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Subject: Re: [PATCH v4 6/9] mm/mremap: Use range flush that does TLB and page
 walk cache flush
To: Michael Ellerman <mpe@ellerman.id.au>, linux-mm@kvack.org,
 akpm@linux-foundation.org
References: <20210414085915.301189-1-aneesh.kumar@linux.ibm.com>
 <20210414085915.301189-7-aneesh.kumar@linux.ibm.com>
 <87fszld3bt.fsf@mpe.ellerman.id.au>
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Message-ID: <18072419-dcf8-ef12-380f-50a55be41ccb@linux.ibm.com>
Date: Tue, 20 Apr 2021 09:47:52 +0530
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On 4/20/21 9:17 AM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
>> Some architectures do have the concept of page walk cache which need
>> to be flush when updating higher levels of page tables. A fast mremap
>> that involves moving page table pages instead of copying pte entries
>> should flush page walk cache since the old translation cache is no more
>> valid.
>>
>> Add new helper flush_pte_tlb_pwc_range() which invalidates both TLB and
>> page walk cache where TLB entries are mapped with page size PAGE_SIZE.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>   arch/powerpc/include/asm/book3s/64/tlbflush.h | 11 +++++++++++
>>   mm/mremap.c                                   | 15 +++++++++++++--
>>   2 files changed, 24 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush.h b/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> index f9f8a3a264f7..c236b66f490b 100644
>> --- a/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush.h
>> @@ -80,6 +80,17 @@ static inline void flush_hugetlb_tlb_range(struct vm_area_struct *vma,
>>   	return flush_hugetlb_tlb_pwc_range(vma, start, end, false);
>>   }
>>   
>> +#define flush_pte_tlb_pwc_range flush_tlb_pwc_range
>> +static inline void flush_pte_tlb_pwc_range(struct vm_area_struct *vma,
>> +					   unsigned long start, unsigned long end,
>> +					   bool also_pwc)
> 
> This still uses the also_pwc name, which is a bit inconsistent with the
> previous patch.
> 

will fix that.

> But, does it even need to be a parameter? AFAICS you always pass true,
> and pwc=true is sort of implied by the name isn't it?
> 

I don't have strong opinion about that. I was wondering having flush_pwc 
explicitly called out is a better indication of we are flushing page 
walk cache. Will drop that in the next update.


-aneesh