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Date:   Wed, 24 May 2023 21:26:46 +0800
From:   Jisheng Zhang <jszhang@kernel.org>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: mm: pass original fault address to
 handle_mm_fault() in PER_VMA_LOCK block
Message-ID: <ZG4QlvkkaoBlyoFC@xhacker>
References: <20230524131238.2791-1-jszhang@kernel.org>
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In-Reply-To: <20230524131238.2791-1-jszhang@kernel.org>
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On Wed, May 24, 2023 at 09:12:38PM +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:

OOPS, sorry please ignore this one. I pressed ctrl-c to interrupt the
git send-mail, but it's still sent out ;)

Instead, let's focus on
https://lore.kernel.org/linux-arm-kernel/20230524131305.2808-1-jszhang@kernel.org/T/#u

The two patches are the same, I just added Suren into CC list.

> 
> 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@kernel.org>
> ---
>  arch/arm64/mm/fault.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index cb21ccd7940d..6045a5117ac1 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -600,8 +600,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr,
>  		vma_end_read(vma);
>  		goto lock_mmap;
>  	}
> -	fault = handle_mm_fault(vma, addr & PAGE_MASK,
> -				mm_flags | FAULT_FLAG_VMA_LOCK, regs);
> +	fault = handle_mm_fault(vma, addr, mm_flags | FAULT_FLAG_VMA_LOCK, regs);
>  	vma_end_read(vma);
>  
>  	if (!(fault & VM_FAULT_RETRY)) {
> -- 
> 2.40.1
> 
> 
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