linux-kernel - Re: [PATCH] arm64: mm: pass original fault address to handle_mm_fault() in PER_VMA

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Message-ID: <ZG+U/70SxgfaM6sl@arm.com>
Date:   Thu, 25 May 2023 18:03:59 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Jisheng Zhang <jszhang@...nel.org>
Cc:     Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH] arm64: mm: pass original fault address to
 handle_mm_fault() in PER_VMA_LOCK block

On Wed, May 24, 2023 at 09:13:05PM +0800, Jisheng Zhang wrote:
> When reading the arm64's PER_VMA_LOCK support code, I found a bit
> difference between arm64 and other arch when calling handle_mm_fault()
> during VMA lock-based page fault handling: the fault address is masked
> before passing to handle_mm_fault(). This is also different from the
> usage in mmap_lock-based handling. I think we need to pass the
> original fault address to handle_mm_fault() as we did in
> commit 84c5e23edecd ("arm64: mm: Pass original fault address to
> handle_mm_fault()").
> 
> If we go through the code path further, we can find that the "masked"
> fault address can cause mismatched fault address between perf sw
> major/minor page fault sw event and perf page fault sw event:
> 
> do_page_fault
>   perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, ..., addr)   // orig addr
>   handle_mm_fault
>     mm_account_fault
>       perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, ...) // masked addr
> 
> Fixes: cd7f176aea5f ("arm64/mm: try VMA lock-based page fault handling first")
> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>

Acked-by: Catalin Marinas <catalin.marinas@....com>