Re: [Xen-devel] [PATCHv1] CA-201372: x86: don't flush the whole cache when changing cachability

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 09/03/16 14:01, Jan Beulich wrote:
>>>> On 08.03.16 at 19:44, <david.vrabel@xxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/flushtlb.c
>> +++ b/xen/arch/x86/flushtlb.c
>> @@ -140,7 +140,8 @@ unsigned int flush_area_local(const void *va, unsigned 
>> int flags)
>>          if ( order < (BITS_PER_LONG - PAGE_SHIFT) )
>>              sz = 1UL << (order + PAGE_SHIFT);
>>  
>> -        if ( !(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) &&
>> +        if ( (!(flags & (FLUSH_TLB|FLUSH_TLB_GLOBAL)) ||
>> +              flags & FLUSH_VA_VALID) &&
> 
> The & wants to be parenthesized.

Style nit-picks really should come with a patch to CODING_STYLE.  The
existing code isn't consistent enough to deduce the preferred style.

>> --- a/xen/arch/x86/mm.c
>> +++ b/xen/arch/x86/mm.c
>> @@ -5641,7 +5641,7 @@ int map_pages_to_xen(
>>          flush_flags |= FLUSH_TLB_GLOBAL;       \
>>      if ( (flags & _PAGE_PRESENT) &&            \
>>           (((o_) ^ flags) & PAGE_CACHE_ATTRS) ) \
>> -        flush_flags |= FLUSH_CACHE;            \
>> +        flush_flags |= FLUSH_CACHE_BY_VA;      \
>>  } while (0)
> 
> No, that's too simple. You may flush by VA only if the MFN didn't
> change (or else you flush the wrong page).

Cachability changes goes through update_xen_mappings() which always uses
the same MFN -> virt mapping so the MFN never changes.

David

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