6.5-stable review patch. If anyone has any objections, please let me know.
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From: Roman Kagan rkagan@amazon.de
commit b29a2acd36dd7a33c63f260df738fb96baa3d4f8 upstream.
Performance counters are defined to have width less than 64 bits. The vPMU code maintains the counters in u64 variables but assumes the value to fit within the defined width. However, for Intel non-full-width counters (MSR_IA32_PERFCTRx) the value receieved from the guest is truncated to 32 bits and then sign-extended to full 64 bits. If a negative value is set, it's sign-extended to 64 bits, but then in kvm_pmu_incr_counter() it's incremented, truncated, and compared to the previous value for overflow detection.
That previous value is not truncated, so it always evaluates bigger than the truncated new one, and a PMI is injected. If the PMI handler writes a negative counter value itself, the vCPU never quits the PMI loop.
Turns out that Linux PMI handler actually does write the counter with the value just read with RDPMC, so when no full-width support is exposed via MSR_IA32_PERF_CAPABILITIES, and the guest initializes the counter to a negative value, it locks up.
This has been observed in the field, for example, when the guest configures atop to use perfevents and runs two instances of it simultaneously.
To address the problem, maintain the invariant that the counter value always fits in the defined bit width, by truncating the received value in the respective set_msr methods. For better readability, factor the out into a helper function, pmc_write_counter(), shared by vmx and svm parts.
Fixes: 9cd803d496e7 ("KVM: x86: Update vPMCs when retiring instructions") Cc: stable@vger.kernel.org Signed-off-by: Roman Kagan rkagan@amazon.de Link: https://lore.kernel.org/all/20230504120042.785651-1-rkagan@amazon.de Tested-by: Like Xu likexu@tencent.com [sean: tweak changelog, s/set/write in the helper] Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/pmu.h | 6 ++++++ arch/x86/kvm/svm/pmu.c | 2 +- arch/x86/kvm/vmx/pmu_intel.c | 4 ++-- 3 files changed, 9 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/pmu.h +++ b/arch/x86/kvm/pmu.h @@ -74,6 +74,12 @@ static inline u64 pmc_read_counter(struc return counter & pmc_bitmask(pmc); }
+static inline void pmc_write_counter(struct kvm_pmc *pmc, u64 val) +{ + pmc->counter += val - pmc_read_counter(pmc); + pmc->counter &= pmc_bitmask(pmc); +} + static inline void pmc_release_perf_event(struct kvm_pmc *pmc) { if (pmc->perf_event) { --- a/arch/x86/kvm/svm/pmu.c +++ b/arch/x86/kvm/svm/pmu.c @@ -160,7 +160,7 @@ static int amd_pmu_set_msr(struct kvm_vc /* MSR_PERFCTRn */ pmc = get_gp_pmc_amd(pmu, msr, PMU_TYPE_COUNTER); if (pmc) { - pmc->counter += data - pmc_read_counter(pmc); + pmc_write_counter(pmc, data); pmc_update_sample_period(pmc); return 0; } --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -406,11 +406,11 @@ static int intel_pmu_set_msr(struct kvm_ if (!msr_info->host_initiated && !(msr & MSR_PMC_FULL_WIDTH_BIT)) data = (s64)(s32)data; - pmc->counter += data - pmc_read_counter(pmc); + pmc_write_counter(pmc, data); pmc_update_sample_period(pmc); break; } else if ((pmc = get_fixed_pmc(pmu, msr))) { - pmc->counter += data - pmc_read_counter(pmc); + pmc_write_counter(pmc, data); pmc_update_sample_period(pmc); break; } else if ((pmc = get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0))) {