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 05:57:48AM -0700, Jan Beulich wrote:
> >>> On 05.03.18 at 13:49, <jgross@xxxxxxxx> wrote:
> > On 05/03/18 13:37, Jan Beulich wrote:
> >>>>> On 05.03.18 at 12:43, <jgross@xxxxxxxx> wrote:
> >>> On 05/03/18 12:20, 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'd rather keep this message. As we are hiding PCID and INPCID from dom0
> >>> this is the only indicator of those features being supported. In case of
> >>> an error related to TLB consistency this information is important IMO.
> >> 
> >> Well, this argument would hold for almost every other advanced
> >> feature we use.
> > 
> > Then I'd suggest to either add individual messages for those features or
> > to have a single message (or a few) to list all features like the flags
> > in /proc/cpuinfo. This list could even be part of the "xl info" output.
> 
> I have no idea whether there are plans to make this part of
> "xl info" output; xen-cpuid certainly can tell you.
> 
> Wei, btw - for the case of there being problems with this new use
> of INVPCID, perhaps you will also want to extend parse_xen_cpuid()
> so that the use can be disabled from the command line.
> 

Noted.

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