Commit 5708d96d authored by Zi Yan's avatar Zi Yan Committed by Andrew Morton
Browse files

mm: avoid zeroing user movable page twice with init_on_alloc=1 

Commit 6471384a ("mm: security: introduce init_on_alloc=1 and
init_on_free=1 boot options") forces allocated page to be zeroed in
post_alloc_hook() when init_on_alloc=1.

For order-0 folios, if arch does not define
vma_alloc_zeroed_movable_folio(), the default implementation again zeros
the page return from the buddy allocator.  So the page is zeroed twice. 
Fix it by passing __GFP_ZERO instead to avoid double page zeroing.  At the
moment, s390,arm64,x86,alpha,m68k are not impacted since they define their
own vma_alloc_zeroed_movable_folio().

For >0 order folios (mTHP and PMD THP), folio_zero_user() is called to
zero the folio again.  Fix it by calling folio_zero_user() only if
init_on_alloc is set.  All arch are impacted.

Add alloc_zeroed() helper to encapsulate the init_on_alloc check.

[ziy@nvidia.com: comment fixes, per David]
  Link: https://lkml.kernel.org/r/97DB52E1-C594-49B5-9736-89AC302FAB01@nvidia.com
Link: https://lkml.kernel.org/r/20241011150304.709590-1-ziy@nvidia.com


Signed-off-by: default avatarZi Yan <ziy@nvidia.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 773ee2cd

include/linux/highmem.h

+1 −7
Original line number Diff line number Diff line
@@ -224,13 +224,7 @@ static inline 
struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,

				   unsigned long vaddr)

{

	struct folio *folio;



	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);

	if (folio)

		clear_user_highpage(&folio->page, vaddr);



	return folio;

	return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr);

}

#endif

mm/huge_memory.c

+7 −1
Original line number Diff line number Diff line
@@ -1162,6 +1162,12 @@ 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.

	*/

	if (!alloc_zeroed())

		folio_zero_user(folio, addr);

	/*

	 * The memory barrier inside __folio_mark_uptodate makes sure that

mm/internal.h

+6 −0
Original line number Diff line number Diff line
@@ -1276,6 +1276,12 @@ 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);

}



enum {

	/* mark page accessed */

	FOLL_TOUCH = 1 << 16,

mm/memory.c

+9 −1
Original line number Diff line number Diff line
@@ -4719,6 +4719,14 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) 
				goto next;

			}

			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.

			 */

			if (!alloc_zeroed())

				folio_zero_user(folio, vmf->address);

			return folio;

		}