Re: Biweekly KVM Test report, kernel 0c7771... userspace 1223a0...

[Avi Kivity <avi@redhat.com>]

Amit Shah wrote:
>>
>>>         /*
>>>          * Check whether the Architectural PerfMon supports
>>>          * Unhalted Core Cycles Event or not.
>>>          * NOTE: Corresponding bit = 0 in ebx indicates event present.
>>>          */
>>>         cpuid(10, &(eax.full), &ebx, &unused, &unused);
>>>         if ((eax.split.mask_length <  
>>> (ARCH_PERFMON_UNHALTED_CORE_CYCLES_INDEX+1)) ||
>>>             (ebx & ARCH_PERFMON_UNHALTED_CORE_CYCLES_PRESENT))
>>>                 return 0;
>>>
>>>       
>> So I think it can be done.
>>     
>
> Only if the guest kernel (or module accessing those registers) look at
> the cpuid output, right? I checked this for the Kaspersky AV on Windows,
> the crash bug I was solving and that program doesn't seem to check
> cpuid.
>   

The only way to solve all possible cases is to implement the performance 
counters MSRs.  That's not going to happen in a hurry, we're looking at 
making the known cases work.

> RHEL 5.3 is based on 2.6.18 and this patch appears to have entered in
> 2.6.21. I saw this on 5.3 as well.
>   

The snippet I quoted came from RHEL 5.3.  It checks cpuid so we should 
be able to make it fail gracefully.

-- 
error compiling committee.c: too many arguments to function