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

[Eric Hankland <ehankland@google.com>]

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@google.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)