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From: Yu Zhao <yuzhao@google.com>
To: Will Deacon <will@kernel.org>
Cc: kernel-team@android.com,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Minchan Kim <minchan@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 6/6] mm: proc: Avoid fullmm flush for young/dirty bit toggling
Date: Fri, 20 Nov 2020 13:40:05 -0700	[thread overview]
Message-ID: <20201120204005.GC1303870@google.com> (raw)
In-Reply-To: <20201120143557.6715-7-will@kernel.org>

On Fri, Nov 20, 2020 at 02:35:57PM +0000, Will Deacon wrote:
> clear_refs_write() uses the 'fullmm' API for invalidating TLBs after
> updating the page-tables for the current mm. However, since the mm is not
> being freed, this can result in stale TLB entries on architectures which
> elide 'fullmm' invalidation.
> 
> Ensure that TLB invalidation is performed after updating soft-dirty
> entries via clear_refs_write() by using the non-fullmm API to MMU gather.
> 
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  fs/proc/task_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index a76d339b5754..316af047f1aa 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1238,7 +1238,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
>  			count = -EINTR;
>  			goto out_mm;
>  		}
> -		tlb_gather_mmu_fullmm(&tlb, mm);
> +		tlb_gather_mmu(&tlb, mm, 0, TASK_SIZE);

Let's assume my reply to patch 4 is wrong, and therefore we still need
tlb_gather/finish_mmu() here. But then wouldn't this change deprive
architectures other than ARM the opportunity to optimize based on the
fact it's a full-mm flush?

It seems to me ARM's interpretation of tlb->fullmm is a special case,
not the other way around.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Yu Zhao <yuzhao@google.com>
To: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org, kernel-team@android.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	Minchan Kim <minchan@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 6/6] mm: proc: Avoid fullmm flush for young/dirty bit toggling
Date: Fri, 20 Nov 2020 13:40:05 -0700	[thread overview]
Message-ID: <20201120204005.GC1303870@google.com> (raw)
In-Reply-To: <20201120143557.6715-7-will@kernel.org>

On Fri, Nov 20, 2020 at 02:35:57PM +0000, Will Deacon wrote:
> clear_refs_write() uses the 'fullmm' API for invalidating TLBs after
> updating the page-tables for the current mm. However, since the mm is not
> being freed, this can result in stale TLB entries on architectures which
> elide 'fullmm' invalidation.
> 
> Ensure that TLB invalidation is performed after updating soft-dirty
> entries via clear_refs_write() by using the non-fullmm API to MMU gather.
> 
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  fs/proc/task_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index a76d339b5754..316af047f1aa 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1238,7 +1238,7 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf,
>  			count = -EINTR;
>  			goto out_mm;
>  		}
> -		tlb_gather_mmu_fullmm(&tlb, mm);
> +		tlb_gather_mmu(&tlb, mm, 0, TASK_SIZE);

Let's assume my reply to patch 4 is wrong, and therefore we still need
tlb_gather/finish_mmu() here. But then wouldn't this change deprive
architectures other than ARM the opportunity to optimize based on the
fact it's a full-mm flush?

It seems to me ARM's interpretation of tlb->fullmm is a special case,
not the other way around.


  parent reply	other threads:[~2020-11-20 20:40 UTC|newest]

Thread overview: 85+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-20 14:35 [PATCH 0/6] tlb: Fix access and (soft-)dirty bit management Will Deacon
2020-11-20 14:35 ` Will Deacon
2020-11-20 14:35 ` [PATCH 1/6] arm64: pgtable: Fix pte_accessible() Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 16:03   ` Minchan Kim
2020-11-20 16:03     ` Minchan Kim
2020-11-20 19:53   ` Yu Zhao
2020-11-20 19:53     ` Yu Zhao
2020-11-23 13:27   ` Catalin Marinas
2020-11-23 13:27     ` Catalin Marinas
2020-11-24 10:02   ` Anshuman Khandual
2020-11-24 10:02     ` Anshuman Khandual
2020-11-20 14:35 ` [PATCH 2/6] arm64: pgtable: Ensure dirty bit is preserved across pte_wrprotect() Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 17:09   ` Minchan Kim
2020-11-20 17:09     ` Minchan Kim
2020-11-23 14:31     ` Catalin Marinas
2020-11-23 14:31       ` Catalin Marinas
2020-11-23 14:22   ` Catalin Marinas
2020-11-23 14:22     ` Catalin Marinas
2020-11-20 14:35 ` [PATCH 3/6] tlb: mmu_gather: Remove unused start/end arguments from tlb_finish_mmu() Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 17:20   ` Linus Torvalds
2020-11-20 17:20     ` Linus Torvalds
2020-11-23 16:48     ` Will Deacon
2020-11-23 16:48       ` Will Deacon
2020-11-20 14:35 ` [PATCH 4/6] mm: proc: Invalidate TLB after clearing soft-dirty page state Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 15:00   ` Peter Zijlstra
2020-11-20 15:00     ` Peter Zijlstra
2020-11-20 15:09     ` Peter Zijlstra
2020-11-20 15:09       ` Peter Zijlstra
2020-11-20 15:15     ` Will Deacon
2020-11-20 15:15       ` Will Deacon
2020-11-20 15:27       ` Peter Zijlstra
2020-11-20 15:27         ` Peter Zijlstra
2020-11-23 18:23         ` Will Deacon
2020-11-23 18:23           ` Will Deacon
2020-11-20 15:55     ` Minchan Kim
2020-11-20 15:55       ` Minchan Kim
2020-11-23 18:41       ` Will Deacon
2020-11-23 18:41         ` Will Deacon
2020-11-25 22:51         ` Minchan Kim
2020-11-25 22:51           ` Minchan Kim
2020-11-20 20:22   ` Yu Zhao
2020-11-20 20:22     ` Yu Zhao
2020-11-21  2:49     ` Yu Zhao
2020-11-21  2:49       ` Yu Zhao
2020-11-23 19:21       ` Yu Zhao
2020-11-23 19:21         ` Yu Zhao
2020-11-23 22:04       ` Will Deacon
2020-11-23 22:04         ` Will Deacon
2020-11-20 14:35 ` [PATCH 5/6] tlb: mmu_gather: Introduce tlb_gather_mmu_fullmm() Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 17:22   ` Linus Torvalds
2020-11-20 17:22     ` Linus Torvalds
2020-11-20 17:31     ` Linus Torvalds
2020-11-20 17:31       ` Linus Torvalds
2020-11-23 16:48       ` Will Deacon
2020-11-23 16:48         ` Will Deacon
2020-11-22 15:11   ` [tlb] e242a269fa: WARNING:at_mm/mmu_gather.c:#tlb_gather_mmu kernel test robot
2020-11-23 17:51     ` Will Deacon
2020-11-23 17:51       ` Will Deacon
2020-11-20 14:35 ` [PATCH 6/6] mm: proc: Avoid fullmm flush for young/dirty bit toggling Will Deacon
2020-11-20 14:35   ` Will Deacon
2020-11-20 17:41   ` Linus Torvalds
2020-11-20 17:41     ` Linus Torvalds
2020-11-20 17:45     ` Linus Torvalds
2020-11-20 17:45       ` Linus Torvalds
2020-11-20 20:40   ` Yu Zhao [this message]
2020-11-20 20:40     ` Yu Zhao
2020-11-23 18:35     ` Will Deacon
2020-11-23 18:35       ` Will Deacon
2020-11-23 20:04       ` Yu Zhao
2020-11-23 20:04         ` Yu Zhao
2020-11-23 21:17         ` Will Deacon
2020-11-23 21:17           ` Will Deacon
2020-11-24  1:13           ` Yu Zhao
2020-11-24  1:13             ` Yu Zhao
2020-11-24 14:31             ` Will Deacon
2020-11-24 14:31               ` Will Deacon
2020-11-25 22:01             ` Minchan Kim
2020-11-25 22:01               ` Minchan Kim
2020-11-24 14:46     ` Peter Zijlstra
2020-11-24 14:46       ` Peter Zijlstra

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