Re: [Xen-devel] [PATCH v3 4/7] xen/x86: use invpcid for flushing the TLB

[Juergen Gross <jgross@xxxxxxxx>]

On 22/03/18 16:35, Jan Beulich wrote:
>>>> On 21.03.18 at 13:51, <jgross@xxxxxxxx> wrote:
>> --- a/docs/misc/xen-command-line.markdown
>> +++ b/docs/misc/xen-command-line.markdown
>> @@ -1380,6 +1380,14 @@ Because responsibility for APIC setup is shared 
>> between Xen and the
>>  domain 0 kernel this option is automatically propagated to the domain
>>  0 command line.
>>  
>> +### noinvpcid (x86)
>> +> `= <boolean>`
>> +
>> +Disable using the INVPCID instruction for flushing TLB entries.
>> +This should only be used in case of known issues on the current platform
>> +with that instruction. Disabling INVPCID will normally result in a slightly
>> +degraded performance.
> 
> At the first glance this looks as if it wants to be a cpuid=
> sub-option. However, that would disable use by both Xen and
> (HVM) guests. Andrew, what are your plans here as to
> distinguishing the "Xen uses a feature" from the "disable use of
> a feature altogether"?
> 
> If we stay with a separate option, then please make this a
> normal boolean one (i.e. drop the "no" prefix), as "no-noinvpcid"
> is rather ugly.

Okay.

> 
>> @@ -457,7 +472,6 @@ static void generic_set_all(void)
>>                      set_bit(count, &smp_changes_mask);
>>              mask >>= 1;
>>      }
>> -    
>>  }
>>  
>>  static void generic_set_mtrr(unsigned int reg, unsigned long base,
> 
> I don't mind this line being dropped, but in general please avoid
> stray changes which aren't assimilated into changes you do anyway.

The main reason I did drop this line was the trailing tab. I just took
the risk of someone complaining.


Juergen


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