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

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Message-ID: <1abd8a86-6e04-b69b-6f25-c3ff8201ea5d@loongson.cn>
Date:   Thu, 14 May 2020 19:40:20 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     Mike Rapoport <rppt@...ux.ibm.com>
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 05/14/2020 05:33 PM, Mike Rapoport wrote:
> 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.

Well, will split it into two patches.


regards
bibo, mao
> 
>> 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
>>
>