[PATCH v4 27/38] KVM: x86/pmu: Handle PMU MSRs interception and event filtering

[Mingwei Zhang]

From: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

Mediated vPMU needs to intercept EVENTSELx and FIXED_CNTR_CTRL MSRs to
filter out guest malicious perf events. Either writing these MSRs or
updating event filters would call reprogram_counter() eventually. Thus
check if the guest event should be filtered out in reprogram_counter().
If so, clear corresponding EVENTSELx MSR or FIXED_CNTR_CTRL field to
ensure the guest event won't be really enabled at vm-entry.

Besides, mediated vPMU intercepts the MSRs of these guest not owned
counters and it just needs simply to read/write from/to pmc->counter.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
Co-developed-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
---
 arch/x86/kvm/pmu.c | 27 +++++++++++++++++++++++++++
 arch/x86/kvm/pmu.h |  3 +++
 2 files changed, 30 insertions(+)

diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
index 63143eeb5c44..e9100dc49fdc 100644
--- a/arch/x86/kvm/pmu.c
+++ b/arch/x86/kvm/pmu.c
@@ -305,6 +305,11 @@ static void pmc_update_sample_period(struct kvm_pmc *pmc)
 
 void pmc_write_counter(struct kvm_pmc *pmc, u64 val)
 {
+	if (kvm_mediated_pmu_enabled(pmc->vcpu)) {
+		pmc->counter = val & pmc_bitmask(pmc);
+		return;
+	}
+
 	/*
 	 * Drop any unconsumed accumulated counts, the WRMSR is a write, not a
 	 * read-modify-write.  Adjust the counter value so that its value is
@@ -455,6 +460,28 @@ static int reprogram_counter(struct kvm_pmc *pmc)
 	bool emulate_overflow;
 	u8 fixed_ctr_ctrl;
 
+	if (kvm_mediated_pmu_enabled(pmu_to_vcpu(pmu))) {
+		bool allowed = check_pmu_event_filter(pmc);
+
+		if (pmc_is_gp(pmc)) {
+			if (allowed)
+				pmc->eventsel_hw |= pmc->eventsel &
+						    ARCH_PERFMON_EVENTSEL_ENABLE;
+			else
+				pmc->eventsel_hw &= ~ARCH_PERFMON_EVENTSEL_ENABLE;
+		} else {
+			int idx = pmc->idx - KVM_FIXED_PMC_BASE_IDX;
+
+			if (allowed)
+				pmu->fixed_ctr_ctrl_hw = pmu->fixed_ctr_ctrl;
+			else
+				pmu->fixed_ctr_ctrl_hw &=
+					~intel_fixed_bits_by_idx(idx, 0xf);
+		}
+
+		return 0;
+	}
+
 	emulate_overflow = pmc_pause_counter(pmc);
 
 	if (!pmc_event_is_allowed(pmc))
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index 509c995b7871..6289f523d893 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -113,6 +113,9 @@ static inline u64 pmc_read_counter(struct kvm_pmc *pmc)
 {
 	u64 counter, enabled, running;
 
+	if (kvm_mediated_pmu_enabled(pmc->vcpu))
+		return pmc->counter & pmc_bitmask(pmc);
+
 	counter = pmc->counter + pmc->emulated_counter;
 
 	if (pmc->perf_event && !pmc->is_paused)
-- 
2.49.0.395.g12beb8f557-goog