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

["Jan Beulich" <jbeulich@suse.com>]

>>> Juergen Gross <jgross@suse.com> 03/09/18 7:05 PM >>>
>On 09/03/18 16:29, Jan Beulich wrote:
>>>>> On 05.03.18 at 10:50, <wei.liu2@citrix.com> 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.

Not exactly - "before this patch" should include the state things were in before
32-bit code got removed. And that's where we had a proper separation between
flushes including and excluding global entries. And now that we regain that
ability, we should leverage it.

Jan


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