linux-kernel - Re: [PATCH] arm64: mm: Make flush_tlb_fix_spurious

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Date:   Wed, 30 Sep 2020 18:14:04 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH] arm64: mm: Make flush_tlb_fix_spurious_fault() a no-op

On Wed, Sep 30, 2020 at 02:18:59PM +0100, Will Deacon wrote:
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index f07333e86c2f..a696a7921da4 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -218,7 +218,9 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
>  		pteval = cmpxchg_relaxed(&pte_val(*ptep), old_pteval, pteval);
>  	} while (pteval != old_pteval);
>  
> -	flush_tlb_fix_spurious_fault(vma, address);
> +	/* Invalidate a stale read-only entry */
> +	if (dirty)
> +		flush_tlb_page(vma, address);
>  	return 1;

In my proposal I had a pte_accessible(pte) check instead of dirty here
since we may go for an old pte directly to a writable one and a TLBI
wouldn't be needed. Not that it matters from a performance perspective.

Either way,

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