linux-kernel - Re: [RFC PATCH 2/2] mm: mmu_notifier fix for tlb_end

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Message-ID: <20180823134104.GD1496@brain-police>
Date:   Thu, 23 Aug 2018 14:41:05 +0100
From:   Will Deacon <will.deacon@....com>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        torvalds@...ux-foundation.org, luto@...nel.org, x86@...nel.org,
        bp@...en8.de, riel@...riel.com, jannh@...gle.com,
        ascannell@...gle.com, dave.hansen@...el.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        David Miller <davem@...emloft.net>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] mm: mmu_notifier fix for tlb_end_vma

On Thu, Aug 23, 2018 at 06:47:09PM +1000, Nicholas Piggin wrote:
> The generic tlb_end_vma does not call invalidate_range mmu notifier,
> and it resets resets the mmu_gather range, which means the notifier
> won't be called on part of the range in case of an unmap that spans
> multiple vmas.
> 
> ARM64 seems to be the only arch I could see that has notifiers and
> uses the generic tlb_end_vma. I have not actually tested it.
> 
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
>  include/asm-generic/tlb.h | 17 +++++++++++++----
>  mm/memory.c               | 10 ----------
>  2 files changed, 13 insertions(+), 14 deletions(-)

I think we only use the notifiers in the KVM code, which appears to leave
the ->invalidate_range() callback empty, so that at least explains why we
haven't run into problems here.

But the change looks correct to me, so:

Acked-by: Will Deacon <will.deacon@....com>

Thanks,

Will