linux-kernel - Re: [PATCH] MIPS: update tlb even if pte entry has no change

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Date:   Thu, 14 May 2020 12:33:59 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Bibo Mao <maobibo@...ngson.cn>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Burton <paulburton@...nel.org>,
        Dmitry Korotin <dkorotin@...ecomp.com>,
        Philippe Mathieu-Daudé <f4bug@...at.org>,
        Stafford Horne <shorne@...il.com>,
        Steven Price <steven.price@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] MIPS: update tlb even if pte entry has no change

On Thu, May 14, 2020 at 10:17:57AM +0800, Bibo Mao wrote:
> From: bibo mao <maobibo@...ngson.cn>
> 
> If there are two threads reading the same memory and tlb miss happens,
> one thread fills pte entry, the other reads new pte value during page fault
> handling. PTE value may be updated before page faul, so the process need
> need update tlb still.
> 
> Also this patch define flush_tlb_fix_spurious_fault as empty, since it not
> necessary to flush the page for all CPUs

I'm not familiar enough with MIPS TLB workings, but it seems that adding
a MIPS version of ptep_set_access_flags() and relaxing
flush_tlb_fix_spurious_fault() are two separate patches.

> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>  arch/mips/include/asm/pgtable.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
> index aab0ec1..d0a4940 100644
> --- a/arch/mips/include/asm/pgtable.h
> +++ b/arch/mips/include/asm/pgtable.h
> @@ -635,6 +635,26 @@ static inline pmd_t pmd_mknotpresent(pmd_t pmd)
>  	return pmd;
>  }
>  
> +#define flush_tlb_fix_spurious_fault(vma, address) do { } while (0)
> +
> +#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
> +int ptep_set_access_flags(struct vm_area_struct *vma,
> +			unsigned long address, pte_t *ptep,
> +			pte_t entry, int dirty)
> +{
> +	int changed = !pte_same(*ptep, entry);
> +
> +	if (changed)
> +		set_pte_at(vma->vm_mm, address, ptep, entry);
> +	else
> +		/* update tlb with latest pte entry still, tlb entry is old
> +		 * since there is page fault
> +		 */
> +		update_mmu_cache(vma, address, ptep);
> +
> +	return changed;
> +}
> +
>  /*
>   * The generic version pmdp_huge_get_and_clear uses a version of pmd_clear() with a
>   * different prototype.
> -- 
> 1.8.3.1
> 

-- 
Sincerely yours,
Mike.