Re: [PATCH 1/2] x86/VPMU: Support only versions 2 and 3 of architectural performance monitoring

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 12/01/2015 04:01 AM, Dietmar Hahn wrote:
> Am Montag 30 November 2015, 13:38:40 schrieb Boris Ostrovsky:
>> We need to have at least version 2 since it's the first version to
>> support various control and status registers (such as
>> MSR_CORE_PERF_GLOBAL_CTRL) that VPMU relies on always having.
>>
>> With explicit testing for PMU version we can now remove CPUID model
>> check.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> ---
>>   xen/arch/x86/cpu/vpmu_intel.c | 55 +++++++------------------------------------
>>   1 file changed, 8 insertions(+), 47 deletions(-)
>>
>> diff --git a/xen/arch/x86/cpu/vpmu_intel.c b/xen/arch/x86/cpu/vpmu_intel.c
>> index d5ea7fe..bb4ddcc 100644
>> --- a/xen/arch/x86/cpu/vpmu_intel.c
>> +++ b/xen/arch/x86/cpu/vpmu_intel.c
>> @@ -955,59 +955,20 @@ int vmx_vpmu_initialise(struct vcpu *v)
>>   int __init core2_vpmu_init(void)
>>   {
>>       u64 caps;
>> +    unsigned int version = 0;
>>   
>> -    if ( current_cpu_data.x86 != 6 )
>> +    if ( current_cpu_data.cpuid_level >= 0xa )
>> +        version = cpuid_eax(0xa) & 0xff;
>> +    if ( (version != 2) && (version != 3) )
>>       {
>> -        printk(XENLOG_WARNING "VPMU: only family 6 is supported\n");
>> +        printk(XENLOG_WARNING "VPMU: version %d is not supported\n", version);
>>           return -EINVAL;
> But this means that all (newer?) processors with version=4 are not supported
> even though the SDM 3B tells:
> "Processors supporting architectural performance monitoring version 4 also
>   supports version 1, 2, and 3, ..."
>
> Shold we not only write a hint that version 4 capabilities are not supported
> and fake this cpuid-flag for the guests to the version 3?

I in fact didn't know there was version 4 since I've always been looking 
at (apparently) old version of the SDM (Jan 2013).

We should indeed then downgrade version 4 to 3 as reported by .do_cpud() op.

-boris