Re: [Xen-devel] [PATCH 1/2] x86: report if PCID and INVPCID are supported

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Mar 05, 2018 at 04:20:48AM -0700, Jan Beulich wrote:
> >>> On 05.03.18 at 10:50, <wei.liu2@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/setup.c
> > +++ b/xen/arch/x86/setup.c
> > @@ -1701,6 +1701,13 @@ void __init noreturn __start_xen(unsigned long mbi_p)
> >             cpu_has_nx ? XENLOG_INFO : XENLOG_WARNING "Warning: ",
> >             cpu_has_nx ? "" : "not ");
> >  
> > +
> > +    printk(XENLOG_INFO
> > +           "PCID (Process-Context IDentifier) %ssupported\n",
> > +           cpu_has_pcid ? "" : "not ");
> > +
> > +    printk(XENLOG_INFO "INVPCID %ssupported\n", cpu_has_invpcid ? "" : 
> > "not ");
> 
> Do we really need this? We log a message for NX as an exception,
> we don't do so for other features (and things would get pretty
> unwieldy if we did).
> 

I'm not too fuss really. It helped me to pick a machine when I didn't
have the exact spec of the pool of machines. The same information can
certainly be obtained from hardware cpuid info.

On another note, what is the most reliable way to extract hardware cpuid
info from Xen? AIUI now cpuid faulting can be enabled for both PV and
HVM guests so running cpuid in PV guests might not return the real bits
(which is a good thing).

Wei.

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