

These helpers take a struct page as parameter instead of a pfn. This
will allow more flexibility for handling the swap offset field
differently for device private pages.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
---
v1:
  - New to series
---
 include/linux/swapops.h | 25 +++++++++++++++++++++++++
 mm/huge_memory.c        | 18 +++++++++---------
 mm/migrate_device.c     | 12 ++++++------
 mm/rmap.c               | 12 ++++++------
 4 files changed, 46 insertions(+), 21 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 8cfc966eae48..72aa636fdb48 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -173,16 +173,31 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 	return swp_entry(SWP_MIGRATION_READ, offset);
 }
 
+static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_READ, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, offset);
 }
 
+static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_MIGRATION_WRITE, offset);
 }
 
+static inline swp_entry_t make_writable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_MIGRATION_WRITE, page_to_pfn(page));
+}
+
 /*
  * Returns whether the host has large enough swap offset field to support
  * carrying over pgtable A/D bits for page migrations.  The result is
@@ -222,11 +237,21 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 40cf59301c21..08c68e2e3f06 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3183,14 +3183,14 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 		for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
 			if (write)
-				swp_entry = make_writable_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_writable_migration_entry_from_page(
+							page + i);
 			else if (anon_exclusive)
-				swp_entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_readable_exclusive_migration_entry_from_page(
+							page + i);
 			else
-				swp_entry = make_readable_migration_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_readable_migration_entry_from_page(
+							page + i);
 			if (young)
 				swp_entry = make_migration_entry_young(swp_entry);
 			if (dirty)
@@ -4890,11 +4890,11 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
 	if (pmd_dirty(pmdval))
 		folio_mark_dirty(folio);
 	if (pmd_write(pmdval))
-		entry = make_writable_migration_entry(page_to_pfn(page));
+		entry = make_writable_migration_entry_from_page(page);
 	else if (anon_exclusive)
-		entry = make_readable_exclusive_migration_entry(page_to_pfn(page));
+		entry = make_readable_exclusive_migration_entry_from_page(page);
 	else
-		entry = make_readable_migration_entry(page_to_pfn(page));
+		entry = make_readable_migration_entry_from_page(page);
 	if (pmd_young(pmdval))
 		entry = make_migration_entry_young(entry);
 	if (pmd_dirty(pmdval))
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 5d108ddf1a97..7eef21d63364 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -438,14 +438,14 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 
 			/* Setup special migration page table entry */
 			if (mpfn & MIGRATE_PFN_WRITE)
-				entry = make_writable_migration_entry(
-							page_to_pfn(page));
+				entry = make_writable_migration_entry_from_page(
+							page);
 			else if (anon_exclusive)
-				entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(page));
+				entry = make_readable_exclusive_migration_entry_from_page(
+							page);
 			else
-				entry = make_readable_migration_entry(
-							page_to_pfn(page));
+				entry = make_readable_migration_entry_from_page(
+							page);
 			if (pte_present(pte)) {
 				if (pte_young(pte))
 					entry = make_migration_entry_young(entry);
diff --git a/mm/rmap.c b/mm/rmap.c
index 79a2478b4aa9..bb881b0c4b06 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2539,14 +2539,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			 * pte is removed and then restart fault handling.
 			 */
 			if (writable)
-				entry = make_writable_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_writable_migration_entry_from_page(
+							subpage);
 			else if (anon_exclusive)
-				entry = make_readable_exclusive_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_readable_exclusive_migration_entry_from_page(
+							subpage);
 			else
-				entry = make_readable_migration_entry(
-							page_to_pfn(subpage));
+				entry = make_readable_migration_entry_from_page(
+							subpage);
 			if (likely(pte_present(pteval))) {
 				if (pte_young(pteval))
 					entry = make_migration_entry_young(entry);
-- 
2.34.1

[PATCH v1 4/8] mm: Add a new swap type for migration entries of device private pages

[Jordan Niethe]

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have
pfns and must be handled separately.

When migrating a device private page a migration entry is created for
that page - this includes the pfn for that page. Once device private
pages begin using device memory offsets instead of pfns we will need to
be able to determine which kind of value is in the entry so we can
associate it with the correct page.

Introduce new swap types:

  - SWP_MIGRATION_DEVICE_READ
  - SWP_MIGRATION_DEVICE_WRITE
  - SWP_MIGRATION_DEVICE_READ_EXCLUSIVE

These correspond to

  - SWP_MIGRATION_READ
  - SWP_MIGRATION_WRITE
  - SWP_MIGRATION_READ_EXCLUSIVE

except the swap entry contains a device private offset.

The existing helpers such as is_writable_migration_entry() will still
return true for a SWP_MIGRATION_DEVICE_WRITE entry.

Introduce new helpers such as
is_writable_device_migration_private_entry() to disambiguate between a
SWP_MIGRATION_WRITE and a SWP_MIGRATION_DEVICE_WRITE entry.

Introduce corresponding softleaf types and helpers.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
v1:
  - Update for softleaf infrastructure
  - Handle make_readable_migration_entry_from_page() and friends
  - s/make_device_migration_readable_exclusive_migration_entry/make_readable_exclusive_migration_device_private_entry
  - s/is_device_migration_readable_exclusive_entry/is_readable_exclusive_device_private_migration_entry/
---
 include/linux/leafops.h | 70 +++++++++++++++++++++++++++++++++----
 include/linux/swap.h    |  8 ++++-
 include/linux/swapops.h | 76 +++++++++++++++++++++++++++++++++++++++++
 mm/huge_memory.c        | 21 +++++++++---
 mm/memory.c             | 10 ++++--
 mm/mprotect.c           | 21 +++++++++---
 mm/page_vma_mapped.c    |  3 +-
 7 files changed, 188 insertions(+), 21 deletions(-)

diff --git a/include/linux/leafops.h b/include/linux/leafops.h
index cfafe7a5e7b1..a4a5c3ad647b 100644
--- a/include/linux/leafops.h
+++ b/include/linux/leafops.h
@@ -28,6 +28,9 @@ enum softleaf_type {
 	SOFTLEAF_DEVICE_PRIVATE_READ,
 	SOFTLEAF_DEVICE_PRIVATE_WRITE,
 	SOFTLEAF_DEVICE_EXCLUSIVE,
+	SOFTLEAF_MIGRATION_DEVICE_READ,
+	SOFTLEAF_MIGRATION_DEVICE_READ_EXCLUSIVE,
+	SOFTLEAF_MIGRATION_DEVICE_WRITE,
 	/* H/W posion types. */
 	SOFTLEAF_HWPOISON,
 	/* Marker types. */
@@ -165,6 +168,12 @@ static inline enum softleaf_type softleaf_type(softleaf_t entry)
 		return SOFTLEAF_DEVICE_PRIVATE_READ;
 	case SWP_DEVICE_EXCLUSIVE:
 		return SOFTLEAF_DEVICE_EXCLUSIVE;
+	case SWP_MIGRATION_DEVICE_READ:
+		return SOFTLEAF_MIGRATION_DEVICE_READ;
+	case SWP_MIGRATION_DEVICE_WRITE:
+		return SOFTLEAF_MIGRATION_DEVICE_WRITE;
+	case SWP_MIGRATION_DEVICE_READ_EXCLUSIVE:
+		return SOFTLEAF_MIGRATION_DEVICE_READ_EXCLUSIVE;
 #endif
 #ifdef CONFIG_MEMORY_FAILURE
 	case SWP_HWPOISON:
@@ -190,16 +199,62 @@ static inline bool softleaf_is_swap(softleaf_t entry)
 	return softleaf_type(entry) == SOFTLEAF_SWAP;
 }
 
+/**
+ * softleaf_is_migration_device_private() - Is this leaf entry a migration
+ * device private entry?
+ * @entry: Leaf entry.
+ *
+ * Returns: true if the leaf entry is a device private entry, otherwise false.
+ */
+static inline bool softleaf_is_migration_device_private(softleaf_t entry)
+{
+	switch (softleaf_type(entry)) {
+	case SOFTLEAF_MIGRATION_DEVICE_READ:
+	case SOFTLEAF_MIGRATION_DEVICE_WRITE:
+	case SOFTLEAF_MIGRATION_DEVICE_READ_EXCLUSIVE:
+		return true;
+	default:
+		return false;
+	}
+}
+
+/**
+ * softleaf_is_migration_device_private_write() - Is this leaf entry a writable
+ * device private migration entry?
+ * @entry: Leaf entry.
+ *
+ * Returns: true if the leaf entry is a writable device private migration entry,
+ * otherwise false.
+ */
+static inline bool softleaf_is_migration_device_private_write(softleaf_t entry)
+{
+	return softleaf_type(entry) == SOFTLEAF_MIGRATION_DEVICE_WRITE;
+}
+
+/**
+ * softleaf_is_migration_read_exclusive() - Is this leaf entry an exclusive
+ * readable device private migration entry?
+ * @entry: Leaf entry.
+ *
+ * Returns: true if the leaf entry is an exclusive readable device private
+ * migration entry, otherwise false.
+ */
+static inline bool softleaf_is_migration_device_private_read_exclusive(softleaf_t entry)
+{
+	return softleaf_type(entry) == SOFTLEAF_MIGRATION_DEVICE_READ_EXCLUSIVE;
+}
+
 /**
  * softleaf_is_migration_write() - Is this leaf entry a writable migration entry?
  * @entry: Leaf entry.
  *
- * Returns: true if the leaf entry is a writable migration entry, otherwise
- * false.
+ * Returns: true if the leaf entry is a writable migration entry or a writable
+ * device private migration entry, otherwise false.
  */
 static inline bool softleaf_is_migration_write(softleaf_t entry)
 {
-	return softleaf_type(entry) == SOFTLEAF_MIGRATION_WRITE;
+	return softleaf_type(entry) == SOFTLEAF_MIGRATION_WRITE ||
+	       softleaf_is_migration_device_private_write(entry);
 }
 
 /**
@@ -219,12 +274,13 @@ static inline bool softleaf_is_migration_read(softleaf_t entry)
  * readable migration entry?
  * @entry: Leaf entry.
  *
- * Returns: true if the leaf entry is an exclusive readable migration entry,
- * otherwise false.
+ * Returns: true if the leaf entry is an exclusive readable migration entry or
+ * exclusive readable device private migration entry, otherwise false.
  */
 static inline bool softleaf_is_migration_read_exclusive(softleaf_t entry)
 {
-	return softleaf_type(entry) == SOFTLEAF_MIGRATION_READ_EXCLUSIVE;
+	return softleaf_type(entry) == SOFTLEAF_MIGRATION_READ_EXCLUSIVE ||
+	       softleaf_is_migration_device_private_read_exclusive(entry);
 }
 
 /**
@@ -241,7 +297,7 @@ static inline bool softleaf_is_migration(softleaf_t entry)
 	case SOFTLEAF_MIGRATION_WRITE:
 		return true;
 	default:
-		return false;
+		return softleaf_is_migration_device_private(entry);
 	}
 }
 
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 38ca3df68716..c15e3b3067cd 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -74,12 +74,18 @@ static inline int current_is_kswapd(void)
  *
  * When a page is mapped by the device for exclusive access we set the CPU page
  * table entries to a special SWP_DEVICE_EXCLUSIVE entry.
+ *
+ * Because device private pages do not use regular PFNs, special migration
+ * entries are also needed.
  */
 #ifdef CONFIG_DEVICE_PRIVATE
-#define SWP_DEVICE_NUM 3
+#define SWP_DEVICE_NUM 6
 #define SWP_DEVICE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM)
 #define SWP_DEVICE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+1)
 #define SWP_DEVICE_EXCLUSIVE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+2)
+#define SWP_MIGRATION_DEVICE_READ (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+3)
+#define SWP_MIGRATION_DEVICE_READ_EXCLUSIVE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+4)
+#define SWP_MIGRATION_DEVICE_WRITE (MAX_SWAPFILES+SWP_HWPOISON_NUM+SWP_MIGRATION_NUM+5)
 #else
 #define SWP_DEVICE_NUM 0
 #endif
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 72aa636fdb48..2bd01f97b4f0 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -148,6 +148,43 @@ static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
 	return swp_entry(SWP_DEVICE_EXCLUSIVE, offset);
 }
 
+static inline swp_entry_t make_readable_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(SWP_MIGRATION_DEVICE_READ, offset);
+}
+
+static inline swp_entry_t make_writable_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(SWP_MIGRATION_DEVICE_WRITE, offset);
+}
+
+static inline bool is_device_private_migration_entry(swp_entry_t entry)
+{
+	return unlikely(swp_type(entry) == SWP_MIGRATION_DEVICE_READ ||
+			swp_type(entry) == SWP_MIGRATION_DEVICE_READ_EXCLUSIVE ||
+			swp_type(entry) == SWP_MIGRATION_DEVICE_WRITE);
+}
+
+static inline bool is_readable_device_migration_private_entry(swp_entry_t entry)
+{
+	return unlikely(swp_type(entry) == SWP_MIGRATION_DEVICE_READ);
+}
+
+static inline bool is_writable_device_migration_private_entry(swp_entry_t entry)
+{
+	return unlikely(swp_type(entry) == SWP_MIGRATION_DEVICE_WRITE);
+}
+
+static inline swp_entry_t make_readable_exclusive_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(SWP_MIGRATION_DEVICE_READ_EXCLUSIVE, offset);
+}
+
+static inline bool is_readable_exclusive_device_private_migration_entry(swp_entry_t entry)
+{
+	return swp_type(entry) == SWP_MIGRATION_DEVICE_READ_EXCLUSIVE;
+}
+
 #else /* CONFIG_DEVICE_PRIVATE */
 static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
 {
@@ -164,6 +201,36 @@ static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(0, 0);
+}
+
+static inline swp_entry_t make_writable_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(0, 0);
+}
+
+static inline bool is_device_private_migration_entry(swp_entry_t entry)
+{
+	return false;
+}
+
+static inline bool is_writable_device_migration_private_entry(swp_entry_t entry)
+{
+	return false;
+}
+
+static inline swp_entry_t make_readable_exclusive_migration_device_private_entry(pgoff_t offset)
+{
+	return swp_entry(0, 0);
+}
+
+static inline bool is_readable_exclusive_device_private_migration_entry(swp_entry_t entry)
+{
+	return false;
+}
+
 #endif /* CONFIG_DEVICE_PRIVATE */
 
 #ifdef CONFIG_MIGRATION
@@ -175,6 +242,9 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 
 static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
 {
+	if (is_device_private_page(page))
+		return make_readable_migration_device_private_entry(page_to_pfn(page));
+
 	return swp_entry(SWP_MIGRATION_READ, page_to_pfn(page));
 }
 
@@ -185,6 +255,9 @@ static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset
 
 static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
 {
+	if (is_device_private_page(page))
+		return make_readable_exclusive_migration_device_private_entry(page_to_pfn(page));
+
 	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, page_to_pfn(page));
 }
 
@@ -195,6 +268,9 @@ static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 
 static inline swp_entry_t make_writable_migration_entry_from_page(struct page *page)
 {
+	if (is_device_private_page(page))
+		return make_writable_migration_device_private_entry(page_to_pfn(page));
+
 	return swp_entry(SWP_MIGRATION_WRITE, page_to_pfn(page));
 }
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 08c68e2e3f06..bbfe5e87884a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1800,7 +1800,11 @@ static void copy_huge_non_present_pmd(
 
 	if (softleaf_is_migration_write(entry) ||
 	    softleaf_is_migration_read_exclusive(entry)) {
-		entry = make_readable_migration_entry(swp_offset(entry));
+		if (softleaf_is_migration_device_private_write(entry) ||
+		    softleaf_is_migration_device_private_read_exclusive(entry))
+			entry = make_readable_migration_device_private_entry(swp_offset(entry));
+		else
+			entry = make_readable_migration_entry(swp_offset(entry));
 		pmd = swp_entry_to_pmd(entry);
 		if (pmd_swp_soft_dirty(*src_pmd))
 			pmd = pmd_swp_mksoft_dirty(pmd);
@@ -2523,10 +2527,17 @@ static void change_non_present_huge_pmd(struct mm_struct *mm,
 		 * A protection check is difficult so
 		 * just be safe and disable write
 		 */
-		if (folio_test_anon(folio))
-			entry = make_readable_exclusive_migration_entry(swp_offset(entry));
-		else
-			entry = make_readable_migration_entry(swp_offset(entry));
+		if (folio_test_anon(folio)) {
+			if (folio_is_device_private(folio))
+				entry = make_readable_exclusive_migration_device_private_entry(swp_offset(entry));
+			else
+				entry = make_readable_exclusive_migration_entry(swp_offset(entry));
+		} else {
+			if (folio_is_device_private(folio))
+				entry = make_readable_migration_device_private_entry(swp_offset(entry));
+			else
+				entry = make_readable_migration_entry(swp_offset(entry));
+		}
 		newpmd = swp_entry_to_pmd(entry);
 		if (pmd_swp_soft_dirty(*pmd))
 			newpmd = pmd_swp_mksoft_dirty(newpmd);
diff --git a/mm/memory.c b/mm/memory.c
index 2a55edc48a65..8e5e305bc2dc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -963,8 +963,14 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 			 * to be set to read. A previously exclusive entry is
 			 * now shared.
 			 */
-			entry = make_readable_migration_entry(
-							swp_offset(entry));
+
+			if (softleaf_is_migration_device_private(entry))
+				entry = make_readable_migration_device_private_entry(
+								swp_offset(entry));
+			else
+				entry = make_readable_migration_entry(
+								swp_offset(entry));
+
 			pte = softleaf_to_pte(entry);
 			if (pte_swp_soft_dirty(orig_pte))
 				pte = pte_swp_mksoft_dirty(pte);
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 283889e4f1ce..61542a80074b 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -327,11 +327,22 @@ static long change_pte_range(struct mmu_gather *tlb,
 				 * A protection check is difficult so
 				 * just be safe and disable write
 				 */
-				if (folio_test_anon(folio))
-					entry = make_readable_exclusive_migration_entry(
-							     swp_offset(entry));
-				else
-					entry = make_readable_migration_entry(swp_offset(entry));
+				if (!is_writable_device_migration_private_entry(entry)) {
+					if (folio_test_anon(folio))
+						entry = make_readable_exclusive_migration_entry(
+								swp_offset(entry));
+					else
+						entry = make_readable_migration_entry(
+								swp_offset(entry));
+				} else {
+					if (folio_test_anon(folio))
+						entry = make_readable_exclusive_migration_device_private_entry(
+								swp_offset(entry));
+					else
+						entry = make_readable_migration_device_private_entry(
+								swp_offset(entry));
+				}
+
 				newpte = swp_entry_to_pte(entry);
 				if (pte_swp_soft_dirty(oldpte))
 					newpte = pte_swp_mksoft_dirty(newpte);
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index 7fddafed3ebb..b19820a51e95 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -255,7 +255,8 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 
 				if (!softleaf_is_migration(entry) ||
 				    !check_pmd(softleaf_to_pfn(entry),
-					       softleaf_is_device_private(entry),
+					       softleaf_is_device_private(entry) ||
+					       softleaf_is_migration_device_private(entry),
 					       pvmw))
 					return not_found(pvmw);
 				return true;
-- 
2.34.1

[PATCH v1 5/8] mm: Add helpers to create device private entries from struct pages

[Jordan Niethe]

To create a new device private entry for a given struct page, that page
is first converted to its pfn, before passing the pfn to
make_writable_device_private_entry() (and friends).

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have a
pfn and must be handled separately.

Prepare for this with a new set of helpers:

- make_readable_device_private_entry_from_page()
- make_writable_device_private_entry_from_page()

These helpers take a struct page as parameter instead of a pfn. This
will allow more flexibility for handling the swap offset field
differently for device private pages.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
---
v1:
  - New to series
---
 include/linux/swapops.h | 20 ++++++++++++++++++++
 mm/huge_memory.c        | 14 ++++++--------
 mm/memory.c             |  4 ++--
 mm/migrate.c            |  6 ++----
 mm/migrate_device.c     | 12 ++++--------
 5 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 2bd01f97b4f0..ddf2763d69e9 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -138,11 +138,21 @@ static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
 	return swp_entry(SWP_DEVICE_READ, offset);
 }
 
+static inline swp_entry_t make_readable_device_private_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_DEVICE_READ, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_writable_device_private_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_DEVICE_WRITE, offset);
 }
 
+static inline swp_entry_t make_writable_device_private_entry_from_page(struct page *page)
+{
+	return swp_entry(SWP_DEVICE_WRITE, page_to_pfn(page));
+}
+
 static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
 {
 	return swp_entry(SWP_DEVICE_EXCLUSIVE, offset);
@@ -191,11 +201,21 @@ static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_readable_device_private_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_writable_device_private_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
 }
 
+static inline swp_entry_t make_writable_device_private_entry_from_page(struct page *page)
+{
+	return swp_entry(0, 0);
+}
+
 static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
 {
 	return swp_entry(0, 0);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index bbfe5e87884a..31ea473cbcbd 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3225,11 +3225,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 			 * is false.
 			 */
 			if (write)
-				swp_entry = make_writable_device_private_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_writable_device_private_entry_from_page(
+							page + i);
 			else
-				swp_entry = make_readable_device_private_entry(
-							page_to_pfn(page + i));
+				swp_entry = make_readable_device_private_entry_from_page(
+							page + i);
 			/*
 			 * Young and dirty bits are not progated via swp_entry
 			 */
@@ -4956,11 +4956,9 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 		swp_entry_t entry;
 
 		if (pmd_write(pmde))
-			entry = make_writable_device_private_entry(
-							page_to_pfn(new));
+			entry = make_writable_device_private_entry_from_page(new);
 		else
-			entry = make_readable_device_private_entry(
-							page_to_pfn(new));
+			entry = make_readable_device_private_entry_from_page(new);
 		pmde = swp_entry_to_pmd(entry);
 
 		if (pmd_swp_soft_dirty(*pvmw->pmd))
diff --git a/mm/memory.c b/mm/memory.c
index 8e5e305bc2dc..076d7acb7267 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1005,8 +1005,8 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		 */
 		if (softleaf_is_device_private_write(entry) &&
 		    is_cow_mapping(vm_flags)) {
-			entry = make_readable_device_private_entry(
-							swp_offset(entry));
+			entry = make_readable_device_private_entry
+							(swp_offset(entry));
 			pte = swp_entry_to_pte(entry);
 			if (pte_swp_uffd_wp(orig_pte))
 				pte = pte_swp_mkuffd_wp(pte);
diff --git a/mm/migrate.c b/mm/migrate.c
index 5169f9717f60..9ec9bcd37882 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -399,11 +399,9 @@ static bool remove_migration_pte(struct folio *folio,
 
 		if (unlikely(is_device_private_page(new))) {
 			if (pte_write(pte))
-				entry = make_writable_device_private_entry(
-							page_to_pfn(new));
+				entry = make_writable_device_private_entry_from_page(new);
 			else
-				entry = make_readable_device_private_entry(
-							page_to_pfn(new));
+				entry = make_readable_device_private_entry_from_page(new);
 			pte = softleaf_to_pte(entry);
 			if (pte_swp_soft_dirty(old_pte))
 				pte = pte_swp_mksoft_dirty(pte);
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 7eef21d63364..5cc58a5876a0 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -842,11 +842,9 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
 		swp_entry_t swp_entry;
 
 		if (vma->vm_flags & VM_WRITE)
-			swp_entry = make_writable_device_private_entry(
-						page_to_pfn(page));
+			swp_entry = make_writable_device_private_entry_from_page(page);
 		else
-			swp_entry = make_readable_device_private_entry(
-						page_to_pfn(page));
+			swp_entry = make_readable_device_private_entry_from_page(page);
 		entry = swp_entry_to_pmd(swp_entry);
 	} else {
 		if (folio_is_zone_device(folio) &&
@@ -1039,11 +1037,9 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 		swp_entry_t swp_entry;
 
 		if (vma->vm_flags & VM_WRITE)
-			swp_entry = make_writable_device_private_entry(
-						page_to_pfn(page));
+			swp_entry = make_writable_device_private_entry_from_page(page);
 		else
-			swp_entry = make_readable_device_private_entry(
-						page_to_pfn(page));
+			swp_entry = make_readable_device_private_entry_from_page(page);
 		entry = swp_entry_to_pte(swp_entry);
 	} else {
 		if (folio_is_zone_device(folio) &&
-- 
2.34.1

[PATCH v1 6/8] mm/util: Add flag to track device private pages in page snapshots

[Jordan Niethe]

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have
normal pfns and must be handled separately.

Add a new flag PAGE_SNAPSHOT_DEVICE_PRIVATE to track when the pfn of a
page snapshot is a device private page.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
v1:
  - No change
---
 fs/proc/page.c     | 6 ++++--
 include/linux/mm.h | 7 ++++---
 mm/util.c          | 3 +++
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/proc/page.c b/fs/proc/page.c
index f9b2c2c906cd..adca0e681442 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -191,10 +191,12 @@ u64 stable_page_flags(const struct page *page)
 	         folio_test_large_rmappable(folio)) {
 		/* Note: we indicate any THPs here, not just PMD-sized ones */
 		u |= 1 << KPF_THP;
-	} else if (is_huge_zero_pfn(ps.pfn)) {
+	} else if (!(ps.flags & PAGE_SNAPSHOT_DEVICE_PRIVATE) &&
+		   is_huge_zero_pfn(ps.pfn)) {
 		u |= 1 << KPF_ZERO_PAGE;
 		u |= 1 << KPF_THP;
-	} else if (is_zero_pfn(ps.pfn)) {
+	} else if (!(ps.flags & PAGE_SNAPSHOT_DEVICE_PRIVATE)
+		   && is_zero_pfn(ps.pfn)) {
 		u |= 1 << KPF_ZERO_PAGE;
 	}
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 15076261d0c2..e65329e1969f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4623,9 +4623,10 @@ static inline bool page_pool_page_is_pp(const struct page *page)
 }
 #endif
 
-#define PAGE_SNAPSHOT_FAITHFUL (1 << 0)
-#define PAGE_SNAPSHOT_PG_BUDDY (1 << 1)
-#define PAGE_SNAPSHOT_PG_IDLE  (1 << 2)
+#define PAGE_SNAPSHOT_FAITHFUL		(1 << 0)
+#define PAGE_SNAPSHOT_PG_BUDDY		(1 << 1)
+#define PAGE_SNAPSHOT_PG_IDLE		(1 << 2)
+#define PAGE_SNAPSHOT_DEVICE_PRIVATE	(1 << 3)
 
 struct page_snapshot {
 	struct folio folio_snapshot;
diff --git a/mm/util.c b/mm/util.c
index 97cae40c0209..65e3f1a97d76 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1218,6 +1218,9 @@ static void set_ps_flags(struct page_snapshot *ps, const struct folio *folio,
 
 	if (folio_test_idle(folio))
 		ps->flags |= PAGE_SNAPSHOT_PG_IDLE;
+
+	if (is_device_private_page(page))
+		ps->flags |= PAGE_SNAPSHOT_DEVICE_PRIVATE;
 }
 
 /**
-- 
2.34.1

[PATCH v1 7/8] mm/hmm: Add flag to track device private pages

[Jordan Niethe]

A future change will remove device private pages from the physical
address space. This will mean that device private pages no longer have
normal pfns and must be handled separately.

Prepare for this by adding a HMM_PFN_DEVICE_PRIVATE flag to indicate
that a hmm_pfn contains a PFN for a device private page.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>

---
v1:
  - Update HMM_PFN_ORDER_SHIFT
  - Handle hmm_vma_handle_absent_pmd()
---
 include/linux/hmm.h | 4 +++-
 mm/hmm.c            | 5 +++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index db75ffc949a7..d8756c341620 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -23,6 +23,7 @@ struct mmu_interval_notifier;
  * HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
  * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
  *                 fail. ie poisoned memory, special pages, no vma, etc
+ * HMM_PFN_DEVICE_PRIVATE - the pfn field contains a DEVICE_PRIVATE pfn.
  * HMM_PFN_P2PDMA - P2P page
  * HMM_PFN_P2PDMA_BUS - Bus mapped P2P transfer
  * HMM_PFN_DMA_MAPPED - Flag preserved on input-to-output transformation
@@ -40,6 +41,7 @@ enum hmm_pfn_flags {
 	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
 	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
 	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
+	HMM_PFN_DEVICE_PRIVATE = 1UL << (BITS_PER_LONG - 7),
 	/*
 	 * Sticky flags, carried from input to output,
 	 * don't forget to update HMM_PFN_INOUT_FLAGS
@@ -48,7 +50,7 @@ enum hmm_pfn_flags {
 	HMM_PFN_P2PDMA     = 1UL << (BITS_PER_LONG - 5),
 	HMM_PFN_P2PDMA_BUS = 1UL << (BITS_PER_LONG - 6),
 
-	HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 11),
+	HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 12),
 
 	/* Input flags */
 	HMM_PFN_REQ_FAULT = HMM_PFN_VALID,
diff --git a/mm/hmm.c b/mm/hmm.c
index 4ec74c18bef6..14895fa6575f 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -267,7 +267,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 		if (softleaf_is_device_private(entry) &&
 		    page_pgmap(softleaf_to_page(entry))->owner ==
 		    range->dev_private_owner) {
-			cpu_flags = HMM_PFN_VALID;
+			cpu_flags = HMM_PFN_VALID | HMM_PFN_DEVICE_PRIVATE;
 			if (softleaf_is_device_private_write(entry))
 				cpu_flags |= HMM_PFN_WRITE;
 			new_pfn_flags = softleaf_to_pfn(entry) | cpu_flags;
@@ -347,7 +347,8 @@ static int hmm_vma_handle_absent_pmd(struct mm_walk *walk, unsigned long start,
 	    softleaf_to_folio(entry)->pgmap->owner ==
 	    range->dev_private_owner) {
 		unsigned long cpu_flags = HMM_PFN_VALID |
-			hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT);
+			hmm_pfn_flags_order(PMD_SHIFT - PAGE_SHIFT) |
+			HMM_PFN_DEVICE_PRIVATE;
 		unsigned long pfn = softleaf_to_pfn(entry);
 		unsigned long i;
 
-- 
2.34.1

[PATCH v1 8/8] mm: Remove device private pages from the physical address space

[Jordan Niethe]

Currently when creating these device private struct pages, the first
step is to use request_free_mem_region() to get a range of physical
address space large enough to represent the devices memory. This
allocated physical address range is then remapped as device private
memory using memremap_pages().

Needing allocation of physical address space has some problems:

  1) There may be insufficient physical address space to represent the
     device memory. KASLR reducing the physical address space and VM
     configurations with limited physical address space increase the
     likelihood of hitting this especially as device memory increases. This
     has been observed to prevent device private from being initialized.

  2) Attempting to add the device private pages to the linear map at
     addresses beyond the actual physical memory causes issues on
     architectures like aarch64 meaning the feature does not work there.

Instead of using the physical address space, introduce a device private
address space and allocate devices regions from there to represent the
device private pages.

Introduce a new interface memremap_device_private_pagemap() that
allocates a requested amount of device private address space and creates
the necessary device private pages.

To support this new interface, struct dev_pagemap needs some changes:

  - Add a new dev_pagemap::nr_pages field as an input parameter.
  - Add a new dev_pagemap::pages array to store the device
    private pages.

When using memremap_device_private_pagemap(), rather then passing in
dev_pagemap::ranges[dev_pagemap::nr_ranges] of physical address space to
be remapped, dev_pagemap::nr_ranges will always be 1, and the device
private range that is reserved is returned in dev_pagemap::range.

Forbid calling memremap_pages() with dev_pagemap::ranges::type =
MEMORY_DEVICE_PRIVATE.

Represent this device private address space using a new
device_private_pgmap_tree maple tree. This tree maps a given device
private address to a struct dev_pagemap, where a specific device private
page may then be looked up in that dev_pagemap::pages array.

Device private address space can be reclaimed and the assoicated device
private pages freed using the corresponding new
memunmap_device_private_pagemap() interface.

Because the device private pages now live outside the physical address
space, they no longer have a normal PFN. This means that page_to_pfn(),
et al. are no longer meaningful.

Introduce helpers:

  - device_private_page_to_offset()
  - device_private_folio_to_offset()

to take a given device private page / folio and return its offset within
the device private address space.

Update the places where we previously converted a device private page to
a PFN to use these new helpers. When we encounter a device private
offset, instead of looking up its page within the pagemap use
device_private_offset_to_page() instead.

Update the existing users:

 - lib/test_hmm.c
 - ppc ultravisor
 - drm/amd/amdkfd
 - gpu/drm/xe
 - gpu/drm/nouveau

to use the new memremap_device_private_pagemap() interface.

Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Alistair Popple <apopple@nvidia.com>

---

NOTE: The updates to the existing drivers have only been compile tested.
I'll need some help in testing these drivers.

v1:
- Include NUMA node paramater for memremap_device_private_pagemap()
- Add devm_memremap_device_private_pagemap() and friends
- Update existing users of memremap_pages():
    - ppc ultravisor
    - drm/amd/amdkfd
    - gpu/drm/xe
    - gpu/drm/nouveau
- Update for HMM huge page support
- Guard device_private_offset_to_page and friends with CONFIG_ZONE_DEVICE
---
 Documentation/mm/hmm.rst                 |  11 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c       |  43 ++---
 drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  29 ++--
 drivers/gpu/drm/drm_pagemap.c            |   2 +-
 drivers/gpu/drm/nouveau/nouveau_dmem.c   |  37 ++---
 drivers/gpu/drm/xe/xe_svm.c              |  28 +---
 include/linux/hmm.h                      |   3 +
 include/linux/leafops.h                  |  16 +-
 include/linux/memremap.h                 |  64 +++++++-
 include/linux/migrate.h                  |   4 +
 include/linux/mm.h                       |   2 +
 include/linux/rmap.h                     |   5 +-
 include/linux/swapops.h                  |  13 +-
 lib/test_hmm.c                           |  73 +++++----
 mm/debug.c                               |   9 +-
 mm/memremap.c                            | 193 ++++++++++++++++++-----
 mm/migrate_device.c                      |  12 +-
 mm/mm_init.c                             |   8 +-
 mm/page_vma_mapped.c                     |  13 ++
 mm/rmap.c                                |  43 +++--
 mm/util.c                                |   5 +-
 21 files changed, 406 insertions(+), 207 deletions(-)

diff --git a/Documentation/mm/hmm.rst b/Documentation/mm/hmm.rst
index 7d61b7a8b65b..27067a6a2408 100644
--- a/Documentation/mm/hmm.rst
+++ b/Documentation/mm/hmm.rst
@@ -276,17 +276,12 @@ These can be allocated and freed with::
     struct resource *res;
     struct dev_pagemap pagemap;
 
-    res = request_free_mem_region(&iomem_resource, /* number of bytes */,
-                                  "name of driver resource");
     pagemap.type = MEMORY_DEVICE_PRIVATE;
-    pagemap.range.start = res->start;
-    pagemap.range.end = res->end;
-    pagemap.nr_range = 1;
+    pagemap.nr_pages = /* number of pages */;
     pagemap.ops = &device_devmem_ops;
-    memremap_pages(&pagemap, numa_node_id());
+    memremap_device_private_pagemap(&pagemap, numa_node_id());
 
-    memunmap_pages(&pagemap);
-    release_mem_region(pagemap.range.start, range_len(&pagemap.range));
+    memunmap_device_private_pagemap(&pagemap);
 
 There are also devm_request_free_mem_region(), devm_memremap_pages(),
 devm_memunmap_pages(), and devm_release_mem_region() when the resources can
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index dac5d6454920..d4201536155c 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -636,7 +636,7 @@ void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *slot,
 		mutex_lock(&kvm->arch.uvmem_lock);
 
 		if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
-			uvmem_page = pfn_to_page(uvmem_pfn);
+			uvmem_page = device_private_offset_to_page(uvmem_pfn);
 			pvt = uvmem_page->zone_device_data;
 			pvt->skip_page_out = skip_page_out;
 			pvt->remove_gfn = true;
@@ -721,7 +721,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
 	pvt->gpa = gpa;
 	pvt->kvm = kvm;
 
-	dpage = pfn_to_page(uvmem_pfn);
+	dpage = device_private_offset_to_page(uvmem_pfn);
 	dpage->zone_device_data = pvt;
 	zone_device_page_init(dpage, 0);
 	return dpage;
@@ -784,7 +784,7 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma,
 		}
 	}
 
-	*mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
+	*mig.dst = migrate_pfn(device_private_page_to_offset(dpage)) | MIGRATE_PFN_DEVICE;
 	migrate_vma_pages(&mig);
 out_finalize:
 	migrate_vma_finalize(&mig);
@@ -888,7 +888,7 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 	srcu_idx = srcu_read_lock(&kvm->srcu);
 	mutex_lock(&kvm->arch.uvmem_lock);
 	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
-		uvmem_page = pfn_to_page(uvmem_pfn);
+		uvmem_page = device_private_offset_to_page(uvmem_pfn);
 		pvt = uvmem_page->zone_device_data;
 		pvt->skip_page_out = true;
 		/*
@@ -906,7 +906,7 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 
 	mutex_lock(&kvm->arch.uvmem_lock);
 	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, &uvmem_pfn)) {
-		uvmem_page = pfn_to_page(uvmem_pfn);
+		uvmem_page = device_private_offset_to_page(uvmem_pfn);
 		pvt = uvmem_page->zone_device_data;
 		pvt->skip_page_out = true;
 		pvt->remove_gfn = false; /* it continues to be a valid GFN */
@@ -1017,7 +1017,7 @@ static vm_fault_t kvmppc_uvmem_migrate_to_ram(struct vm_fault *vmf)
 static void kvmppc_uvmem_folio_free(struct folio *folio)
 {
 	struct page *page = &folio->page;
-	unsigned long pfn = page_to_pfn(page) -
+	unsigned long pfn = device_private_page_to_offset(page) -
 			(kvmppc_uvmem_pgmap.range.start >> PAGE_SHIFT);
 	struct kvmppc_uvmem_page_pvt *pvt;
 
@@ -1159,8 +1159,6 @@ int kvmppc_uvmem_init(void)
 {
 	int ret = 0;
 	unsigned long size;
-	struct resource *res;
-	void *addr;
 	unsigned long pfn_last, pfn_first;
 
 	size = kvmppc_get_secmem_size();
@@ -1174,27 +1172,18 @@ int kvmppc_uvmem_init(void)
 		goto out;
 	}
 
-	res = request_free_mem_region(&iomem_resource, size, "kvmppc_uvmem");
-	if (IS_ERR(res)) {
-		ret = PTR_ERR(res);
-		goto out;
-	}
-
 	kvmppc_uvmem_pgmap.type = MEMORY_DEVICE_PRIVATE;
-	kvmppc_uvmem_pgmap.range.start = res->start;
-	kvmppc_uvmem_pgmap.range.end = res->end;
 	kvmppc_uvmem_pgmap.nr_range = 1;
+	kvmppc_uvmem_pgmap.nr_pages = size / PAGE_SIZE;
 	kvmppc_uvmem_pgmap.ops = &kvmppc_uvmem_ops;
 	/* just one global instance: */
 	kvmppc_uvmem_pgmap.owner = &kvmppc_uvmem_pgmap;
-	addr = memremap_pages(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
-	if (IS_ERR(addr)) {
-		ret = PTR_ERR(addr);
-		goto out_free_region;
-	}
+	ret = memremap_device_private_pagemap(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
+	if (ret)
+		goto out;
 
-	pfn_first = res->start >> PAGE_SHIFT;
-	pfn_last = pfn_first + (resource_size(res) >> PAGE_SHIFT);
+	pfn_first = kvmppc_uvmem_pgmap.range.start >> PAGE_SHIFT;
+	pfn_last = pfn_first + (range_len(&kvmppc_uvmem_pgmap.range) >> PAGE_SHIFT);
 	kvmppc_uvmem_bitmap = bitmap_zalloc(pfn_last - pfn_first, GFP_KERNEL);
 	if (!kvmppc_uvmem_bitmap) {
 		ret = -ENOMEM;
@@ -1204,9 +1193,7 @@ int kvmppc_uvmem_init(void)
 	pr_info("KVMPPC-UVMEM: Secure Memory size 0x%lx\n", size);
 	return ret;
 out_unmap:
-	memunmap_pages(&kvmppc_uvmem_pgmap);
-out_free_region:
-	release_mem_region(res->start, size);
+	memunmap_device_private_pagemap(&kvmppc_uvmem_pgmap);
 out:
 	return ret;
 }
@@ -1216,8 +1203,6 @@ void kvmppc_uvmem_free(void)
 	if (!kvmppc_uvmem_bitmap)
 		return;
 
-	memunmap_pages(&kvmppc_uvmem_pgmap);
-	release_mem_region(kvmppc_uvmem_pgmap.range.start,
-			   range_len(&kvmppc_uvmem_pgmap.range));
+	memunmap_device_private_pagemap(&kvmppc_uvmem_pgmap);
 	bitmap_free(kvmppc_uvmem_bitmap);
 }
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
index 0257c6e7f680..be6a07e9a75c 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
@@ -214,7 +214,7 @@ svm_migrate_get_vram_page(struct svm_range *prange, unsigned long pfn)
 {
 	struct page *page;
 
-	page = pfn_to_page(pfn);
+	page = device_private_offset_to_page(pfn);
 	svm_range_bo_ref(prange->svm_bo);
 	page->zone_device_data = prange->svm_bo;
 	zone_device_page_init(page, 0);
@@ -225,7 +225,7 @@ svm_migrate_put_vram_page(struct amdgpu_device *adev, unsigned long addr)
 {
 	struct page *page;
 
-	page = pfn_to_page(svm_migrate_addr_to_pfn(adev, addr));
+	page = device_private_offset_to_page(svm_migrate_addr_to_pfn(adev, addr));
 	unlock_page(page);
 	put_page(page);
 }
@@ -235,7 +235,7 @@ svm_migrate_addr(struct amdgpu_device *adev, struct page *page)
 {
 	unsigned long addr;
 
-	addr = page_to_pfn(page) << PAGE_SHIFT;
+	addr = device_private_page_to_offset(page) << PAGE_SHIFT;
 	return (addr - adev->kfd.pgmap.range.start);
 }
 
@@ -1021,9 +1021,9 @@ int kgd2kfd_init_zone_device(struct amdgpu_device *adev)
 {
 	struct amdgpu_kfd_dev *kfddev = &adev->kfd;
 	struct dev_pagemap *pgmap;
-	struct resource *res = NULL;
 	unsigned long size;
 	void *r;
+	int ret;
 
 	/* Page migration works on gfx9 or newer */
 	if (amdgpu_ip_version(adev, GC_HWIP, 0) < IP_VERSION(9, 0, 1))
@@ -1044,11 +1044,7 @@ int kgd2kfd_init_zone_device(struct amdgpu_device *adev)
 		pgmap->range.end = adev->gmc.aper_base + adev->gmc.aper_size - 1;
 		pgmap->type = MEMORY_DEVICE_COHERENT;
 	} else {
-		res = devm_request_free_mem_region(adev->dev, &iomem_resource, size);
-		if (IS_ERR(res))
-			return PTR_ERR(res);
-		pgmap->range.start = res->start;
-		pgmap->range.end = res->end;
+		pgmap->nr_pages = size / PAGE_SIZE;
 		pgmap->type = MEMORY_DEVICE_PRIVATE;
 	}
 
@@ -1059,14 +1055,19 @@ int kgd2kfd_init_zone_device(struct amdgpu_device *adev)
 	/* Device manager releases device-specific resources, memory region and
 	 * pgmap when driver disconnects from device.
 	 */
-	r = devm_memremap_pages(adev->dev, pgmap);
-	if (IS_ERR(r)) {
+	if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
+		ret = devm_memremap_device_private_pagemap(adev->dev, pgmap);
+	} else {
+		r = devm_memremap_pages(adev->dev, pgmap);
+		if (IS_ERR(r))
+			ret = PTR_ERR(r);
+	}
+
+	if (ret) {
 		pr_err("failed to register HMM device memory\n");
-		if (pgmap->type == MEMORY_DEVICE_PRIVATE)
-			devm_release_mem_region(adev->dev, res->start, resource_size(res));
 		/* Disable SVM support capability */
 		pgmap->type = 0;
-		return PTR_ERR(r);
+		return ret;
 	}
 
 	pr_debug("reserve %ldMB system memory for VRAM pages struct\n",
diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
index 0c756d73419f..c703fc318f13 100644
--- a/drivers/gpu/drm/drm_pagemap.c
+++ b/drivers/gpu/drm/drm_pagemap.c
@@ -401,7 +401,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
 		goto err_finalize;
 
 	for (i = 0; i < npages; ++i) {
-		struct page *page = pfn_to_page(migrate.dst[i]);
+		struct page *page = device_private_offset_to_page(migrate.dst[i]);
 
 		pages[i] = page;
 		migrate.dst[i] = migrate_pfn(migrate.dst[i]) | MIGRATE_PFN_DEVICE;
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 2bd80c6f5bcd..297e1d8b775a 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -109,7 +109,7 @@ static struct nouveau_drm *page_to_drm(struct page *page)
 unsigned long nouveau_dmem_page_addr(struct page *page)
 {
 	struct nouveau_dmem_chunk *chunk = nouveau_page_to_chunk(page);
-	unsigned long off = (page_to_pfn(page) << PAGE_SHIFT) -
+	unsigned long off = (device_private_page_to_offset(page) << PAGE_SHIFT) -
 				chunk->pagemap.range.start;
 
 	return chunk->bo->offset + off;
@@ -297,9 +297,7 @@ nouveau_dmem_chunk_alloc(struct nouveau_drm *drm, struct page **ppage,
 			 bool is_large)
 {
 	struct nouveau_dmem_chunk *chunk;
-	struct resource *res;
 	struct page *page;
-	void *ptr;
 	unsigned long i, pfn_first, pfn;
 	int ret;
 
@@ -309,39 +307,28 @@ nouveau_dmem_chunk_alloc(struct nouveau_drm *drm, struct page **ppage,
 		goto out;
 	}
 
-	/* Allocate unused physical address space for device private pages. */
-	res = request_free_mem_region(&iomem_resource, DMEM_CHUNK_SIZE * NR_CHUNKS,
-				      "nouveau_dmem");
-	if (IS_ERR(res)) {
-		ret = PTR_ERR(res);
-		goto out_free;
-	}
-
 	chunk->drm = drm;
 	chunk->pagemap.type = MEMORY_DEVICE_PRIVATE;
-	chunk->pagemap.range.start = res->start;
-	chunk->pagemap.range.end = res->end;
 	chunk->pagemap.nr_range = 1;
+	chunk->pagemap.nr_pages = DMEM_CHUNK_SIZE * NR_CHUNKS / PAGE_SIZE;
 	chunk->pagemap.ops = &nouveau_dmem_pagemap_ops;
 	chunk->pagemap.owner = drm->dev;
 
 	ret = nouveau_bo_new_pin(&drm->client, NOUVEAU_GEM_DOMAIN_VRAM, DMEM_CHUNK_SIZE,
 				 &chunk->bo);
 	if (ret)
-		goto out_release;
+		goto out_free;
 
-	ptr = memremap_pages(&chunk->pagemap, numa_node_id());
-	if (IS_ERR(ptr)) {
-		ret = PTR_ERR(ptr);
+	ret = memremap_device_private_pagemap(&chunk->pagemap, numa_node_id());
+	if (ret)
 		goto out_bo_free;
-	}
 
 	mutex_lock(&drm->dmem->mutex);
 	list_add(&chunk->list, &drm->dmem->chunks);
 	mutex_unlock(&drm->dmem->mutex);
 
 	pfn_first = chunk->pagemap.range.start >> PAGE_SHIFT;
-	page = pfn_to_page(pfn_first);
+	page = device_private_offset_to_page(pfn_first);
 	spin_lock(&drm->dmem->lock);
 
 	pfn = pfn_first;
@@ -350,12 +337,12 @@ nouveau_dmem_chunk_alloc(struct nouveau_drm *drm, struct page **ppage,
 
 		if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) || !is_large) {
 			for (j = 0; j < DMEM_CHUNK_NPAGES - 1; j++, pfn++) {
-				page = pfn_to_page(pfn);
+				page = device_private_offset_to_page(pfn);
 				page->zone_device_data = drm->dmem->free_pages;
 				drm->dmem->free_pages = page;
 			}
 		} else {
-			page = pfn_to_page(pfn);
+			page = device_private_offset_to_page(pfn);
 			page->zone_device_data = drm->dmem->free_folios;
 			drm->dmem->free_folios = page_folio(page);
 			pfn += DMEM_CHUNK_NPAGES;
@@ -382,8 +369,6 @@ nouveau_dmem_chunk_alloc(struct nouveau_drm *drm, struct page **ppage,
 
 out_bo_free:
 	nouveau_bo_unpin_del(&chunk->bo);
-out_release:
-	release_mem_region(chunk->pagemap.range.start, range_len(&chunk->pagemap.range));
 out_free:
 	kfree(chunk);
 out:
@@ -541,9 +526,7 @@ nouveau_dmem_fini(struct nouveau_drm *drm)
 		nouveau_bo_unpin_del(&chunk->bo);
 		WARN_ON(chunk->callocated);
 		list_del(&chunk->list);
-		memunmap_pages(&chunk->pagemap);
-		release_mem_region(chunk->pagemap.range.start,
-				   range_len(&chunk->pagemap.range));
+		memunmap_device_private_pagemap(&chunk->pagemap);
 		kfree(chunk);
 	}
 
@@ -766,7 +749,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
 		((paddr >> PAGE_SHIFT) << NVIF_VMM_PFNMAP_V0_ADDR_SHIFT);
 	if (src & MIGRATE_PFN_WRITE)
 		*pfn |= NVIF_VMM_PFNMAP_V0_W;
-	mpfn = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
+	mpfn = migrate_pfn(device_private_page_to_offset(dpage)) | MIGRATE_PFN_DEVICE;
 	if (folio_order(page_folio(dpage)))
 		mpfn |= MIGRATE_PFN_COMPOUND;
 	return mpfn;
diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
index 55c5a0eb82e1..e89317d7e062 100644
--- a/drivers/gpu/drm/xe/xe_svm.c
+++ b/drivers/gpu/drm/xe/xe_svm.c
@@ -403,7 +403,7 @@ static u64 xe_vram_region_page_to_dpa(struct xe_vram_region *vr,
 				      struct page *page)
 {
 	u64 dpa;
-	u64 pfn = page_to_pfn(page);
+	u64 pfn = device_private_page_to_offset(page);
 	u64 offset;
 
 	xe_assert(vr->xe, is_device_private_page(page));
@@ -1470,39 +1470,27 @@ int xe_devm_add(struct xe_tile *tile, struct xe_vram_region *vr)
 {
 	struct xe_device *xe = tile_to_xe(tile);
 	struct device *dev = &to_pci_dev(xe->drm.dev)->dev;
-	struct resource *res;
-	void *addr;
 	int ret;
 
-	res = devm_request_free_mem_region(dev, &iomem_resource,
-					   vr->usable_size);
-	if (IS_ERR(res)) {
-		ret = PTR_ERR(res);
-		return ret;
-	}
-
 	vr->pagemap.type = MEMORY_DEVICE_PRIVATE;
-	vr->pagemap.range.start = res->start;
-	vr->pagemap.range.end = res->end;
 	vr->pagemap.nr_range = 1;
+	vr->pagemap.nr_pages = vr->usable_size / PAGE_SIZE;
 	vr->pagemap.ops = drm_pagemap_pagemap_ops_get();
 	vr->pagemap.owner = xe_svm_devm_owner(xe);
-	addr = devm_memremap_pages(dev, &vr->pagemap);
+	ret = devm_memremap_device_private_pagemap(dev, &vr->pagemap);
 
 	vr->dpagemap.dev = dev;
 	vr->dpagemap.ops = &xe_drm_pagemap_ops;
 
-	if (IS_ERR(addr)) {
-		devm_release_mem_region(dev, res->start, resource_size(res));
-		ret = PTR_ERR(addr);
-		drm_err(&xe->drm, "Failed to remap tile %d memory, errno %pe\n",
-			tile->id, ERR_PTR(ret));
+	if (ret) {
+		drm_err(&xe->drm, "Failed to remap tile %d memory, errno %d\n",
+			tile->id, ret);
 		return ret;
 	}
-	vr->hpa_base = res->start;
+	vr->hpa_base = vr->pagemap.range.start;
 
 	drm_dbg(&xe->drm, "Added tile %d memory [%llx-%llx] to devm, remapped to %pr\n",
-		tile->id, vr->io_start, vr->io_start + vr->usable_size, res);
+		tile->id, vr->io_start, vr->io_start + vr->usable_size, &vr->pagemap.range);
 	return 0;
 }
 #else
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index d8756c341620..25bb4df298f7 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -68,6 +68,9 @@ enum hmm_pfn_flags {
  */
 static inline struct page *hmm_pfn_to_page(unsigned long hmm_pfn)
 {
+	if (hmm_pfn & HMM_PFN_DEVICE_PRIVATE)
+		return device_private_offset_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
+
 	return pfn_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
 }
 
diff --git a/include/linux/leafops.h b/include/linux/leafops.h
index a4a5c3ad647b..34579ec047b3 100644
--- a/include/linux/leafops.h
+++ b/include/linux/leafops.h
@@ -427,7 +427,13 @@ static inline unsigned long softleaf_to_pfn(softleaf_t entry)
  */
 static inline struct page *softleaf_to_page(softleaf_t entry)
 {
-	struct page *page = pfn_to_page(softleaf_to_pfn(entry));
+	struct page *page;
+
+	if (softleaf_is_migration_device_private(entry) ||
+	    softleaf_is_device_private(entry))
+		page = device_private_entry_to_page(entry);
+	else
+		page = pfn_to_page(softleaf_to_pfn(entry));
 
 	VM_WARN_ON_ONCE(!softleaf_has_pfn(entry));
 	/*
@@ -447,7 +453,13 @@ static inline struct page *softleaf_to_page(softleaf_t entry)
  */
 static inline struct folio *softleaf_to_folio(softleaf_t entry)
 {
-	struct folio *folio = pfn_folio(softleaf_to_pfn(entry));
+	struct folio *folio;
+
+	if (softleaf_is_migration_device_private(entry) ||
+	    softleaf_is_device_private(entry))
+		folio = page_folio(device_private_entry_to_page(entry));
+	else
+		folio = pfn_folio(softleaf_to_pfn(entry));
 
 	VM_WARN_ON_ONCE(!softleaf_has_pfn(entry));
 	/*
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 713ec0435b48..c0c88735baa1 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -37,6 +37,7 @@ struct vmem_altmap {
  * backing the device memory. Doing so simplifies the implementation, but it is
  * important to remember that there are certain points at which the struct page
  * must be treated as an opaque object, rather than a "normal" struct page.
+ * Unlike "normal" struct pages, the page_to_pfn() is invalid.
  *
  * A more complete discussion of unaddressable memory may be found in
  * include/linux/hmm.h and Documentation/mm/hmm.rst.
@@ -126,9 +127,13 @@ struct dev_pagemap_ops {
  * @owner: an opaque pointer identifying the entity that manages this
  *	instance.  Used by various helpers to make sure that no
  *	foreign ZONE_DEVICE memory is accessed.
- * @nr_range: number of ranges to be mapped
- * @range: range to be mapped when nr_range == 1
+ * @nr_range: number of ranges to be mapped. Always == 1 for
+ *	MEMORY_DEVICE_PRIVATE.
+ * @range: range to be mapped when nr_range == 1. Used as an output param for
+ *	MEMORY_DEVICE_PRIVATE.
  * @ranges: array of ranges to be mapped when nr_range > 1
+ * @nr_pages: number of pages requested to be mapped for MEMORY_DEVICE_PRIVATE.
+ * @pages: array of nr_pages initialized for MEMORY_DEVICE_PRIVATE.
  */
 struct dev_pagemap {
 	struct vmem_altmap altmap;
@@ -144,6 +149,8 @@ struct dev_pagemap {
 		struct range range;
 		DECLARE_FLEX_ARRAY(struct range, ranges);
 	};
+	unsigned long nr_pages;
+	struct page *pages;
 };
 
 static inline bool pgmap_has_memory_failure(struct dev_pagemap *pgmap)
@@ -224,7 +231,14 @@ static inline bool is_fsdax_page(const struct page *page)
 }
 
 #ifdef CONFIG_ZONE_DEVICE
+void __init_zone_device_page(struct page *page, unsigned long pfn,
+	unsigned long zone_idx, int nid,
+	struct dev_pagemap *pgmap);
 void zone_device_page_init(struct page *page, unsigned int order);
+unsigned long memremap_device_private_pagemap(struct dev_pagemap *pgmap, int nid);
+void memunmap_device_private_pagemap(struct dev_pagemap *pgmap);
+int devm_memremap_device_private_pagemap(struct device *dev, struct dev_pagemap *pgmap);
+void devm_memunmap_device_private_pagemap(struct device *dev, struct dev_pagemap *pgmap);
 void *memremap_pages(struct dev_pagemap *pgmap, int nid);
 void memunmap_pages(struct dev_pagemap *pgmap);
 void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap);
@@ -234,6 +248,15 @@ bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
 
 unsigned long memremap_compat_align(void);
 
+struct page *device_private_offset_to_page(unsigned long offset);
+struct page *device_private_entry_to_page(softleaf_t entry);
+pgoff_t device_private_page_to_offset(const struct page *page);
+
+static inline pgoff_t device_private_folio_to_offset(const struct folio *folio)
+{
+	return device_private_page_to_offset((const struct page *)&folio->page);
+}
+
 static inline void zone_device_folio_init(struct folio *folio, unsigned int order)
 {
 	zone_device_page_init(&folio->page, order);
@@ -276,6 +299,23 @@ static inline void devm_memunmap_pages(struct device *dev,
 {
 }
 
+static inline int devm_memremap_device_private_pagemap(struct device *dev,
+		struct dev_pagemap *pgmap)
+{
+	/*
+	 * Fail attempts to call devm_memremap_device_private_pagemap() without
+	 * ZONE_DEVICE support enabled, this requires callers to fall
+	 * back to plain devm_memremap() based on config
+	 */
+	WARN_ON_ONCE(1);
+	return -ENXIO;
+}
+
+static inline void devm_memunmap_device_private_pagemap(struct device *dev,
+		struct dev_pagemap *pgmap)
+{
+}
+
 static inline struct dev_pagemap *get_dev_pagemap(unsigned long pfn)
 {
 	return NULL;
@@ -296,6 +336,26 @@ static inline void zone_device_private_split_cb(struct folio *original_folio,
 						struct folio *new_folio)
 {
 }
+
+static inline struct page *device_private_offset_to_page(unsigned long offset)
+{
+	return NULL;
+}
+
+static inline struct page *device_private_entry_to_page(softleaf_t entry)
+{
+	return NULL;
+}
+
+static inline pgoff_t device_private_page_to_offset(const struct page *page)
+{
+	return 0;
+}
+
+static inline pgoff_t device_private_folio_to_offset(const struct folio *folio)
+{
+	return 0;
+}
 #endif /* CONFIG_ZONE_DEVICE */
 
 static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 52f65cd5c932..e6c4ff61a8fb 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -133,6 +133,10 @@ static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
 {
 	if (!(mpfn & MIGRATE_PFN_VALID))
 		return NULL;
+
+	if (mpfn & MIGRATE_PFN_DEVICE)
+		return device_private_offset_to_page(mpfn >> MIGRATE_PFN_SHIFT);
+
 	return pfn_to_page(mpfn >> MIGRATE_PFN_SHIFT);
 }
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index e65329e1969f..b36599ab41ba 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2038,6 +2038,8 @@ static inline unsigned long memdesc_section(memdesc_flags_t mdf)
  */
 static inline unsigned long folio_pfn(const struct folio *folio)
 {
+	VM_BUG_ON(folio_is_device_private(folio));
+
 	return page_to_pfn(&folio->page);
 }
 
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 57c63b6a8f65..c1561a92864f 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -951,7 +951,7 @@ static inline unsigned long page_vma_walk_pfn(unsigned long pfn)
 static inline unsigned long folio_page_vma_walk_pfn(const struct folio *folio)
 {
 	if (folio_is_device_private(folio))
-		return page_vma_walk_pfn(folio_pfn(folio)) |
+		return page_vma_walk_pfn(device_private_folio_to_offset(folio)) |
 		       PVMW_PFN_DEVICE_PRIVATE;
 
 	return page_vma_walk_pfn(folio_pfn(folio));
@@ -959,6 +959,9 @@ static inline unsigned long folio_page_vma_walk_pfn(const struct folio *folio)
 
 static inline struct page *page_vma_walk_pfn_to_page(unsigned long pvmw_pfn)
 {
+	if (pvmw_pfn & PVMW_PFN_DEVICE_PRIVATE)
+		return device_private_offset_to_page(pvmw_pfn >> PVMW_PFN_SHIFT);
+
 	return pfn_to_page(pvmw_pfn >> PVMW_PFN_SHIFT);
 }
 
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index ddf2763d69e9..9d6de68a823b 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -140,7 +140,7 @@ static inline swp_entry_t make_readable_device_private_entry(pgoff_t offset)
 
 static inline swp_entry_t make_readable_device_private_entry_from_page(struct page *page)
 {
-	return swp_entry(SWP_DEVICE_READ, page_to_pfn(page));
+	return swp_entry(SWP_DEVICE_READ, device_private_page_to_offset(page));
 }
 
 static inline swp_entry_t make_writable_device_private_entry(pgoff_t offset)
@@ -150,7 +150,7 @@ static inline swp_entry_t make_writable_device_private_entry(pgoff_t offset)
 
 static inline swp_entry_t make_writable_device_private_entry_from_page(struct page *page)
 {
-	return swp_entry(SWP_DEVICE_WRITE, page_to_pfn(page));
+	return swp_entry(SWP_DEVICE_WRITE, device_private_page_to_offset(page));
 }
 
 static inline swp_entry_t make_device_exclusive_entry(pgoff_t offset)
@@ -263,7 +263,8 @@ static inline swp_entry_t make_readable_migration_entry(pgoff_t offset)
 static inline swp_entry_t make_readable_migration_entry_from_page(struct page *page)
 {
 	if (is_device_private_page(page))
-		return make_readable_migration_device_private_entry(page_to_pfn(page));
+		return make_readable_migration_device_private_entry(
+				device_private_page_to_offset(page));
 
 	return swp_entry(SWP_MIGRATION_READ, page_to_pfn(page));
 }
@@ -276,7 +277,8 @@ static inline swp_entry_t make_readable_exclusive_migration_entry(pgoff_t offset
 static inline swp_entry_t make_readable_exclusive_migration_entry_from_page(struct page *page)
 {
 	if (is_device_private_page(page))
-		return make_readable_exclusive_migration_device_private_entry(page_to_pfn(page));
+		return make_readable_exclusive_migration_device_private_entry(
+				device_private_page_to_offset(page));
 
 	return swp_entry(SWP_MIGRATION_READ_EXCLUSIVE, page_to_pfn(page));
 }
@@ -289,7 +291,8 @@ static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
 static inline swp_entry_t make_writable_migration_entry_from_page(struct page *page)
 {
 	if (is_device_private_page(page))
-		return make_writable_migration_device_private_entry(page_to_pfn(page));
+		return make_writable_migration_device_private_entry(
+				device_private_page_to_offset(page));
 
 	return swp_entry(SWP_MIGRATION_WRITE, page_to_pfn(page));
 }
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 19681904a666..ac6649c7d7f7 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -497,7 +497,7 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 				  struct page **ppage, bool is_large)
 {
 	struct dmirror_chunk *devmem;
-	struct resource *res = NULL;
+	bool device_private = false;
 	unsigned long pfn;
 	unsigned long pfn_first;
 	unsigned long pfn_last;
@@ -510,13 +510,9 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 
 	switch (mdevice->zone_device_type) {
 	case HMM_DMIRROR_MEMORY_DEVICE_PRIVATE:
-		res = request_free_mem_region(&iomem_resource, DEVMEM_CHUNK_SIZE,
-					      "hmm_dmirror");
-		if (IS_ERR_OR_NULL(res))
-			goto err_devmem;
-		devmem->pagemap.range.start = res->start;
-		devmem->pagemap.range.end = res->end;
+		device_private = true;
 		devmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
+		devmem->pagemap.nr_pages = DEVMEM_CHUNK_SIZE / PAGE_SIZE;
 		break;
 	case HMM_DMIRROR_MEMORY_DEVICE_COHERENT:
 		devmem->pagemap.range.start = (MINOR(mdevice->cdevice.dev) - 2) ?
@@ -525,13 +521,13 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 		devmem->pagemap.range.end = devmem->pagemap.range.start +
 					    DEVMEM_CHUNK_SIZE - 1;
 		devmem->pagemap.type = MEMORY_DEVICE_COHERENT;
+		devmem->pagemap.nr_range = 1;
 		break;
 	default:
 		ret = -EINVAL;
 		goto err_devmem;
 	}
 
-	devmem->pagemap.nr_range = 1;
 	devmem->pagemap.ops = &dmirror_devmem_ops;
 	devmem->pagemap.owner = mdevice;
 
@@ -551,13 +547,20 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 		mdevice->devmem_capacity = new_capacity;
 		mdevice->devmem_chunks = new_chunks;
 	}
-	ptr = memremap_pages(&devmem->pagemap, numa_node_id());
-	if (IS_ERR_OR_NULL(ptr)) {
-		if (ptr)
-			ret = PTR_ERR(ptr);
-		else
-			ret = -EFAULT;
-		goto err_release;
+
+	if (device_private) {
+		ret = memremap_device_private_pagemap(&devmem->pagemap, numa_node_id());
+		if (ret)
+			goto err_release;
+	} else {
+		ptr = memremap_pages(&devmem->pagemap, numa_node_id());
+		if (IS_ERR_OR_NULL(ptr)) {
+			if (ptr)
+				ret = PTR_ERR(ptr);
+			else
+				ret = -EFAULT;
+			goto err_release;
+		}
 	}
 
 	devmem->mdevice = mdevice;
@@ -567,15 +570,21 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 
 	mutex_unlock(&mdevice->devmem_lock);
 
-	pr_info("added new %u MB chunk (total %u chunks, %u MB) PFNs [0x%lx 0x%lx)\n",
+	pr_info("added new %u MB chunk (total %u chunks, %u MB) %sPFNs [0x%lx 0x%lx)\n",
 		DEVMEM_CHUNK_SIZE / (1024 * 1024),
 		mdevice->devmem_count,
 		mdevice->devmem_count * (DEVMEM_CHUNK_SIZE / (1024 * 1024)),
+		device_private ? "device " : "",
 		pfn_first, pfn_last);
 
 	spin_lock(&mdevice->lock);
 	for (pfn = pfn_first; pfn < pfn_last; ) {
-		struct page *page = pfn_to_page(pfn);
+		struct page *page;
+
+		if (device_private)
+			page = device_private_offset_to_page(pfn);
+		else
+			page = pfn_to_page(pfn);
 
 		if (is_large && IS_ALIGNED(pfn, HPAGE_PMD_NR)
 			&& (pfn + HPAGE_PMD_NR <= pfn_last)) {
@@ -616,9 +625,6 @@ static int dmirror_allocate_chunk(struct dmirror_device *mdevice,
 
 err_release:
 	mutex_unlock(&mdevice->devmem_lock);
-	if (res && devmem->pagemap.type == MEMORY_DEVICE_PRIVATE)
-		release_mem_region(devmem->pagemap.range.start,
-				   range_len(&devmem->pagemap.range));
 err_devmem:
 	kfree(devmem);
 
@@ -696,8 +702,8 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 		 */
 		spage = migrate_pfn_to_page(*src);
 		if (WARN(spage && is_zone_device_page(spage),
-		     "page already in device spage pfn: 0x%lx\n",
-		     page_to_pfn(spage)))
+		     "page already in device spage dev pfn: 0x%lx\n",
+		     device_private_page_to_offset(spage)))
 			goto next;
 
 		if (dmirror->flags & HMM_DMIRROR_FLAG_FAIL_ALLOC) {
@@ -727,7 +733,9 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 				rpage = BACKING_PAGE(dpage);
 				rpage->zone_device_data = dmirror;
 
-				*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;
+				*dst = migrate_pfn(device_private_page_to_offset(dpage)) |
+				       MIGRATE_PFN_DEVICE |
+				       write;
 				src_page = pfn_to_page(spfn + i);
 
 				if (spage)
@@ -752,9 +760,10 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 		rpage->zone_device_data = dmirror;
 
 		pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
-			 page_to_pfn(spage), page_to_pfn(dpage));
+			 page_to_pfn(spage),
+			 device_private_page_to_offset(dpage));
 
-		*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;
+		*dst = migrate_pfn(device_private_page_to_offset(dpage)) | MIGRATE_PFN_DEVICE | write;
 
 		if (is_large) {
 			int i;
@@ -1457,10 +1466,10 @@ static void dmirror_device_remove_chunks(struct dmirror_device *mdevice)
 			spin_unlock(&mdevice->lock);
 
 			dmirror_device_evict_chunk(devmem);
-			memunmap_pages(&devmem->pagemap);
 			if (devmem->pagemap.type == MEMORY_DEVICE_PRIVATE)
-				release_mem_region(devmem->pagemap.range.start,
-						   range_len(&devmem->pagemap.range));
+				memunmap_device_private_pagemap(&devmem->pagemap);
+			else
+				memunmap_pages(&devmem->pagemap);
 			kfree(devmem);
 		}
 		mdevice->devmem_count = 0;
@@ -1705,7 +1714,12 @@ static void dmirror_devmem_folio_split(struct folio *head, struct folio *tail)
 		return;
 	}
 
-	offset = folio_pfn(tail) - folio_pfn(head);
+	tail->pgmap = head->pgmap;
+
+	if (folio_is_device_private(head))
+		offset = device_private_folio_to_offset(tail) - device_private_folio_to_offset(head);
+	else
+		offset = folio_pfn(tail) - folio_pfn(head);
 
 	rpage_tail = folio_page(rfolio, offset);
 	tail->page.zone_device_data = rpage_tail;
@@ -1714,7 +1728,6 @@ static void dmirror_devmem_folio_split(struct folio *head, struct folio *tail)
 	rpage_tail->mapping = NULL;
 
 	folio_page(tail, 0)->mapping = folio_page(head, 0)->mapping;
-	tail->pgmap = head->pgmap;
 	folio_set_count(page_folio(rpage_tail), 1);
 }
 
diff --git a/mm/debug.c b/mm/debug.c
index 77fa8fe1d641..04fcc62d440f 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -77,9 +77,11 @@ static void __dump_folio(const struct folio *folio, const struct page *page,
 	if (page_mapcount_is_type(mapcount))
 		mapcount = 0;
 
-	pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx pfn:%#lx\n",
+	pr_warn("page: refcount:%d mapcount:%d mapping:%p index:%#lx %spfn:%#lx\n",
 			folio_ref_count(folio), mapcount, mapping,
-			folio->index + idx, pfn);
+			folio->index + idx,
+			folio_is_device_private(folio) ? "device " : "",
+			pfn);
 	if (folio_test_large(folio)) {
 		int pincount = 0;
 
@@ -113,7 +115,8 @@ static void __dump_folio(const struct folio *folio, const struct page *page,
 	 * inaccuracy here due to racing.
 	 */
 	pr_warn("%sflags: %pGp%s\n", type, &folio->flags,
-		is_migrate_cma_folio(folio, pfn) ? " CMA" : "");
+		(!folio_is_device_private(folio) &&
+		 is_migrate_cma_folio(folio, pfn)) ? " CMA" : "");
 	if (page_has_type(&folio->page))
 		pr_warn("page_type: %x(%s)\n", folio->page.page_type >> 24,
 				page_type_name(folio->page.page_type));
diff --git a/mm/memremap.c b/mm/memremap.c
index 4c2e0d68eb27..f0fe92c3227a 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -12,9 +12,12 @@
 #include <linux/types.h>
 #include <linux/wait_bit.h>
 #include <linux/xarray.h>
+#include <linux/maple_tree.h>
 #include "internal.h"
 
 static DEFINE_XARRAY(pgmap_array);
+static struct maple_tree device_private_pgmap_tree =
+	MTREE_INIT(device_private_pgmap_tree, MT_FLAGS_ALLOC_RANGE);
 
 /*
  * The memremap() and memremap_pages() interfaces are alternately used
@@ -113,9 +116,10 @@ void memunmap_pages(struct dev_pagemap *pgmap)
 {
 	int i;
 
+	WARN_ONCE(pgmap->type == MEMORY_DEVICE_PRIVATE, "Type should not be MEMORY_DEVICE_PRIVATE\n");
+
 	percpu_ref_kill(&pgmap->ref);
-	if (pgmap->type != MEMORY_DEVICE_PRIVATE &&
-	    pgmap->type != MEMORY_DEVICE_COHERENT)
+	if (pgmap->type != MEMORY_DEVICE_COHERENT)
 		for (i = 0; i < pgmap->nr_range; i++)
 			percpu_ref_put_many(&pgmap->ref, pfn_len(pgmap, i));
 
@@ -144,7 +148,6 @@ static void dev_pagemap_percpu_release(struct percpu_ref *ref)
 static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
 		int range_id, int nid)
 {
-	const bool is_private = pgmap->type == MEMORY_DEVICE_PRIVATE;
 	struct range *range = &pgmap->ranges[range_id];
 	struct dev_pagemap *conflict_pgmap;
 	int error, is_ram;
@@ -190,7 +193,7 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
 	if (error)
 		goto err_pfn_remap;
 
-	if (!mhp_range_allowed(range->start, range_len(range), !is_private)) {
+	if (!mhp_range_allowed(range->start, range_len(range), true)) {
 		error = -EINVAL;
 		goto err_kasan;
 	}
@@ -198,30 +201,19 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
 	mem_hotplug_begin();
 
 	/*
-	 * For device private memory we call add_pages() as we only need to
-	 * allocate and initialize struct page for the device memory. More-
-	 * over the device memory is un-accessible thus we do not want to
-	 * create a linear mapping for the memory like arch_add_memory()
-	 * would do.
-	 *
-	 * For all other device memory types, which are accessible by
-	 * the CPU, we do want the linear mapping and thus use
+	 * All device memory types except device private memory are accessible
+	 * by the CPU, so we want the linear mapping and thus use
 	 * arch_add_memory().
 	 */
-	if (is_private) {
-		error = add_pages(nid, PHYS_PFN(range->start),
-				PHYS_PFN(range_len(range)), params);
-	} else {
-		error = kasan_add_zero_shadow(__va(range->start), range_len(range));
-		if (error) {
-			mem_hotplug_done();
-			goto err_kasan;
-		}
-
-		error = arch_add_memory(nid, range->start, range_len(range),
-					params);
+	error = kasan_add_zero_shadow(__va(range->start), range_len(range));
+	if (error) {
+		mem_hotplug_done();
+		goto err_kasan;
 	}
 
+	error = arch_add_memory(nid, range->start, range_len(range),
+				params);
+
 	if (!error) {
 		struct zone *zone;
 
@@ -248,8 +240,7 @@ static int pagemap_range(struct dev_pagemap *pgmap, struct mhp_params *params,
 	return 0;
 
 err_add_memory:
-	if (!is_private)
-		kasan_remove_zero_shadow(__va(range->start), range_len(range));
+	kasan_remove_zero_shadow(__va(range->start), range_len(range));
 err_kasan:
 	pfnmap_untrack(PHYS_PFN(range->start), range_len(range));
 err_pfn_remap:
@@ -281,22 +272,8 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 
 	switch (pgmap->type) {
 	case MEMORY_DEVICE_PRIVATE:
-		if (!IS_ENABLED(CONFIG_DEVICE_PRIVATE)) {
-			WARN(1, "Device private memory not supported\n");
-			return ERR_PTR(-EINVAL);
-		}
-		if (!pgmap->ops || !pgmap->ops->migrate_to_ram) {
-			WARN(1, "Missing migrate_to_ram method\n");
-			return ERR_PTR(-EINVAL);
-		}
-		if (!pgmap->ops->folio_free) {
-			WARN(1, "Missing folio_free method\n");
-			return ERR_PTR(-EINVAL);
-		}
-		if (!pgmap->owner) {
-			WARN(1, "Missing owner\n");
-			return ERR_PTR(-EINVAL);
-		}
+		WARN(1, "Use memremap_device_private_pagemap()\n");
+		return ERR_PTR(-EINVAL);
 		break;
 	case MEMORY_DEVICE_COHERENT:
 		if (!pgmap->ops->folio_free) {
@@ -394,6 +371,31 @@ void devm_memunmap_pages(struct device *dev, struct dev_pagemap *pgmap)
 }
 EXPORT_SYMBOL_GPL(devm_memunmap_pages);
 
+static void devm_memremap_device_private_pagemap_release(void *data)
+{
+	memunmap_device_private_pagemap(data);
+}
+
+int devm_memremap_device_private_pagemap(struct device *dev, struct dev_pagemap *pgmap)
+{
+	int ret;
+
+	ret = memremap_device_private_pagemap(pgmap, dev_to_node(dev));
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(dev, devm_memremap_device_private_pagemap_release,
+			pgmap);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(devm_memremap_device_private_pagemap);
+
+void devm_memunmap_device_private_pagemap(struct device *dev, struct dev_pagemap *pgmap)
+{
+	devm_release_action(dev, devm_memremap_device_private_pagemap_release, pgmap);
+}
+EXPORT_SYMBOL_GPL(devm_memunmap_device_private_pagemap);
+
 /**
  * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
  * @pfn: page frame number to lookup page_map
@@ -495,3 +497,110 @@ void zone_device_page_init(struct page *page, unsigned int order)
 		prep_compound_page(page, order);
 }
 EXPORT_SYMBOL_GPL(zone_device_page_init);
+
+unsigned long memremap_device_private_pagemap(struct dev_pagemap *pgmap, int nid)
+{
+	unsigned long dpfn, dpfn_first, dpfn_last = 0;
+	unsigned long start;
+	int rc;
+
+	if (pgmap->type != MEMORY_DEVICE_PRIVATE) {
+		WARN(1, "Not device private memory\n");
+		return -EINVAL;
+	}
+	if (!IS_ENABLED(CONFIG_DEVICE_PRIVATE)) {
+		WARN(1, "Device private memory not supported\n");
+		return -EINVAL;
+	}
+	if (!pgmap->ops || !pgmap->ops->migrate_to_ram) {
+		WARN(1, "Missing migrate_to_ram method\n");
+		return -EINVAL;
+	}
+	if (!pgmap->owner) {
+		WARN(1, "Missing owner\n");
+		return -EINVAL;
+	}
+
+	pgmap->pages = kvzalloc(sizeof(struct page) * pgmap->nr_pages,
+			       GFP_KERNEL);
+	if (!pgmap->pages)
+		return -ENOMEM;
+
+	rc = mtree_alloc_range(&device_private_pgmap_tree, &start, pgmap,
+			       pgmap->nr_pages * PAGE_SIZE, 0,
+			       1ull << MAX_PHYSMEM_BITS, GFP_KERNEL);
+	if (rc < 0)
+		goto err_mtree_alloc;
+
+	pgmap->range.start = start;
+	pgmap->range.end = pgmap->range.start + (pgmap->nr_pages * PAGE_SIZE) - 1;
+	pgmap->nr_range = 1;
+
+	init_completion(&pgmap->done);
+	rc = percpu_ref_init(&pgmap->ref, dev_pagemap_percpu_release, 0,
+		GFP_KERNEL);
+	if (rc < 0)
+		goto err_ref_init;
+
+	dpfn_first = pgmap->range.start >> PAGE_SHIFT;
+	dpfn_last = dpfn_first + (range_len(&pgmap->range) >> PAGE_SHIFT);
+	for (dpfn = dpfn_first; dpfn < dpfn_last; dpfn++) {
+		struct page *page = device_private_offset_to_page(dpfn);
+
+		__init_zone_device_page(page, dpfn, ZONE_DEVICE, nid, pgmap);
+		page_folio(page)->pgmap = (void *) pgmap;
+	}
+
+	return 0;
+
+err_ref_init:
+	mtree_erase(&device_private_pgmap_tree, pgmap->range.start);
+err_mtree_alloc:
+	kvfree(pgmap->pages);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(memremap_device_private_pagemap);
+
+void memunmap_device_private_pagemap(struct dev_pagemap *pgmap)
+{
+	percpu_ref_kill(&pgmap->ref);
+	wait_for_completion(&pgmap->done);
+	percpu_ref_exit(&pgmap->ref);
+	kvfree(pgmap->pages);
+	mtree_erase(&device_private_pgmap_tree, pgmap->range.start);
+}
+EXPORT_SYMBOL_GPL(memunmap_device_private_pagemap);
+
+struct page *device_private_offset_to_page(unsigned long offset)
+{
+	struct dev_pagemap *pgmap;
+
+	pgmap = mtree_load(&device_private_pgmap_tree, offset << PAGE_SHIFT);
+	if (WARN_ON_ONCE(!pgmap))
+		return NULL;
+
+	return &pgmap->pages[offset - (pgmap->range.start >> PAGE_SHIFT)];
+}
+EXPORT_SYMBOL_GPL(device_private_offset_to_page);
+
+struct page *device_private_entry_to_page(softleaf_t entry)
+{
+	unsigned long offset;
+
+	if (!((softleaf_is_device_private(entry) ||
+	    (softleaf_is_migration_device_private(entry)))))
+		return NULL;
+
+	offset = softleaf_to_pfn(entry);
+	return device_private_offset_to_page(offset);
+}
+
+pgoff_t device_private_page_to_offset(const struct page *page)
+{
+	struct dev_pagemap *pgmap = (struct dev_pagemap *) page_pgmap(page);
+
+	VM_BUG_ON_PAGE(!is_device_private_page(page), page);
+
+	return (pgmap->range.start >> PAGE_SHIFT) + ((page - pgmap->pages));
+}
+EXPORT_SYMBOL_GPL(device_private_page_to_offset);
diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 5cc58a5876a0..db8058705994 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -200,6 +200,7 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
 		(IS_ALIGNED(start, HPAGE_PMD_SIZE) &&
 		 IS_ALIGNED(end, HPAGE_PMD_SIZE))) {
 		unsigned long device_private = 0;
+		unsigned long pfn;
 
 		struct page_vma_mapped_walk pvmw = {
 			.ptl = ptl,
@@ -208,9 +209,12 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
 			.vma = walk->vma,
 		};
 
-		unsigned long pfn = page_to_pfn(folio_page(folio, 0));
-		if (folio_is_device_private(folio))
+		if (folio_is_device_private(folio)) {
+			pfn = device_private_folio_to_offset(folio);
 			device_private = MIGRATE_PFN_DEVICE;
+		} else {
+			pfn = page_to_pfn(folio_page(folio, 0));
+		}
 
 		migrate->src[migrate->npages] = migrate_pfn(pfn) | write
 						| MIGRATE_PFN_MIGRATE
@@ -332,7 +336,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 				goto again;
 			}
 
-			mpfn = migrate_pfn(page_to_pfn(page)) |
+			mpfn = migrate_pfn(device_private_page_to_offset(page)) |
 					MIGRATE_PFN_MIGRATE |
 					MIGRATE_PFN_DEVICE;
 			if (softleaf_is_device_private_write(entry))
@@ -1360,7 +1364,7 @@ static unsigned long migrate_device_pfn_lock(unsigned long pfn)
 {
 	struct folio *folio;
 
-	folio = folio_get_nontail_page(pfn_to_page(pfn));
+	folio = folio_get_nontail_page(device_private_offset_to_page(pfn));
 	if (!folio)
 		return 0;
 
diff --git a/mm/mm_init.c b/mm/mm_init.c
index fc2a6f1e518f..4a9420cb610c 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1004,9 +1004,9 @@ static void __init memmap_init(void)
 }
 
 #ifdef CONFIG_ZONE_DEVICE
-static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
-					  unsigned long zone_idx, int nid,
-					  struct dev_pagemap *pgmap)
+void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
+				   unsigned long zone_idx, int nid,
+				   struct dev_pagemap *pgmap)
 {
 
 	__init_single_page(page, pfn, zone_idx, nid);
@@ -1038,7 +1038,7 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
 	 * Please note that MEMINIT_HOTPLUG path doesn't clear memmap
 	 * because this is done early in section_activate()
 	 */
-	if (pageblock_aligned(pfn)) {
+	if (pgmap->type != MEMORY_DEVICE_PRIVATE && pageblock_aligned(pfn)) {
 		init_pageblock_migratetype(page, MIGRATE_MOVABLE, false);
 		cond_resched();
 	}
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index b19820a51e95..141fe5abd33f 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -107,6 +107,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp,
 static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 {
 	unsigned long pfn;
+	bool device_private = false;
 	pte_t ptent = ptep_get(pvmw->pte);
 
 	if (pvmw->flags & PVMW_MIGRATION) {
@@ -115,6 +116,9 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 		if (!softleaf_is_migration(entry))
 			return false;
 
+		if (softleaf_is_migration_device_private(entry))
+			device_private = true;
+
 		pfn = softleaf_to_pfn(entry);
 	} else if (pte_present(ptent)) {
 		pfn = pte_pfn(ptent);
@@ -127,8 +131,14 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 			return false;
 
 		pfn = softleaf_to_pfn(entry);
+
+		if (softleaf_is_device_private(entry))
+			device_private = true;
 	}
 
+	if ((device_private) ^ !!(pvmw->pfn & PVMW_PFN_DEVICE_PRIVATE))
+		return false;
+
 	if ((pfn + pte_nr - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
 		return false;
 	if (pfn > ((pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1))
@@ -139,6 +149,9 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw, unsigned long pte_nr)
 /* Returns true if the two ranges overlap.  Careful to not overflow. */
 static bool check_pmd(unsigned long pfn, bool device_private, struct page_vma_mapped_walk *pvmw)
 {
+	if ((device_private) ^ !!(pvmw->pfn & PVMW_PFN_DEVICE_PRIVATE))
+		return false;
+
 	if ((pfn + HPAGE_PMD_NR - 1) < (pvmw->pfn >> PVMW_PFN_SHIFT))
 		return false;
 	if (pfn > (pvmw->pfn >> PVMW_PFN_SHIFT) + pvmw->nr_pages - 1)
diff --git a/mm/rmap.c b/mm/rmap.c
index bb881b0c4b06..04d74579d1b1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1860,7 +1860,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 	struct mmu_notifier_range range;
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
 	unsigned long nr_pages = 1, end_addr;
-	unsigned long pfn;
+	unsigned long nr;
 	unsigned long hsz = 0;
 	int ptes = 0;
 
@@ -1967,15 +1967,20 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		pteval = ptep_get(pvmw.pte);
 		if (likely(pte_present(pteval))) {
-			pfn = pte_pfn(pteval);
+			nr = pte_pfn(pteval) - folio_pfn(folio);
 		} else {
 			const softleaf_t entry = softleaf_from_pte(pteval);
 
-			pfn = softleaf_to_pfn(entry);
+			if (softleaf_is_device_private(entry) ||
+			    softleaf_is_migration_device_private(entry))
+				nr = softleaf_to_pfn(entry) - device_private_folio_to_offset(folio);
+			else
+				nr = softleaf_to_pfn(entry) - folio_pfn(folio);
+
 			VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
 		}
 
-		subpage = folio_page(folio, pfn - folio_pfn(folio));
+		subpage = folio_page(folio, nr);
 		address = pvmw.address;
 		anon_exclusive = folio_test_anon(folio) &&
 				 PageAnonExclusive(subpage);
@@ -2289,7 +2294,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 	struct page *subpage;
 	struct mmu_notifier_range range;
 	enum ttu_flags flags = (enum ttu_flags)(long)arg;
-	unsigned long pfn;
+	unsigned long nr;
 	unsigned long hsz = 0;
 
 	/*
@@ -2328,7 +2333,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 	while (page_vma_mapped_walk(&pvmw)) {
 		/* PMD-mapped THP migration entry */
 		if (!pvmw.pte) {
-			__maybe_unused unsigned long pfn;
+			__maybe_unused softleaf_t entry;
 			__maybe_unused pmd_t pmdval;
 
 			if (flags & TTU_SPLIT_HUGE_PMD) {
@@ -2340,12 +2345,17 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 			}
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 			pmdval = pmdp_get(pvmw.pmd);
+			entry = softleaf_from_pmd(pmdval);
 			if (likely(pmd_present(pmdval)))
-				pfn = pmd_pfn(pmdval);
-			else
-				pfn = softleaf_to_pfn(softleaf_from_pmd(pmdval));
+				nr = pmd_pfn(pmdval) - folio_pfn(folio);
+			else if (softleaf_is_device_private(entry) ||
+				 softleaf_is_migration_device_private(entry)) {
+				nr = softleaf_to_pfn(entry) - device_private_folio_to_offset(folio);
+			} else {
+				nr = softleaf_to_pfn(entry) - folio_pfn(folio);
+			}
 
-			subpage = folio_page(folio, pfn - folio_pfn(folio));
+			subpage = folio_page(folio, nr);
 
 			VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
 					!folio_test_pmd_mappable(folio), folio);
@@ -2368,15 +2378,20 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		pteval = ptep_get(pvmw.pte);
 		if (likely(pte_present(pteval))) {
-			pfn = pte_pfn(pteval);
+			nr = pte_pfn(pteval) - folio_pfn(folio);
 		} else {
 			const softleaf_t entry = softleaf_from_pte(pteval);
 
-			pfn = softleaf_to_pfn(entry);
+			if (softleaf_is_device_private(entry) ||
+			    is_device_private_migration_entry(entry))
+				nr = softleaf_to_pfn(entry) - device_private_folio_to_offset(folio);
+			else
+				nr = softleaf_to_pfn(entry) - folio_pfn(folio);
+
 			VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio);
 		}
 
-		subpage = folio_page(folio, pfn - folio_pfn(folio));
+		subpage = folio_page(folio, nr);
 		address = pvmw.address;
 		anon_exclusive = folio_test_anon(folio) &&
 				 PageAnonExclusive(subpage);
@@ -2436,7 +2451,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 				folio_mark_dirty(folio);
 			writable = pte_write(pteval);
 		} else if (likely(pte_present(pteval))) {
-			flush_cache_page(vma, address, pfn);
+			flush_cache_page(vma, address, pte_pfn(pteval));
 			/* Nuke the page table entry. */
 			if (should_defer_flush(mm, flags)) {
 				/*
diff --git a/mm/util.c b/mm/util.c
index 65e3f1a97d76..8482ebc5c394 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1244,7 +1244,10 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
 	struct folio *foliop;
 	int loops = 5;
 
-	ps->pfn = page_to_pfn(page);
+	if (is_device_private_page(page))
+		ps->pfn = device_private_page_to_offset(page);
+	else
+		ps->pfn = page_to_pfn(page);
 	ps->flags = PAGE_SNAPSHOT_FAITHFUL;
 
 again:
-- 
2.34.1

Re: [PATCH v1 1/8] mm/migrate_device: Add migrate PFN flag to track device private pages

[Kuehling, Felix]

On 2025-12-30 23:31, Jordan Niethe wrote:
> A future change will remove device private pages from the physical
> address space. This will mean that device private pages no longer have
> normal PFN and must be handled separately.
>
> Prepare for this by adding a MIGRATE_PFN_DEVICE flag to indicate
> that a migrate pfn contains a PFN for a device private page.

Thanks for doing this. Some comments inline regarding DEVICE_COHERENT 
pages. I suspect this will have ripple effects on the rest of the patch 
series, at least in patch 8, but I haven't looked at that in detail yet.


>
> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>
>
> ---
> v1:
> - Update for HMM huge page support
> - Update existing drivers to use MIGRATE_PFN_DEVICE
> ---
>   arch/powerpc/kvm/book3s_hv_uvmem.c       |  2 +-
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  3 ++-
>   drivers/gpu/drm/drm_pagemap.c            |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_dmem.c   |  2 +-
>   include/linux/migrate.h                  |  1 +
>   lib/test_hmm.c                           |  4 ++--
>   mm/migrate_device.c                      | 11 ++++++++---
>   7 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index e5000bef90f2..dac5d6454920 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -784,7 +784,7 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma,
>   		}
>   	}
>   
> -	*mig.dst = migrate_pfn(page_to_pfn(dpage));
> +	*mig.dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
>   	migrate_vma_pages(&mig);
>   out_finalize:
>   	migrate_vma_finalize(&mig);
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index af53e796ea1b..0257c6e7f680 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -303,7 +303,8 @@ svm_migrate_copy_to_vram(struct kfd_node *node, struct svm_range *prange,
>   			dst[i] = cursor.start + (j << PAGE_SHIFT);
>   			migrate->dst[i] = svm_migrate_addr_to_pfn(adev, dst[i]);
>   			svm_migrate_get_vram_page(prange, migrate->dst[i]);
> -			migrate->dst[i] = migrate_pfn(migrate->dst[i]);
> +			migrate->dst[i] = migrate_pfn(migrate->dst[i]) |
> +					  MIGRATE_PFN_DEVICE;

On some of our GPUs we use DEVICE_COHERENT pages. These are pages that 
are coherently accessible by the CPU and peer devices in the system 
physical address space. Therefore, this needs to be conditional. Maybe 
add something like adev->kfd.migrate_pfn_flag that gets initialized 
conditionally in kgd2kfd_init_zone_device. Then add ... | 
adev->kfd.migrate_pfn_flag here.


>   			mpages++;
>   		}
>   		spage = migrate_pfn_to_page(migrate->src[i]);
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 37d7cfbbb3e8..0c756d73419f 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -404,7 +404,7 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>   		struct page *page = pfn_to_page(migrate.dst[i]);
>   
>   		pages[i] = page;
> -		migrate.dst[i] = migrate_pfn(migrate.dst[i]);
> +		migrate.dst[i] = migrate_pfn(migrate.dst[i]) | MIGRATE_PFN_DEVICE;
>   		drm_pagemap_get_devmem_page(page, zdd);
>   	}
>   
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 58071652679d..2bd80c6f5bcd 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -766,7 +766,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
>   		((paddr >> PAGE_SHIFT) << NVIF_VMM_PFNMAP_V0_ADDR_SHIFT);
>   	if (src & MIGRATE_PFN_WRITE)
>   		*pfn |= NVIF_VMM_PFNMAP_V0_W;
> -	mpfn = migrate_pfn(page_to_pfn(dpage));
> +	mpfn = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE;
>   	if (folio_order(page_folio(dpage)))
>   		mpfn |= MIGRATE_PFN_COMPOUND;
>   	return mpfn;
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 26ca00c325d9..52f65cd5c932 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -126,6 +126,7 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
>   #define MIGRATE_PFN_MIGRATE	(1UL << 1)
>   #define MIGRATE_PFN_WRITE	(1UL << 3)
>   #define MIGRATE_PFN_COMPOUND	(1UL << 4)
> +#define MIGRATE_PFN_DEVICE	(1UL << 5)
>   #define MIGRATE_PFN_SHIFT	6
>   
>   static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 8af169d3873a..19681904a666 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -727,7 +727,7 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
>   				rpage = BACKING_PAGE(dpage);
>   				rpage->zone_device_data = dmirror;
>   
> -				*dst = migrate_pfn(page_to_pfn(dpage)) | write;
> +				*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;

This needs to be conditional on dmirror->mdevice->zone_device_type.


>   				src_page = pfn_to_page(spfn + i);
>   
>   				if (spage)
> @@ -754,7 +754,7 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
>   		pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
>   			 page_to_pfn(spage), page_to_pfn(dpage));
>   
> -		*dst = migrate_pfn(page_to_pfn(dpage)) | write;
> +		*dst = migrate_pfn(page_to_pfn(dpage)) | MIGRATE_PFN_DEVICE | write;

Same here.


>   
>   		if (is_large) {
>   			int i;
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index 23379663b1e1..5d108ddf1a97 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -199,6 +199,7 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
>   		(migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) &&
>   		(IS_ALIGNED(start, HPAGE_PMD_SIZE) &&
>   		 IS_ALIGNED(end, HPAGE_PMD_SIZE))) {
> +		unsigned long device_private = 0;
>   
>   		struct page_vma_mapped_walk pvmw = {
>   			.ptl = ptl,
> @@ -208,10 +209,13 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
>   		};
>   
>   		unsigned long pfn = page_to_pfn(folio_page(folio, 0));
> +		if (folio_is_device_private(folio))
> +			device_private = MIGRATE_PFN_DEVICE;
>   
>   		migrate->src[migrate->npages] = migrate_pfn(pfn) | write
>   						| MIGRATE_PFN_MIGRATE
> -						| MIGRATE_PFN_COMPOUND;
> +						| MIGRATE_PFN_COMPOUND
> +						| device_private;
>   		migrate->dst[migrate->npages++] = 0;
>   		migrate->cpages++;
>   		ret = set_pmd_migration_entry(&pvmw, folio_page(folio, 0));
> @@ -329,7 +333,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>   			}
>   
>   			mpfn = migrate_pfn(page_to_pfn(page)) |
> -					MIGRATE_PFN_MIGRATE;
> +					MIGRATE_PFN_MIGRATE |
> +					MIGRATE_PFN_DEVICE;

I think this also needs to be conditional to distinguish DEVICE_COHERENT 
pages.


>   			if (softleaf_is_device_private_write(entry))
>   				mpfn |= MIGRATE_PFN_WRITE;
>   		} else {
> @@ -1368,7 +1373,7 @@ static unsigned long migrate_device_pfn_lock(unsigned long pfn)
>   		return 0;
>   	}
>   
> -	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
> +	return migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE | MIGRATE_PFN_DEVICE;

Same here.

Regards,
   Felix


>   }
>   
>   /**