On Mon, Dec 11, 2023, Jim Mattson wrote: > On Sun, Dec 10, 2023 at 10:26 PM Mi, Dapeng <dapeng1.mi@xxxxxxxxxxxxxxx> wrote: > > > > > > On 12/2/2023 8:03 AM, Sean Christopherson wrote: > > > Explicitly check for attempts to read unsupported PMC types instead of > > > letting the bounds check fail. Functionally, letting the check fail is > > > ok, but it's unnecessarily subtle and does a poor job of documenting the > > > architectural behavior that KVM is emulating. > > > > > > Opportunistically add macros for the type vs. index to further document > > > what is going on. > > > > > > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > > > --- > > > arch/x86/kvm/vmx/pmu_intel.c | 11 +++++++++-- > > > 1 file changed, 9 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > > > index 644de27bd48a..bd4f4bdf5419 100644 > > > --- a/arch/x86/kvm/vmx/pmu_intel.c > > > +++ b/arch/x86/kvm/vmx/pmu_intel.c > > > @@ -23,6 +23,9 @@ > > > /* Perf's "BASE" is wildly misleading, this is a single-bit flag, not a base. */ > > > #define INTEL_RDPMC_FIXED INTEL_PMC_FIXED_RDPMC_BASE > > > > > > +#define INTEL_RDPMC_TYPE_MASK GENMASK(31, 16) > > > +#define INTEL_RDPMC_INDEX_MASK GENMASK(15, 0) > > > + > > > #define MSR_PMC_FULL_WIDTH_BIT (MSR_IA32_PMC0 - MSR_IA32_PERFCTR0) > > > > > > static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data) > > > @@ -82,9 +85,13 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu, > > > /* > > > * 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. > > > + * i.e. let RDPMC fail due to accessing a non-existent counter. Reject > > > + * attempts to read all other types, which are unknown/unsupported. > > > */ > > > - idx &= ~INTEL_RDPMC_FIXED; > > > + if (idx & INTEL_RDPMC_TYPE_MASK & ~INTEL_RDPMC_FIXED) > > You know how I hate to be pedantic (ROFL), but the SDM only says: > > 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. > > It does not say that the types are bitwise-exclusive. > > Yes, the types defined thus far are bitwise-exclusive, but who knows > what tomorrow may bring? The goal isn't to make the types exclusive, the goal is to reject types that aren't supported by KVM. The above accomplishes that, no? I don't see how KVM could get a false negative or false positive, the above allows exactly FIXED and "none" types. Or are you objecting to the comment?
