Merge tag 'kvm-x86-pmu-6.8' of https://github.com/kvm-x86/linux into HEAD

KVM x86 PMU changes for 6.8:

 - Fix a variety of bugs where KVM fail to stop/reset counters and other state
   prior to refreshing the vPMU model.

 - Fix a double-overflow PMU bug by tracking emulated counter events using a
   dedicated field instead of snapshotting the "previous" counter.  If the
   hardware PMC count triggers overflow that is recognized in the same VM-Exit
   that KVM manually bumps an event count, KVM would pend PMIs for both the
   hardware-triggered overflow and for KVM-triggered overflow.

2 files changed, 17 insertions, 2 deletions

diff --git a/arch/x86/include/asm/kvm-x86-pmu-ops.h b/arch/x86/include/asm/kvm-x86-pmu-ops.h
index 6c98f4bb4228..058bc636356a 100644
--- a/arch/x86/include/asm/kvm-x86-pmu-ops.h
+++ b/arch/x86/include/asm/kvm-x86-pmu-ops.h
@@ -22,7 +22,7 @@ KVM_X86_PMU_OP(get_msr)
 KVM_X86_PMU_OP(set_msr)
 KVM_X86_PMU_OP(refresh)
 KVM_X86_PMU_OP(init)
-KVM_X86_PMU_OP(reset)
+KVM_X86_PMU_OP_OPTIONAL(reset)
 KVM_X86_PMU_OP_OPTIONAL(deliver_pmi)
 KVM_X86_PMU_OP_OPTIONAL(cleanup)
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index b093c2191cd3..c17e38ac8b7a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -500,8 +500,23 @@ struct kvm_pmc {
 	u8 idx;
 	bool is_paused;
 	bool intr;
+	/*
+	 * Base value of the PMC counter, relative to the *consumed* count in
+	 * the associated perf_event.  This value includes counter updates from
+	 * the perf_event and emulated_count since the last time the counter
+	 * was reprogrammed, but it is *not* the current value as seen by the
+	 * guest or userspace.
+	 *
+	 * The count is relative to the associated perf_event so that KVM
+	 * doesn't need to reprogram the perf_event every time the guest writes
+	 * to the counter.
+	 */
 	u64 counter;
-	u64 prev_counter;
+	/*
+	 * PMC events triggered by KVM emulation that haven't been fully
+	 * processed, i.e. haven't undergone overflow detection.
+	 */
+	u64 emulated_counter;
 	u64 eventsel;
 	struct perf_event *perf_event;
 	struct kvm_vcpu *vcpu;