Re: [PATCH v2 1/3] powerpc/mm: Export flush_all_mm()

[Frederic Barrat <fbarrat@linux.vnet.ibm.com>]

Le 30/08/2017 à 15:17, Michael Ellerman a écrit :
> Frederic Barrat <fbarrat@linux.vnet.ibm.com> writes:
> 
>> With the optimizations introduced by commit a46cc7a90fd8
>> ("powerpc/mm/radix: Improve TLB/PWC flushes"), flush_tlb_mm() no
>> longer flushes the page walk cache with radix. This patch introduces
>> flush_all_mm(), which flushes everything, tlb and pwc, for a given mm.
>>
>> Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
>> ---
>> Changelog:
>> v2: this patch is new
>>
>>   arch/powerpc/include/asm/book3s/64/tlbflush-hash.h  |  8 ++++++++
>>   arch/powerpc/include/asm/book3s/64/tlbflush-radix.h |  3 +++
>>   arch/powerpc/include/asm/book3s/64/tlbflush.h       | 15 +++++++++++++++
>>   arch/powerpc/mm/tlb-radix.c                         |  6 ++++--
>>   4 files changed, 30 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> index 2f6373144e2c..c5d89d271a96 100644
>> --- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
>> @@ -65,6 +65,14 @@ static inline void hash__flush_tlb_mm(struct mm_struct *mm)
>>   {
>>   }
>>   
>> +static inline void hash__local_flush_all_mm(struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void hash__flush_all_mm(struct mm_struct *mm)
>> +{
>> +}
> 
> It's not clear why it makes sense for these to be empty. Either for the
> general idea of the "flush_all_mm()" API, or for your intended use by
> CXL.

I was not too sure what to do for hash, but the idea is that the new 
flush_all_mm() is really the equivalent of the old flush_tlb_mm() from 
before Ben's optimizations for radix, and that was/still is an empty 
operation on hash, so I kept it that way.

We don't support hash for capi2 yet. Adding it will definitely require 
some work in that area, as the current approach (use count on the driver 
and all TLBIs becoming global when the driver is in use) won't hold much 
longer.

   Fred