[PATCH v3 9/9] KVM: VMX: Only tell perf to enable PEBS counters for fully enabled PMCs

[Sean Christopherson]

When passing the guest's requested PEBS_ENABLE (or rather, KVM's version
of PEBS_ENABLE on behalf of the guest), omit counters that are locally
disable and/or don't have a perf event (due to contention), in addition to
omitting counters that are cross-mapped in the host.

In practice, this should be a nop as perf will already have disabled the
associated counter, i.e. cpuc->pebs_enabled should have been cleared, but
paranoia is cheap, and the existing code _looks_ wrong.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/pmu_intel.c | 30 ++++++++++++++++--------------
 arch/x86/kvm/vmx/vmx.c       | 11 +----------
 arch/x86/kvm/vmx/vmx.h       | 15 ++++++++++++++-
 3 files changed, 31 insertions(+), 25 deletions(-)

diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c
index 659fe097b904..1e420c8bca9d 100644
--- a/arch/x86/kvm/vmx/pmu_intel.c
+++ b/arch/x86/kvm/vmx/pmu_intel.c
@@ -736,34 +736,36 @@ static void intel_pmu_cleanup(struct kvm_vcpu *vcpu)
 		intel_pmu_release_guest_lbr_event(vcpu);
 }
 
-u64 intel_pmu_get_cross_mapped_mask(struct kvm_pmu *pmu)
+u64 __intel_pmu_compute_pebs_enable(struct kvm_pmu *pmu)
 {
-	u64 host_cross_mapped_mask;
+	u64 guest_pebs_enable = pmu->pebs_enable & pmu->global_ctrl;
+	u64 pebs_enable = 0;
 	struct kvm_pmc *pmc;
 	int bit, hw_idx;
 
 	/*
-	 * Provide a mask of counters that are cross-mapped between the guest
-	 * and the host, i.e. where a guest PMC is mapped to a host PMC with a
-	 * different index.  PEBS records hold a PERF_GLOBAL_STATUS snapshot,
-	 * and so PEBS-enabled counters need to hold the correct index so as
-	 * not to confuse the guest.
+	 * Omit counters that are locally disabled, don't have a perf event, or
+	 * ended up with a perf event that is using a different counter than
+	 * the guest, i.e. where the guest PMC is different than the host PMC
+	 * being used on behalf of the guest.  PEBS records include
+	 * PERF_GLOBAL_STATUS, and so using a counter with a different index
+	 * means the guest will see overflow status for the wrong counter(s).
 	 */
-	host_cross_mapped_mask = 0;
-
-	kvm_for_each_pmc(pmu, pmc, bit, (unsigned long *)&pmu->global_ctrl) {
+	kvm_for_each_pmc(pmu, pmc, bit, (unsigned long *)&guest_pebs_enable) {
 		if (!pmc_is_locally_enabled(pmc) || !pmc->perf_event)
 			continue;
 
 		/*
-		 * A negative index indicates the event isn't mapped to a
+		 * Note, a negative index indicates the event isn't mapped to a
 		 * physical counter in the host, e.g. due to contention.
 		 */
 		hw_idx = pmc->perf_event->hw.idx;
-		if (hw_idx != pmc->idx && hw_idx > -1)
-			host_cross_mapped_mask |= BIT_ULL(hw_idx);
+		if (hw_idx != pmc->idx)
+			continue;
+
+		pebs_enable |= BIT_ULL(pmc->idx);
 	}
-	return host_cross_mapped_mask;
+	return pebs_enable;
 }
 
 static bool intel_pmu_is_mediated_pmu_supported(struct x86_pmu_capability *host_pmu)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index fbe3ce5f5a51..31675e5cf563 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7314,20 +7314,11 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
 		return;
 
 	struct x86_guest_pebs guest_pebs = {
-		.enable = pmu->pebs_enable,
+		.enable = intel_pmu_compute_pebs_enable(pmu),
 		.ds_area = pmu->ds_area,
 		.data_cfg = pmu->pebs_data_cfg,
 	};
 
-	/*
-	 * Disable counters where the guest PMC is different than the host PMC
-	 * being used on behalf of the guest, as the PEBS record includes
-	 * PERF_GLOBAL_STATUS, i.e. the guest will see overflow status for the
-	 * wrong counter(s).
-	 */
-	if (guest_pebs.enable & pmu->global_ctrl)
-		guest_pebs.enable &= ~intel_pmu_get_cross_mapped_mask(pmu);
-
 	/* Note, nr_msrs may be garbage if perf_guest_get_msrs() returns NULL. */
 	msrs = perf_guest_get_msrs(&nr_msrs, &guest_pebs);
 	if (!msrs)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 0c4563472940..b055731efd2d 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -659,7 +659,20 @@ static __always_inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)
 	return container_of(vcpu, struct vcpu_vmx, vcpu);
 }
 
-u64 intel_pmu_get_cross_mapped_mask(struct kvm_pmu *pmu);
+u64 __intel_pmu_compute_pebs_enable(struct kvm_pmu *pmu);
+
+static inline u64 intel_pmu_compute_pebs_enable(struct kvm_pmu *pmu)
+{
+	/*
+	 * Avoid the function call overhead in the common case that the guest
+	 * isn't using PEBS.
+	 */
+	if (!(pmu->pebs_enable & pmu->global_ctrl))
+		return 0;
+
+	return __intel_pmu_compute_pebs_enable(pmu);
+}
+
 int intel_pmu_create_guest_lbr_event(struct kvm_vcpu *vcpu);
 void vmx_passthrough_lbr_msrs(struct kvm_vcpu *vcpu);
 
-- 
2.54.0.563.g4f69b47b94-goog