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Message-ID: <acd263a4-824c-4c8d-a3e2-8b2f391fc775@efficios.com>
Date: Sat, 7 Dec 2024 10:31:44 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Vlastimil Babka <vbabka@...e.cz>, David Hildenbrand <david@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Miaohe Lin <linmiaohe@...wei.com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
John Hubbard <jhubbard@...dia.com>,
"Huang, Ying" <ying.huang@...ux.alibaba.com>,
Ryan Roberts <ryan.roberts@....com>, Alexander Potapenko
<glider@...gle.com>, Kees Cook <keescook@...omium.org>,
Vineet Gupta <vgupta@...nel.org>, linux-kernel@...r.kernel.org,
Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v2] mm: use clear_user_(high)page() for arch with special
user folio handling
On 2024-12-06 12:42, Zi Yan wrote:
> For architectures setting cpu_dcache_is_aliasing() to true, which require
> flushing cache, and arc, which changes folio->flags after clearing a user
> folio, __GFP_ZERO using 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() when
> cpu_dcache_is_aliasing() is true or architecture is 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@...der.be>
> Closes: https://lore.kernel.org/linux-mm/CAMuHMdV1hRp_NtR5YnJo=HsfgKQeH91J537Gh4gKk3PFZhSkbA@mail.gmail.com/
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Zi Yan <ziy@...dia.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..ca8df5871213 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -31,6 +31,7 @@
> #include <linux/kasan.h>
> #include <linux/memremap.h>
> #include <linux/slab.h>
> +#include <linux/cacheinfo.h>
>
> struct mempolicy;
> struct anon_vma;
> @@ -4175,6 +4176,22 @@ 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 changes folio->flags, so always return false to make caller use
> + * clear_user_page()/clear_user_highpage()
> + */
> + return (cpu_dcache_is_aliasing() || IS_ENABLED(CONFIG_ARC)) ||
Nack.
Can we please not go back to re-introducing arch-specific
conditionals in generic mm code after the cleanup I did when
introducing cpu_dcache_is_aliasing() in commit 8690bbcf3b70 ?
Based on commit eacd0e950dc2, AFAIU what you appear to need here
is to introduce a:
cpu_icache_is_aliasing() -> note the "i" for instruction cache
It would typically be directly set to
#define cpu_icache_is_aliasing() cpu_dcache_is_aliasing()
except on architecture like ARC when the icache vs dcache
is aliasing, but not dcache vs dcache.
So for ARC it would be defined as:
#define cpu_dcache_is_aliasing() false
#define cpu_icache_is_aliasing() true
And the Kconfig ARCH_HAS_CPU_CACHE_ALIASING=y would be set for ARC
again.
I'm not entirely sure if we want to go for the wording "is_aliasing"
or "is_incoherent" when talking about icache vs dcache, so I'm open
to ideas here.
Thanks,
Mathieu
> + !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;
> }
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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