From: Linus Torvalds <torvalds@linux-foundation.org>
To: Will Deacon <will@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Android Kernel Team <kernel-team@android.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Yu Zhao <yuzhao@google.com>, Minchan Kim <minchan@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Linux-MM <linux-mm@kvack.org>,
Linux ARM <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 09:41:54 -0800 [thread overview]
Message-ID: <CAHk-=wjKjnT=yNnRgfPRknOBYF4oJHixbT10wDqXpjQ1qiW7SA@mail.gmail.com> (raw)
In-Reply-To: <20201120143557.6715-7-will@kernel.org>
On Fri, Nov 20, 2020 at 6:36 AM Will Deacon <will@kernel.org> wrote:
>
> Ensure that TLB invalidation is performed after updating soft-dirty
> entries via clear_refs_write() by using the non-fullmm API to MMU gather.
This code sequence looks bogus to begin with.
It does that
tlb_gather_mmu(&tlb, mm, 0, -1);
..
tlb_finish_mmu(&tlb, 0, -1);
around the loop (all, your patch series changes those arguments), but
it doesn't actually use "tlb" anywhere inside the loop itself that I
can see.
Yeah., yeah, it sets the flush_pending thing etc, but that still
sounds fundamentally wrong. It should do the proper range adjustments
if/when it actually wals the range. No?
If I read this all right, it will do a full TLB flush even when it
doesn't do anything (eg CLEAR_REFS_SOFT_DIRTY with no softdirty
pages).
So this looks all kinds of bogus. Not your patch, but the code it patches.
Linus
WARNING: multiple messages have this Message-ID (diff)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Minchan Kim <minchan@kernel.org>,
Android Kernel Team <kernel-team@android.com>,
Linux ARM <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 09:41:54 -0800 [thread overview]
Message-ID: <CAHk-=wjKjnT=yNnRgfPRknOBYF4oJHixbT10wDqXpjQ1qiW7SA@mail.gmail.com> (raw)
In-Reply-To: <20201120143557.6715-7-will@kernel.org>
On Fri, Nov 20, 2020 at 6:36 AM Will Deacon <will@kernel.org> wrote:
>
> Ensure that TLB invalidation is performed after updating soft-dirty
> entries via clear_refs_write() by using the non-fullmm API to MMU gather.
This code sequence looks bogus to begin with.
It does that
tlb_gather_mmu(&tlb, mm, 0, -1);
..
tlb_finish_mmu(&tlb, 0, -1);
around the loop (all, your patch series changes those arguments), but
it doesn't actually use "tlb" anywhere inside the loop itself that I
can see.
Yeah., yeah, it sets the flush_pending thing etc, but that still
sounds fundamentally wrong. It should do the proper range adjustments
if/when it actually wals the range. No?
If I read this all right, it will do a full TLB flush even when it
doesn't do anything (eg CLEAR_REFS_SOFT_DIRTY with no softdirty
pages).
So this looks all kinds of bogus. Not your patch, but the code it patches.
Linus
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next prev parent reply other threads:[~2020-11-20 17:42 UTC|newest]
Thread overview: 91+ 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
2020-11-20 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 17:22 ` Linus Torvalds
2020-11-20 17:31 ` 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
2021-02-01 11:32 ` [tip: core/mm] tlb: mmu_gather: Remove start/end arguments from tlb_gather_mmu() tip-bot2 for 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 [this message]
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 17:45 ` Linus Torvalds
2020-11-20 20:40 ` Yu Zhao
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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