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[RFC,v3,53/58] KVM: x86/pmu/svm: Set GuestOnly bit and clear HostOnly bit when guest write to event selectors

Message ID 20240801045907.4010984-54-mizhang@google.com (mailing list archive)
State New, archived
Headers show
Series Mediated Passthrough vPMU 3.0 for x86 | expand

Commit Message

Mingwei Zhang Aug. 1, 2024, 4:59 a.m. UTC 
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, the PERF_CTLx MSRs (event selectors) are always
intercepted. KVM will always set the GuestOnly bit and clear the
HostOnly bit so that the counters run only in guest context even if
their enable bits are set. Intercepting these MSRs is also necessary
for guest event filtering.

Signed-off-by: Sandipan Das <sandipan.das@amd.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
---
 arch/x86/kvm/svm/pmu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
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Patch

diff --git a/arch/x86/kvm/svm/pmu.c b/arch/x86/kvm/svm/pmu.c
index cc03c3e9941f..2b7cc7616162 100644
--- a/arch/x86/kvm/svm/pmu.c
+++ b/arch/x86/kvm/svm/pmu.c
@@ -165,7 +165,12 @@  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;
-			kvm_pmu_request_counter_reprogram(pmc);
+			if (is_passthrough_pmu_enabled(vcpu)) {
+				data &= ~AMD64_EVENTSEL_HOSTONLY;
+				pmc->eventsel_hw = data | AMD64_EVENTSEL_GUESTONLY;
+			} else {
+				kvm_pmu_request_counter_reprogram(pmc);
+			}
 		}
 		return 0;
 	}