From: Sandipan Das sandipan.das@amd.com
On AMD platforms, there is no way to restore PerfCntrGlobalCtl at VM-Entry or clear it at VM-Exit. Since the register states will be restored before entering and saved after exiting guest context, the counters can keep ticking and even overflow leading to chaos while still in host context.
To avoid this, intecept event selectors, which is already done by mediated PMU. In addition, always set the GuestOnly bit and clear the HostOnly bit for PMU selectors on AMD. Doing so allows the counters run only in guest context even if their enable bits are still set after VM exit and before host/guest PMU context switch.
Signed-off-by: Sandipan Das sandipan.das@amd.com Signed-off-by: Mingwei Zhang mizhang@google.com --- arch/x86/kvm/svm/pmu.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c index 9feaca739b96..1a7e3a897fdf 100644 --- a/arch/x86/kvm/svm/pmu.c +++ b/arch/x86/kvm/svm/pmu.c @@ -165,7 +165,8 @@ static int amd_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) data &= ~pmu->reserved_bits; if (data != pmc->eventsel) { pmc->eventsel = data; - pmc->eventsel_hw = data; + pmc->eventsel_hw = (data & ~AMD64_EVENTSEL_HOSTONLY) | + AMD64_EVENTSEL_GUESTONLY; kvm_pmu_request_counter_reprogram(pmc); } return 0;