On 11/10/2023 10:12 AM, Sean Christopherson wrote:
Inject #GP on RDPMC if the "fast" flag is set for architectural Intel PMUs, i.e. if the PMU version is non-zero. Per Intel's SDM, and confirmed on bare metal, the "fast" flag is supported only for non-architectural PMUs, and is reserved for architectural PMUs. If the processor does not support architectural performance monitoring (CPUID.0AH:EAX[7:0]=0), ECX[30:0] specifies the index of the PMC to be read. Setting ECX[31] selects “fast” read mode if supported. In this mode, RDPMC returns bits 31:0 of the PMC in EAX while clearing EDX to zero. If the processor does support architectural performance monitoring (CPUID.0AH:EAX[7:0] ≠ 0), ECX[31:16] specifies type of PMC while ECX[15:0] specifies the index of the PMC to be read within that type. The following PMC types are currently defined: — General-purpose counters use type 0. The index x (to read IA32_PMCx) must be less than the value enumerated by CPUID.0AH.EAX[15:8] (thus ECX[15:8] must be zero). — Fixed-function counters use type 4000H. The index x (to read IA32_FIXED_CTRx) can be used if either CPUID.0AH.EDX[4:0] > x or CPUID.0AH.ECX[x] = 1 (thus ECX[15:5] must be 0). — Performance metrics use type 2000H. This type can be used only if IA32_PERF_CAPABILITIES.PERF_METRICS_AVAILABLE[bit 15]=1. For this type, the index in ECX[15:0] is implementation specific. WARN if KVM ever actually tries to complete RDPMC for a non-architectural PMU as KVM doesn't support such PMUs, i.e. kvm_pmu_rdpmc() should reject the RDPMC before getting to the Intel code. Fixes: f5132b01386b ("KVM: Expose a version 2 architectural PMU to a guests") Fixes: 67f4d4288c35 ("KVM: x86: rdpmc emulation checks the counter incorrectly") Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/vmx/pmu_intel.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c index c6ea128ea7c8..80255f86072e 100644 --- a/arch/x86/kvm/vmx/pmu_intel.c +++ b/arch/x86/kvm/vmx/pmu_intel.c @@ -61,7 +61,19 @@ static struct kvm_pmc *intel_pmc_idx_to_pmc(struct kvm_pmu *pmu, int pmc_idx)static u32 intel_rdpmc_get_masked_idx(struct kvm_pmu *pmu, u32 idx){ - return idx & ~(INTEL_RDPMC_FIXED | INTEL_RDPMC_FAST); + /* + * Fast RDPMC is only supported on non-architectural PMUs, which KVM + * doesn't support. + */ + if (WARN_ON_ONCE(!pmu->version)) + return idx & ~INTEL_RDPMC_FAST; + + /* + * Fixed PMCs are supported on all architectural PMUs. Note, KVM only + * emulates fixed PMCs for PMU v2+, but the flag itself is still valid, + * i.e. let RDPMC fail due to accessing a non-existent counter. + */ + return idx & ~INTEL_RDPMC_FIXED; }static bool intel_is_valid_rdpmc_ecx(struct kvm_vcpu *vcpu, unsigned int idx)
Reviewed-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
