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

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.
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--- 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.

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?

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=8