linux-kernel - [PATCH v6 03/20] KVM: x86/pmu: Don't enumerate arch events KVM doesn't support

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Message-ID: <20231104000239.367005-4-seanjc@google.com>
Date:   Fri,  3 Nov 2023 17:02:21 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kan Liang <kan.liang@...ux.intel.com>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Like Xu <likexu@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>
Subject: [PATCH v6 03/20] KVM: x86/pmu: Don't enumerate arch events KVM
 doesn't support

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".

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@...gle.com>
---
 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