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Message-ID: <CAMuHMdXbugTBrK5yqRB6ysHcEq8POCu3O37BUPU4i-8rLsQY2g@mail.gmail.com>
Date: Fri, 6 Dec 2024 09:37:12 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Zi Yan <ziy@...dia.com>
Cc: Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>,
Miaohe Lin <linmiaohe@...wei.com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
John Hubbard <jhubbard@...dia.com>, "Huang, Ying" <ying.huang@...el.com>,
Ryan Roberts <ryan.roberts@....com>, Alexander Potapenko <glider@...gle.com>,
Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
linux-mips@...r.kernel.org
Subject: Re: [PATCH] mm: avoid zeroing user movable page twice with init_on_alloc=1
Hi Zi,
On Thu, Dec 5, 2024 at 6:33 PM Zi Yan <ziy@...dia.com> wrote:
> Can you try the patch below (it compiles locally for mips and x86) to see
> if your issue is fixed? Can you please make THP always on in your config,
> since THP is also affected by the same issue? The patch you tested only
> fixed non THP config.
Thanks, this works both without THP, and with
CONFIG_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Thanks. I appreciate your help. :)
Thanks, I appreciate your quick responses and solutions!
> --- 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;
> }
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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