Re: [Xen-devel] [PATCH 2/2] x86: use invpcid to do global flushing

[Juergen Gross <jgross@xxxxxxxx>]

On 09/03/18 16:29, Jan Beulich wrote:
>>>> On 05.03.18 at 10:50, <wei.liu2@xxxxxxxxxx> wrote:
>> @@ -120,11 +121,24 @@ unsigned int flush_area_local(const void *va, unsigned 
>> int flags)
>>          else
>>          {
>>              u32 t = pre_flush();
>> -            unsigned long cr4 = read_cr4();
>>  
>> -            write_cr4(cr4 & ~X86_CR4_PGE);
>> -            barrier();
>> -            write_cr4(cr4);
>> +            if ( !cpu_has_invpcid )
>> +            {
>> +                unsigned long cr4 = read_cr4();
>> +
>> +                write_cr4(cr4 & ~X86_CR4_PGE);
>> +                barrier();
>> +                write_cr4(cr4);
>> +            }
>> +            else
>> +            {
>> +                /*
>> +                 * Using invpcid to flush all mappings works
>> +                 * regardless of whether PCID is enabled or not.
>> +                 * It is faster than read-modify-write CR4.
>> +                 */
>> +                invpcid_flush_all();
>> +            }
> 
> As just validly indicated by Jürgen, this is where my comment I
> gave to one of his patches actually belongs: This is correct for
> FLUSH_TLB_GLOBAL, but goes too far for FLUSH_TLB.

And again it was so even before this patch.


Juergen

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