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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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