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

[Juergen Gross <jgross@xxxxxxxx>]

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.


Juergen


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