On 1/10/2024 7:02 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.
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/vmx/pmu_intel.c | 21 +++++++++++++++------
> 1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
> index c37dd3aa056b..b41bdb0a0995 100644
> --- a/arch/x86/kvm/vmx/pmu_intel.c
> +++ b/arch/x86/kvm/vmx/pmu_intel.c
> @@ -26,6 +26,7 @@
> * further confuse things, non-architectural PMUs use bit 31 as a flag for
> * "fast" reads, whereas the "type" is an explicit value.
> */
> +#define INTEL_RDPMC_GP 0
> #define INTEL_RDPMC_FIXED INTEL_PMC_FIXED_RDPMC_BASE
>
> #define INTEL_RDPMC_TYPE_MASK GENMASK(31, 16)
> @@ -89,21 +90,29 @@ static struct kvm_pmc *intel_rdpmc_ecx_to_pmc(struct kvm_vcpu *vcpu,
> return NULL;
>
> /*
> - * 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.
> + * General Purpose (GP) PMCs are supported on all PMUs, and fixed PMCs
> + * are supported on all architectural PMUs, i.e. on all virtual PMUs
> + * supported by KVM. Note, KVM only emulates fixed PMCs for PMU v2+,
> + * but the type itself is still valid, 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 (type == INTEL_RDPMC_FIXED) {
> + switch (type) {
> + case INTEL_RDPMC_FIXED:
> counters = pmu->fixed_counters;
> num_counters = pmu->nr_arch_fixed_counters;
> bitmask = pmu->counter_bitmask[KVM_PMC_FIXED];
> - } else {
> + break;
> + case INTEL_RDPMC_GP:
> counters = pmu->gp_counters;
> num_counters = pmu->nr_arch_gp_counters;
> bitmask = pmu->counter_bitmask[KVM_PMC_GP];
> + break;
> + default:
> + return NULL;
> }
>
> + idx &= INTEL_RDPMC_INDEX_MASK;
> if (idx >= num_counters)
> return NULL;
>
Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>