linux-kernel - [PATCH v9 10/28] KVM: x86/pmu: Explicitly check for RDPMC of unsupported Intel PMC types

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Message-ID: <20231202000417.922113-11-seanjc@google.com>
Date:   Fri,  1 Dec 2023 16:03:59 -0800
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>,
        Jim Mattson <jmattson@...gle.com>,
        Jinrong Liang <cloudliang@...cent.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        Like Xu <likexu@...cent.com>
Subject: [PATCH v9 10/28] KVM: x86/pmu: Explicitly check for RDPMC of
 unsupported Intel PMC types

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@...gle.com>
---
 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)
+		return NULL;
+
+	idx &= INTEL_RDPMC_INDEX_MASK;
 	if (fixed) {
 		counters = pmu->fixed_counters;
 		num_counters = pmu->nr_arch_fixed_counters;
-- 
2.43.0.rc2.451.g8631bc7472-goog