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KVM: selftests: Add regression test for mediated PMU fixed counter filter bug

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Add a regression test where KVM would inadvertently ignore PMU event
filters on writes that change _some_ bits in FIXED_CTR_CTRL, but not the
enable bits for PMCs that are denied to the guest.

Link: https://patch.msgid.link/20260603231905.1738487-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2026-06-03 16:19:05 -07:00
parent 9c6e2463c9
commit 2c725bd280
1 changed files with 6 additions and 0 deletions
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6
tools/testing/selftests/kvm/x86/pmu_event_filter_test.c
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@ -731,6 +731,8 @@ static void test_filter_ioctl(struct kvm_vcpu *vcpu)
static void intel_run_fixed_counter_guest_code(u8 idx)
{
u8 nr_fixed_counters = this_cpu_property(X86_PROPERTY_PMU_NR_FIXED_COUNTERS);
for (;;) {
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0);
wrmsr(MSR_CORE_PERF_FIXED_CTR0 + idx, 0);
@ -738,6 +740,10 @@ static void intel_run_fixed_counter_guest_code(u8 idx)
/* Only OS_EN bit is enabled for fixed counter[idx]. */
wrmsr(MSR_CORE_PERF_FIXED_CTR_CTRL, FIXED_PMC_CTRL(idx, FIXED_PMC_KERNEL));
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, FIXED_PMC_GLOBAL_CTRL_ENABLE(idx));
if (nr_fixed_counters > 1)
wrmsr(MSR_CORE_PERF_FIXED_CTR_CTRL,
FIXED_PMC_CTRL(idx, FIXED_PMC_KERNEL) |
FIXED_PMC_CTRL((idx + 1) % nr_fixed_counters, FIXED_PMC_KERNEL));
__asm__ __volatile__("loop ." : "+c"((int){NUM_BRANCHES}));
wrmsr(MSR_CORE_PERF_GLOBAL_CTRL, 0);