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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

> @@ -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.

Jan


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