On 11/17/2017 5:44 AM, Borislav Petkov wrote:
> On Thu, Nov 16, 2017 at 12:00:11PM -0600, Natarajan, Janakarajan wrote:
>> Ah my apologies. So when the pmu is initialized the cpuid entries
>> aren't available then.
> So let's see:
>
> ... kvm_arch_vcpu_create() ->
> svm_create_vcpu() ->
> kvm_vcpu_init() ->
> kvm_arch_vcpu_init() ->
>
> <--- HERE
>
> kvm_pmu_init()
>
> But at HERE in kvm_arch_vcpu_init() right before kvm_pmu_init() we do already query
> cpuid:
>
> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>
> so it's not like we don't know about cpuid leafs at that point. Which
> would mean that the code can be made to set the CPU family earlier,
> before kvm_pmu_init() runs so that you have the proper CPU family and
> thus have this thing properly designed.
>
> Maybe Paolo and Radim have a better suggestion here...
Paolo, Radim any suggestions about this. I feel that the number of
counters initialized can be 6
and the subsequent code (kvm_pmu_refresh()) takes care of the number of
counters to be used (4 or 6)
based on the vcpu family.
>
2017-12-01 13:30-0600, Natarajan, Janakarajan:
> On 11/17/2017 5:44 AM, Borislav Petkov wrote:
> > On Thu, Nov 16, 2017 at 12:00:11PM -0600, Natarajan, Janakarajan wrote:
> > > Ah my apologies. So when the pmu is initialized the cpuid entries
> > > aren't available then.
> > So let's see:
> >
> > ... kvm_arch_vcpu_create() ->
> > svm_create_vcpu() ->
> > kvm_vcpu_init() ->
> > kvm_arch_vcpu_init() ->
> >
> > <--- HERE
> >
> > kvm_pmu_init()
> >
> > But at HERE in kvm_arch_vcpu_init() right before kvm_pmu_init() we do already query
> > cpuid:
> >
> > vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
> >
> > so it's not like we don't know about cpuid leafs at that point. Which
> > would mean that the code can be made to set the CPU family earlier,
> > before kvm_pmu_init() runs so that you have the proper CPU family and
> > thus have this thing properly designed.
> >
> > Maybe Paolo and Radim have a better suggestion here...
>
> Paolo, Radim any suggestions about this. I feel that the number of counters
> initialized can be 6
This is the best solution with the current framework.
> and the subsequent code (kvm_pmu_refresh()) takes care of the number of
> counters to be used (4 or 6)
> based on the vcpu family.
Can't we look only at X86_FEATURE_PERFCTR_CORE and completely ignore the
AMD family?
Using the family would bring problems with compatiblity.
Thanks.
On 12/5/2017 11:56 AM, Radim Krcmar wrote:
> 2017-12-01 13:30-0600, Natarajan, Janakarajan:
>> On 11/17/2017 5:44 AM, Borislav Petkov wrote:
>>> On Thu, Nov 16, 2017 at 12:00:11PM -0600, Natarajan, Janakarajan wrote:
>>>> Ah my apologies. So when the pmu is initialized the cpuid entries
>>>> aren't available then.
>>> So let's see:
>>>
>>> ... kvm_arch_vcpu_create() ->
>>> svm_create_vcpu() ->
>>> kvm_vcpu_init() ->
>>> kvm_arch_vcpu_init() ->
>>>
>>> <--- HERE
>>>
>>> kvm_pmu_init()
>>>
>>> But at HERE in kvm_arch_vcpu_init() right before kvm_pmu_init() we do already query
>>> cpuid:
>>>
>>> vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
>>>
>>> so it's not like we don't know about cpuid leafs at that point. Which
>>> would mean that the code can be made to set the CPU family earlier,
>>> before kvm_pmu_init() runs so that you have the proper CPU family and
>>> thus have this thing properly designed.
>>>
>>> Maybe Paolo and Radim have a better suggestion here...
>> Paolo, Radim any suggestions about this. I feel that the number of counters
>> initialized can be 6
> This is the best solution with the current framework.
Okay.
>
>> and the subsequent code (kvm_pmu_refresh()) takes care of the number of
>> counters to be used (4 or 6)
>> based on the vcpu family.
> Can't we look only at X86_FEATURE_PERFCTR_CORE and completely ignore the
> AMD family?
> Using the family would bring problems with compatiblity.
Yeah. We can just use the X86_FEATURE_PERFCTR_CORE flag as a check. I'll
send a v3
with the changes.
Thanks.
>
> Thanks.