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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/03/18 11:31, Wei Liu wrote:
> 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).

For now, `xen-cpuid`, which uses SYSCTL_get_cpufeatureset internally.

This will shortly be changing to get the fully cpuid/msr policies rather
than just the feature bitmaps.

~Andrew

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