Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm/x86 fixes from Paolo Bonzini:

 - zero all padding for KVM_GET_DEBUGREGS

 - fix rST warning

 - disable vPMU support on hybrid CPUs

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  kvm: initialize all of the kvm_debugregs structure before sending it to userspace
  perf/x86: Refuse to export capabilities for hybrid PMUs
  KVM: x86/pmu: Disable vPMU support on hybrid CPUs (host PMUs)
  Documentation/hw-vuln: Fix rST warning

Author: torvalds

Documentation/admin-guide/hw-vuln/cross-thread-rsb.rst

@@ -88,5 +88,4 @@ capability to override those interceptions, but since this is not common, the
 mitigation that covers this path is not enabled by default.
 
 The mitigation for the KVM_CAP_X86_DISABLE_EXITS capability can be turned on
-using the boolean module parameter mitigate_smt_rsb, e.g.:
-        kvm.mitigate_smt_rsb=1
+using the boolean module parameter mitigate_smt_rsb, e.g. ``kvm.mitigate_smt_rsb=1``.

arch/x86/events/core.c

@@ -2974,17 +2974,19 @@ unsigned long perf_misc_flags(struct pt_regs *regs)
 
 void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap)
 {
-	if (!x86_pmu_initialized()) {
+	/* This API doesn't currently support enumerating hybrid PMUs. */
+	if (WARN_ON_ONCE(cpu_feature_enabled(X86_FEATURE_HYBRID_CPU)) ||
+	    !x86_pmu_initialized()) {
 		memset(cap, 0, sizeof(*cap));
 		return;
 	}
 
-	cap->version		= x86_pmu.version;
 	/*
-	 * KVM doesn't support the hybrid PMU yet.
-	 * Return the common value in global x86_pmu,
-	 * which available for all cores.
+	 * Note, hybrid CPU models get tracked as having hybrid PMUs even when
+	 * all E-cores are disabled via BIOS.  When E-cores are disabled, the
+	 * base PMU holds the correct number of counters for P-cores.
 	 */
+	cap->version		= x86_pmu.version;
 	cap->num_counters_gp	= x86_pmu.num_counters;
 	cap->num_counters_fixed	= x86_pmu.num_counters_fixed;
 	cap->bit_width_gp	= x86_pmu.cntval_bits;

arch/x86/kvm/pmu.h

@@ -165,15 +165,27 @@ static inline void kvm_init_pmu_capability(void)
 {
 	bool is_intel = boot_cpu_data.x86_vendor == X86_VENDOR_INTEL;
 
-	perf_get_x86_pmu_capability(&kvm_pmu_cap);
-
-	 /*
-	  * For Intel, only support guest architectural pmu
-	  * on a host with architectural pmu.
-	  */
-	if ((is_intel && !kvm_pmu_cap.version) || !kvm_pmu_cap.num_counters_gp)
+	/*
+	 * Hybrid PMUs don't play nice with virtualization without careful
+	 * configuration by userspace, and KVM's APIs for reporting supported
+	 * vPMU features do not account for hybrid PMUs.  Disable vPMU support
+	 * for hybrid PMUs until KVM gains a way to let userspace opt-in.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
 		enable_pmu = false;
 
+	if (enable_pmu) {
+		perf_get_x86_pmu_capability(&kvm_pmu_cap);
+
+		/*
+		 * For Intel, only support guest architectural pmu
+		 * on a host with architectural pmu.
+		 */
+		if ((is_intel && !kvm_pmu_cap.version) ||
+		    !kvm_pmu_cap.num_counters_gp)
+			enable_pmu = false;
+	}
+
 	if (!enable_pmu) {
 		memset(&kvm_pmu_cap, 0, sizeof(kvm_pmu_cap));
 		return;

arch/x86/kvm/x86.c

@@ -5263,12 +5263,11 @@ static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 {
 	unsigned long val;
 
+	memset(dbgregs, 0, sizeof(*dbgregs));
 	memcpy(dbgregs->db, vcpu->arch.db, sizeof(vcpu->arch.db));
 	kvm_get_dr(vcpu, 6, &val);
 	dbgregs->dr6 = val;
 	dbgregs->dr7 = vcpu->arch.dr7;
-	dbgregs->flags = 0;
-	memset(&dbgregs->reserved, 0, sizeof(dbgregs->reserved));
 }
 
 static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,