linux-kernel - [PATCH v7 09/12] KVM: x86/pmu: Constrain the num of guest counters with kvm_pmu

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Date:   Fri,  2 Jun 2023 18:10:55 -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,
        Like Xu <like.xu.linux@...il.com>,
        Like Xu <likexu@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sandipan Das <sandipan.das@....com>
Subject: [PATCH v7 09/12] KVM: x86/pmu: Constrain the num of guest counters
 with kvm_pmu_cap

From: Like Xu <likexu@...cent.com>

Cap the number of general purpose counters enumerated on AMD to what KVM
actually supports, i.e. don't allow userspace to coerce KVM into thinking
there are more counters than actually exist, e.g. by enumerating
X86_FEATURE_PERFCTR_CORE in guest CPUID when its not supported.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Like Xu <likexu@...cent.com>
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/pmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index e5c69062a909..c03958063a76 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -170,6 +170,9 @@ static void amd_pmu_refresh(struct kvm_vcpu *vcpu)
 	else
 		pmu->nr_arch_gp_counters = AMD64_NUM_COUNTERS;
 
+	pmu->nr_arch_gp_counters = min_t(unsigned int, pmu->nr_arch_gp_counters,
+					 kvm_pmu_cap.num_counters_gp);
+
 	pmu->counter_bitmask[KVM_PMC_GP] = ((u64)1 << 48) - 1;
 	pmu->reserved_bits = 0xfffffff000280000ull;
 	pmu->raw_event_mask = AMD64_RAW_EVENT_MASK;
-- 
2.41.0.rc2.161.g9c6817b8e7-goog