Re: [PATCH V4 4/4] KVM: selftests: Add perf_metrics and fixed counter 3 tests

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] KVM's emulator unconditionally injects a #GP on guest accesses to MSR_PERF_METRICS, breaking instruction emulation and nested virtualization. The selftest omits forced emulation coverage that would expose this.
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commit f588cce382d8777ebda7951bd3447ee7ba4c18ff
Author: Zide Chen <zide.chen@intel.com>

KVM: selftests: Add perf_metrics and fixed counter 3 tests
    
Add a selftest to exercise IA32_PERF_METRICS, i.e. architectural
support for Topdown (TMA) Level 1 metrics, enumerated by
IA32_PERF_CAPABILITIES[15].

> diff --git a/tools/testing/selftests/kvm/x86/pmu_counters_test.c b/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> index dc6afac3aa919..d4688a7d1e556 100644
> --- a/tools/testing/selftests/kvm/x86/pmu_counters_test.c
> +++ b/tools/testing/selftests/kvm/x86/pmu_counters_test.c

[ ... ]

> @@ -318,6 +322,56 @@ static void guest_test_arch_event(u8 idx)
>  				FIXED_PMC_GLOBAL_CTRL_ENABLE(i));
>  }
>  
> +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_ASSERT_EQ(rdmsr(MSR_PERF_METRICS), 0xdeaddead);
> +}

[Severity: High]
Should this test include forced emulation (e.g., using KVM_FEP) coverage for
these MSR_PERF_METRICS accesses?

Currently, the selftest relies purely on native rdmsr/wrmsr execution.
If these instructions were emulated, it would expose an issue in
intel_pmu_get_msr() and intel_pmu_set_msr() where KVM's emulator
unconditionally injects a #GP on guest accesses because they return 1
when !msr_info->host_initiated.

Could we add forced emulation coverage to catch emulator issues that break
instruction emulation and nested virtualization?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260623041927.178256-1-zide.chen@intel.com?part=4