Re: [PATCH] kvm: x86: Add Intel PMU MSRs to msrs_to_save[]

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 27/09/19 15:53, Vitaly Kuznetsov wrote:
>> Paolo Bonzini <pbonzini@redhat.com> writes:
>> 
>>> Queued, thanks.
>> 
>> I'm sorry for late feedback but this commit seems to be causing
>> selftests failures for me, e.g.:
>> 
>> # ./x86_64/state_test 
>> Testing guest mode: PA-bits:ANY, VA-bits:48,  4K pages
>> Guest physical address width detected: 46
>> ==== Test Assertion Failure ====
>>   lib/x86_64/processor.c:1089: r == nmsrs
>>   pid=14431 tid=14431 - Argument list too long
>>      1	0x000000000040a55f: vcpu_save_state at processor.c:1088 (discriminator 3)
>>      2	0x00000000004010e3: main at state_test.c:171 (discriminator 4)
>>      3	0x00007f881eb453d4: ?? ??:0
>>      4	0x0000000000401287: _start at ??:?
>>   Unexpected result from KVM_GET_MSRS, r: 36 (failed at 194)
>> 
>> Is this something known already or should I investigate?
>
> No, I didn't know about it, it works here.
>

Ok, this is a bit weird :-) '194' is 'MSR_ARCH_PERFMON_EVENTSEL0 +
14'. In intel_pmu_refresh() nr_arch_gp_counters is set to '8', however,
rdmsr_safe() for this MSR passes in kvm_init_msr_list() (but it fails
for 0x18e..0x193!) so it stay in the list. get_gp_pmc(), however, checks
it against nr_arch_gp_counters and returns a failure.

Oh, btw, this is Intel(R) Xeon(R) CPU E5-2603 v3

So apparently rdmsr_safe() check in kvm_init_msr_list() is not enough,
for PMU MSRs we need to do extra.

-- 
Vitaly