+Vlastimil
On 11 Oct 2024, at 11:03, Zi Yan wrote:
> Commit 6471384af2a6 ("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.
>
> Added alloc_zeroed() helper to encapsulate the init_on_alloc check.
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> include/linux/highmem.h | 8 +-------
> mm/huge_memory.c | 3 ++-
> mm/internal.h | 6 ++++++
> mm/memory.c | 3 ++-
> 4 files changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index bec9bd715acf..6e452bd8e7e3 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -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
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 82f464865570..5dcbea96edb7 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1176,7 +1176,8 @@ static struct folio *vma_alloc_anon_folio_pmd(struct vm_area_struct *vma,
> }
> folio_throttle_swaprate(folio, gfp);
>
> - folio_zero_user(folio, addr);
> + if (!alloc_zeroed())
> + folio_zero_user(folio, addr);
> /*
> * The memory barrier inside __folio_mark_uptodate makes sure that
> * folio_zero_user writes become visible before the set_pmd_at()
> diff --git a/mm/internal.h b/mm/internal.h
> index 906da6280c2d..508f7802dd2b 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -1233,6 +1233,12 @@ 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,
> diff --git a/mm/memory.c b/mm/memory.c
> index c67359ddb61a..88252f0e06d0 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4719,7 +4719,8 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
> goto next;
> }
> folio_throttle_swaprate(folio, gfp);
> - folio_zero_user(folio, vmf->address);
> + if (!alloc_zeroed())
> + folio_zero_user(folio, vmf->address);
> return folio;
> }
> next:
> --
> 2.45.2
Best Regards,
Yan, Zi
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