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Date:   Mon, 23 Nov 2020 13:27:52 +0000
From:   Catalin Marinas <>
To:     Will Deacon <>
        Yu Zhao <>, Minchan Kim <>,
        Peter Zijlstra <>,
        Linus Torvalds <>,
        Anshuman Khandual <>,,,
Subject: Re: [PATCH 1/6] arm64: pgtable: Fix pte_accessible()

On Fri, Nov 20, 2020 at 02:35:52PM +0000, Will Deacon wrote:
> pte_accessible() is used by ptep_clear_flush() to figure out whether TLB
> invalidation is necessary when unmapping pages for reclaim. Although our
> implementation is correct according to the architecture, returning true
> only for valid, young ptes in the absence of racing page-table
> modifications, this is in fact flawed due to lazy invalidation of old
> ptes in ptep_clear_flush_young() where we elide the expensive DSB
> instruction for completing the TLB invalidation.
> Rather than penalise the aging path, adjust pte_accessible() to return
> true for any valid pte, even if the access flag is cleared.
> Cc: <>
> Fixes: 76c714be0e5e ("arm64: pgtable: implement pte_accessible()")
> Reported-by: Yu Zhao <>
> Signed-off-by: Will Deacon <>

Reviewed-by: Catalin Marinas <>

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