Re: [PATCH v8 8/8] KVM: selftests: Add PERF_METRICS and fixed counter 3 tests

On 8/17/2026 1:57 PM, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Unhandled #GP / Selftest Crash when writing 0xdeaddead to MSR_PERF_METRICS.
> --
> 
> --- Patch [8]: [PATCH v8 8/8] KVM: selftests: Add PERF_METRICS and fixed counter 3 tests ---
> commit 19d6869fac1fbdcc63ff54623403cec33b922848
> Author: Zide Chen <[email protected]>
> 
> KVM: selftests: Add PERF_METRICS and fixed counter 3 tests
> 
> This commit adds a test case to exercise IA32_PERF_METRICS for Topdown
> (TMA) Level 1 metrics and extends the PMU selftest to cover Intel fixed
> counter 3.
> 
>> diff --git a/tools/testing/selftests/kvm/x86/pmu_counters_test.c b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
>> --- a/tools/testing/selftests/kvm/x86/pmu_counters_test.c
>> +++ b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> [ ... ]
>> +static void __guest_test_perf_metrics(void)
>> +{
> [ ... ]
>> +	/* Sanity check after PERF_METRICS disabled. */
>> +	__asm__ __volatile__("loop ." : "+c"((int){NUM_LOOPS}));
>> +	GUEST_ASSERT_EQ(rdmsr(MSR_PERF_METRICS), metrics);
>> +	wrmsr(MSR_PERF_METRICS, 0xdeaddead);
>> +
>> +	guest_test_rdpmc(INTEL_RDPMC_METRICS, true, 0xdeaddead);
>> +}
> 
> [Severity: Medium]
> Will this wrmsr(MSR_PERF_METRICS, 0xdeaddead) cause an unhandled #GP and
> crash the selftest on hosts with Mediated PMU pass-through?
> 
> Writing an architecturally invalid non-zero value to MSR_PERF_METRICS
> generates a #GP on real hardware. Under Mediated PMU, KVM configures the
> VMCS to pass-through MSR accesses directly to hardware, so this fault
> would be injected into the guest.

0xdeaddead is a valid non-zero value. So this statement is supposed to
work well.

> 
> If the hardware silently discards the write instead of faulting, will the
> subsequent guest_test_rdpmc() assertion fail because it expects to read back
> 0xdeaddead, while the hardware holds the previous value?
>