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

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Message-ID: <0b136cc3-c85e-1183-5ddc-ab99fd58c012@arm.com>
Date:   Thu, 25 May 2023 12:30:04 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Jisheng Zhang <jszhang@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: mm: pass original fault address to
 handle_mm_fault() in PER_VMA_LOCK block



On 5/24/23 18:42, 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>

LGTM

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>

> ---
>  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)) {