[PATCH] mm: use clear_user_(high)page() for arch with special user folio handling

[PATCH] mm: use clear_user_(high)page() for arch with special user folio handling

[Zi Yan]

For architectures setting ARCH_HAS_CPU_CACHE_ALIASING, which requires
flushing cache and arc, which sets folio->flags after clearing a user
folio, __GFP_ZERO, which uses only clear_page(), is not enough to zero
user folios and clear_user_(high)page() must be used. Otherwise, user data
will be corrupted.

Fix it by always clearing user folios with clear_user_(high)page() for
CONFIG_ARCH_HAS_CPU_CACHE_ALIASING || CONFIG_ARC. Rename alloc_zeroed()
to alloc_need_zeroing() and invert the logic to clarify its intend.

Fixes: 5708d96da20b ("mm: avoid zeroing user movable page twice with init_on_alloc=1")
Reported-by: Geert Uytterhoeven <geert+renesas@glider.be>
Closes: https://lore.kernel.org/linux-mm/CAMuHMdV1hRp_NtR5YnJo=HsfgKQeH91J537Gh4gKk3PFZhSkbA@mail.gmail.com/
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 include/linux/highmem.h |  8 +++++++-
 include/linux/mm.h      | 17 +++++++++++++++++
 mm/huge_memory.c        |  9 +++++----
 mm/internal.h           |  6 ------
 mm/memory.c             | 10 +++++-----
 5 files changed, 34 insertions(+), 16 deletions(-)

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 6e452bd8e7e3..d9beb8371daa 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -224,7 +224,13 @@ static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
 				   unsigned long vaddr)
 {
-	return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr);
+	struct folio *folio;
+
+	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
+	if (folio && alloc_need_zeroing())
+		clear_user_highpage(&folio->page, vaddr);
+
+	return folio;
 }
 #endif
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c39c4945946c..6ac0308c4380 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4175,6 +4175,23 @@ static inline int do_mseal(unsigned long start, size_t len_in, unsigned long fla
 }
 #endif
 
+/*
+ * alloc_need_zeroing checks if a user folio from page allocator needs to be
+ * zeroed or not.
+ */
+static inline bool alloc_need_zeroing(void)
+{
+	/*
+	 * for user folios, arch with cache aliasing requires cache flush and
+	 * arc sets folio->flags, so always return false to make caller use
+	 * clear_user_page()/clear_user_highpage()
+	 */
+	return (IS_ENABLED(CONFIG_ARCH_HAS_CPU_CACHE_ALIASING) ||
+		IS_ENABLED(CONFIG_ARC)) ||
+	       !static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
+				   &init_on_alloc);
+}
+
 int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *status);
 int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status);
 int arch_lock_shadow_stack_status(struct task_struct *t, unsigned long status);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ee335d96fc39..107130a5413a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1176,11 +1176,12 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
 	folio_throttle_swaprate(folio, gfp);
 
        /*
-	* When a folio is not zeroed during allocation (__GFP_ZERO not used),
-	* folio_zero_user() is used to make sure that the page corresponding
-	* to the faulting address will be hot in the cache after zeroing.
+	* When a folio is not zeroed during allocation (__GFP_ZERO not used)
+	* or user folios require special handling, folio_zero_user() is used to
+	* make sure that the page corresponding to the faulting address will be
+	* hot in the cache after zeroing.
 	*/
-	if (!alloc_zeroed())
+	if (alloc_need_zeroing())
 		folio_zero_user(folio, addr);
 	/*
 	 * The memory barrier inside __folio_mark_uptodate makes sure that
diff --git a/mm/internal.h b/mm/internal.h
index cb8d8e8e3ffa..3bd08bafad04 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1285,12 +1285,6 @@ void touch_pud(struct vm_area_struct *vma, unsigned long addr,
 void touch_pmd(struct vm_area_struct *vma, unsigned long addr,
 	       pmd_t *pmd, bool write);
 
-static inline bool alloc_zeroed(void)
-{
-	return static_branch_maybe(CONFIG_INIT_ON_ALLOC_DEFAULT_ON,
-			&init_on_alloc);
-}
-
 /*
  * Parses a string with mem suffixes into its order. Useful to parse kernel
  * parameters.
diff --git a/mm/memory.c b/mm/memory.c
index 75c2dfd04f72..cf1611791856 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4733,12 +4733,12 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 			folio_throttle_swaprate(folio, gfp);
 			/*
 			 * When a folio is not zeroed during allocation
-			 * (__GFP_ZERO not used), folio_zero_user() is used
-			 * to make sure that the page corresponding to the
-			 * faulting address will be hot in the cache after
-			 * zeroing.
+			 * (__GFP_ZERO not used) or user folios require special
+			 * handling, folio_zero_user() is used to make sure
+			 * that the page corresponding to the faulting address
+			 * will be hot in the cache after zeroing.
 			 */
-			if (!alloc_zeroed())
+			if (alloc_need_zeroing())
 				folio_zero_user(folio, vmf->address);
 			return folio;
 		}
-- 
2.45.2

Re: [PATCH] mm: use clear_user_(high)page() for arch with special user folio handling

[Matthew Wilcox]

On Fri, Dec 06, 2024 at 09:19:38AM -0500, Zi Yan wrote:
> For architectures setting ARCH_HAS_CPU_CACHE_ALIASING, which requires
> flushing cache and arc, which sets folio->flags after clearing a user
> folio

I think arc just has some legacy code left that needs to be ripped out.
See commit d5272aaa8257 which took away ARCH_HAS_CPU_CACHE_ALIASING
from arc.

Looking at 8690bbcf3b70, I wonder if you want to use
cpu_dcache_is_aliasing() here?

Re: [PATCH] mm: use clear_user_(high)page() for arch with special user folio handling

[Zi Yan]

On 6 Dec 2024, at 11:42, Matthew Wilcox wrote:

> On Fri, Dec 06, 2024 at 09:19:38AM -0500, Zi Yan wrote:
>> For architectures setting ARCH_HAS_CPU_CACHE_ALIASING, which requires
>> flushing cache and arc, which sets folio->flags after clearing a user
>> folio
>
> I think arc just has some legacy code left that needs to be ripped out.
> See commit d5272aaa8257 which took away ARCH_HAS_CPU_CACHE_ALIASING
> from arc.

The PG_dc_clean bit seems not to be related to cache aliasing.
See commit eacd0e950dc2 ("ARC: [mm] Lazy D-cache flush (non aliasing VIPT)")

>
> Looking at 8690bbcf3b70, I wonder if you want to use
> cpu_dcache_is_aliasing() here?

Yeah, this is more precise. Will use this in my next version. Thanks.

Best Regards,
Yan, Zi

Re: [PATCH] mm: use clear_user_(high)page() for arch with special user folio handling

[Vineet Gupta]

On 12/6/24 09:08, Zi Yan wrote:
> On 6 Dec 2024, at 11:42, Matthew Wilcox wrote:
>
>> On Fri, Dec 06, 2024 at 09:19:38AM -0500, Zi Yan wrote:
>>> For architectures setting ARCH_HAS_CPU_CACHE_ALIASING, which requires
>>> flushing cache and arc, which sets folio->flags after clearing a user
>>> folio
>> I think arc just has some legacy code left that needs to be ripped out.
>> See commit d5272aaa8257 which took away ARCH_HAS_CPU_CACHE_ALIASING
>> from arc.
> The PG_dc_clean bit seems not to be related to cache aliasing.
> See commit eacd0e950dc2 ("ARC: [mm] Lazy D-cache flush (non aliasing VIPT)")

Indeed it is not related to aliasing.

>> Looking at 8690bbcf3b70, I wonder if you want to use
>> cpu_dcache_is_aliasing() here?
> Yeah, this is more precise. Will use this in my next version. Thanks.

Commit 8690bbcf3b70 was wrong for ARC as it assumed aliasing is true. The
aliasing D$ code is all gone and cpu_dcache_is_aliasing() is false for ARC now.

-vineet