Re: [PATCH v3 04/13] mm/migrate_device: Add migrate PFN flag to track device private pages

["Kuehling, Felix" <felix.kuehling@amd.com>]

On 2026-01-23 01:23, 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_PRIVATE 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>

Acked-by: Felix Kuehling <felix.kuehling@amd.com>


>
> ---
> v1:
> - Update for HMM huge page support
> - Update existing drivers to use MIGRATE_PFN_DEVICE
> v2:
> - Include changes to migrate_pfn_from_page()
> - Rename to MIGRATE_PFN_DEVICE_PRIVATE
> - drm/amd: Check adev->gmc.xgmi.connected_to_cpu
> - lib/test_hmm.c: Check chunk->pagemap.type == MEMORY_DEVICE_PRIVATE
>
> v3:
> - Use adev->kfd.pgmap.type == MEMORY_DEVICE_PRIVATE
> ---
>   drivers/gpu/drm/amd/amdkfd/kfd_migrate.c |  7 ++++++-
>   drivers/gpu/drm/nouveau/nouveau_dmem.c   |  3 ++-
>   drivers/gpu/drm/xe/xe_svm.c              |  2 +-
>   include/linux/migrate.h                  | 14 +++++++++-----
>   lib/test_hmm.c                           |  6 +++++-
>   5 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index 3dd7a35d19f7..5478e41877e5 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -212,7 +212,12 @@ svm_migrate_copy_done(struct amdgpu_device *adev, struct dma_fence *mfence)
>   unsigned long
>   svm_migrate_addr_to_mpfn(struct amdgpu_device *adev, unsigned long addr)
>   {
> -	return migrate_pfn((addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT);
> +	unsigned long flags = 0;
> +
> +	if (adev->kfd.pgmap.type == MEMORY_DEVICE_PRIVATE)
> +		flags |= MIGRATE_PFN_DEVICE_PRIVATE;
> +	return migrate_pfn((addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT) |
> +	       flags;
>   }
>   
>   static void
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index bd3f7102c3f9..adfa3df5cbc5 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -484,7 +484,8 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
>   	dma_info = kvcalloc(npages, sizeof(*dma_info), GFP_KERNEL | __GFP_NOFAIL);
>   
>   	migrate_device_range(src_pfns,
> -			     migrate_pfn(chunk->pagemap.range.start >> PAGE_SHIFT),
> +			     migrate_pfn(chunk->pagemap.range.start >> PAGE_SHIFT) |
> +			     MIGRATE_PFN_DEVICE_PRIVATE,
>   			     npages);
>   
>   	for (i = 0; i < npages; i++) {
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index fbf5fd284616..a8aad9e0b1fb 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -770,7 +770,7 @@ static int xe_svm_populate_devmem_mpfn(struct drm_pagemap_devmem *devmem_allocat
>   		int i;
>   
>   		for (i = 0; i < drm_buddy_block_size(buddy, block) >> PAGE_SHIFT; ++i)
> -			pfn[j++] = migrate_pfn(block_pfn + i);
> +			pfn[j++] = migrate_pfn(block_pfn + i) | MIGRATE_PFN_DEVICE_PRIVATE;
>   	}
>   
>   	return 0;
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index d269ec1400be..5fd2ee080bc0 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -122,11 +122,12 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
>    * have enough bits to store all physical address and flags. So far we have
>    * enough room for all our flags.
>    */
> -#define MIGRATE_PFN_VALID	(1UL << 0)
> -#define MIGRATE_PFN_MIGRATE	(1UL << 1)
> -#define MIGRATE_PFN_WRITE	(1UL << 3)
> -#define MIGRATE_PFN_COMPOUND	(1UL << 4)
> -#define MIGRATE_PFN_SHIFT	6
> +#define MIGRATE_PFN_VALID		(1UL << 0)
> +#define MIGRATE_PFN_MIGRATE		(1UL << 1)
> +#define MIGRATE_PFN_WRITE		(1UL << 3)
> +#define MIGRATE_PFN_COMPOUND		(1UL << 4)
> +#define MIGRATE_PFN_DEVICE_PRIVATE	(1UL << 5)
> +#define MIGRATE_PFN_SHIFT		6
>   
>   static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
>   {
> @@ -142,6 +143,9 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
>   
>   static inline unsigned long migrate_pfn_from_page(struct page *page)
>   {
> +	if (is_device_private_page(page))
> +		return migrate_pfn(page_to_pfn(page)) |
> +		       MIGRATE_PFN_DEVICE_PRIVATE;
>   	return migrate_pfn(page_to_pfn(page));
>   }
>   
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index a6ff292596f3..872d3846af7b 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -1385,11 +1385,15 @@ static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
>   	unsigned long *src_pfns;
>   	unsigned long *dst_pfns;
>   	unsigned int order = 0;
> +	unsigned long flags = 0;
>   
>   	src_pfns = kvcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAIL);
>   	dst_pfns = kvcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAIL);
>   
> -	migrate_device_range(src_pfns, migrate_pfn(start_pfn), npages);
> +	if (chunk->pagemap.type == MEMORY_DEVICE_PRIVATE)
> +		flags |= MIGRATE_PFN_DEVICE_PRIVATE;
> +
> +	migrate_device_range(src_pfns, migrate_pfn(start_pfn) | flags, npages);
>   	for (i = 0; i < npages; i++) {
>   		struct page *dpage, *spage;
>