On Fri, Nov 3, 2023 at 5:02 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > Don't advertise support to userspace for architectural events that KVM > doesn't support, i.e. for "real" events that aren't listed in > intel_pmu_architectural_events. On current hardware, this effectively > means "don't advertise support for Top Down Slots". NR_REAL_INTEL_ARCH_EVENTS is only used in intel_hw_event_available(). As discussed (https://lore.kernel.org/kvm/ZUU12-TUR_1cj47u@xxxxxxxxxx/), intel_hw_event_available() should go away. Aside from mapping fixed counters to event selector and unit mask (fixed_pmc_events[]), KVM has no reason to know when a new architectural event is defined. The variable that this change "fixes" is only used to feed CPUID.0AH:EBX in KVM_GET_SUPPORTED_CPUID, and kvm_pmu_cap.events_mask is already constructed from what host perf advertises support for. > Mask off the associated "unavailable" bits, as said bits for undefined > events are reserved to zero. Arguably the events _are_ defined, but from > a KVM perspective they might as well not exist, and there's absolutely no > reason to leave useless unavailable bits set. > > Fixes: a6c06ed1a60a ("KVM: Expose the architectural performance monitoring CPUID leaf") > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> > --- > arch/x86/kvm/vmx/pmu_intel.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > index 3316fdea212a..8d545f84dc4a 100644 > --- a/arch/x86/kvm/vmx/pmu_intel.c > +++ b/arch/x86/kvm/vmx/pmu_intel.c > @@ -73,6 +73,15 @@ static void intel_init_pmu_capability(void) > int i; > > /* > + * Do not enumerate support for architectural events that KVM doesn't > + * support. Clear unsupported events "unavailable" bit as well, as > + * architecturally such bits are reserved to zero. > + */ > + kvm_pmu_cap.events_mask_len = min(kvm_pmu_cap.events_mask_len, > + NR_REAL_INTEL_ARCH_EVENTS); > + kvm_pmu_cap.events_mask &= GENMASK(kvm_pmu_cap.events_mask_len - 1, 0); > + > + /* > * Perf may (sadly) back a guest fixed counter with a general purpose > * counter, and so KVM must hide fixed counters whose associated > * architectural event are unsupported. On real hardware, this should > -- > 2.42.0.869.gea05f2083d-goog >
