linux-kernel - [PATCH] KVM: x86: Fix perfctr WRMSR for running counters

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Message-Id: <20200127212256.194310-1-ehankland@google.com>
Date:   Mon, 27 Jan 2020 13:22:56 -0800
From:   Eric Hankland <ehankland@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Shier <pshier@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Eric Hankland <ehankland@...gle.com>
Subject: [PATCH] KVM: x86: Fix perfctr WRMSR for running counters

Correct the logic in intel_pmu_set_msr() for fixed and general purpose
counters. This was recently changed to set pmc->counter without taking
in to account the value of pmc_read_counter() which will be incorrect if
the counter is currently running and non-zero; this changes back to the
old logic which accounted for the value of currently running counters.

Signed-off-by: Eric Hankland <ehankland@...gle.com>
---
 arch/x86/kvm/vmx/pmu_intel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 34a3a17bb6d7..9bdbe05b599c 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -264,9 +264,10 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 				pmc->counter = data;
 			else
 				pmc->counter = (s32)data;
+			pmc->counter += pmc->counter - pmc_read_counter(pmc);
 			return 0;
 		} else if ((pmc = get_fixed_pmc(pmu, msr))) {
-			pmc->counter = data;
+			pmc->counter += data - pmc_read_counter(pmc);
 			return 0;
 		} else if ((pmc = get_gp_pmc(pmu, msr, MSR_P6_EVNTSEL0))) {
 			if (data == pmc->eventsel)