KVM: X86: Provide a capability to disable PAUSE intercepts

Allow to disable pause loop exit/pause filtering on a per VM basis.

If some VMs have dedicated host CPUs, they won't be negatively affected
due to needlessly intercepted PAUSE instructions.

Thanks to Jan H. Schönherr's initial patch.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -813,6 +813,7 @@ struct kvm_arch {
 
 	bool mwait_in_guest;
 	bool hlt_in_guest;
+	bool pause_in_guest;
 
 	bool ept_identity_pagetable_done;
 	gpa_t ept_identity_map_addr;

arch/x86/kvm/svm.c

@@ -1460,7 +1460,8 @@ static void init_vmcb(struct vcpu_svm *svm)
 	svm->nested.vmcb = 0;
 	svm->vcpu.arch.hflags = 0;
 
-	if (boot_cpu_has(X86_FEATURE_PAUSEFILTER)) {
+	if (boot_cpu_has(X86_FEATURE_PAUSEFILTER) &&
+	    !kvm_pause_in_guest(svm->vcpu.kvm)) {
 		control->pause_filter_count = 3000;
 		set_intercept(svm, INTERCEPT_PAUSE);
 	}

arch/x86/kvm/vmx.c

@@ -5595,7 +5595,7 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
 	}
 	if (!enable_unrestricted_guest)
 		exec_control &= ~SECONDARY_EXEC_UNRESTRICTED_GUEST;
-	if (!ple_gap)
+	if (kvm_pause_in_guest(vmx->vcpu.kvm))
 		exec_control &= ~SECONDARY_EXEC_PAUSE_LOOP_EXITING;
 	if (!kvm_vcpu_apicv_active(vcpu))
 		exec_control &= ~(SECONDARY_EXEC_APIC_REGISTER_VIRT |
@@ -5758,7 +5758,7 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
 		vmcs_write64(POSTED_INTR_DESC_ADDR, __pa((&vmx->pi_desc)));
 	}
 
-	if (ple_gap) {
+	if (!kvm_pause_in_guest(vmx->vcpu.kvm)) {
 		vmcs_write32(PLE_GAP, ple_gap);
 		vmx->ple_window = ple_window;
 		vmx->ple_window_dirty = true;
@@ -7207,7 +7207,7 @@ static __exit void hardware_unsetup(void)
  */
 static int handle_pause(struct kvm_vcpu *vcpu)
 {
-	if (ple_gap)
+	if (!kvm_pause_in_guest(vcpu->kvm))
 		grow_ple_window(vcpu);
 
 	/*
@@ -9903,6 +9903,13 @@ free_vcpu:
 	return ERR_PTR(err);
 }
 
+static int vmx_vm_init(struct kvm *kvm)
+{
+	if (!ple_gap)
+		kvm->arch.pause_in_guest = true;
+	return 0;
+}
+
 static void __init vmx_check_processor_compat(void *rtn)
 {
 	struct vmcs_config vmcs_conf;
@@ -12052,7 +12059,7 @@ static void vmx_cancel_hv_timer(struct kvm_vcpu *vcpu)
 
 static void vmx_sched_in(struct kvm_vcpu *vcpu, int cpu)
 {
-	if (ple_gap)
+	if (!kvm_pause_in_guest(vcpu->kvm))
 		shrink_ple_window(vcpu);
 }
 
@@ -12412,6 +12419,8 @@ static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
 	.cpu_has_accelerated_tpr = report_flexpriority,
 	.cpu_has_high_real_mode_segbase = vmx_has_high_real_mode_segbase,
 
+	.vm_init = vmx_vm_init,
+
 	.vcpu_create = vmx_create_vcpu,
 	.vcpu_free = vmx_free_vcpu,
 	.vcpu_reset = vmx_vcpu_reset,

arch/x86/kvm/x86.c

@@ -2878,7 +2878,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = KVM_CLOCK_TSC_STABLE;
 		break;
 	case KVM_CAP_X86_DISABLE_EXITS:
-		r |=  KVM_X86_DISABLE_EXITS_HTL;
+		r |=  KVM_X86_DISABLE_EXITS_HTL | KVM_X86_DISABLE_EXITS_PAUSE;
 		if(kvm_can_mwait_in_guest())
 			r |= KVM_X86_DISABLE_EXITS_MWAIT;
 		break;
@@ -4235,6 +4235,8 @@ split_irqchip_unlock:
 			kvm->arch.mwait_in_guest = true;
 		if (cap->args[0] & KVM_X86_DISABLE_EXITS_HTL)
 			kvm->arch.hlt_in_guest = true;
+		if (cap->args[0] & KVM_X86_DISABLE_EXITS_PAUSE)
+			kvm->arch.pause_in_guest = true;
 		r = 0;
 		break;
 	default:

arch/x86/kvm/x86.h

@@ -266,8 +266,10 @@ static inline u64 nsec_to_cycles(struct kvm_vcpu *vcpu, u64 nsec)
 
 #define KVM_X86_DISABLE_EXITS_MWAIT          (1 << 0)
 #define KVM_X86_DISABLE_EXITS_HTL            (1 << 1)
+#define KVM_X86_DISABLE_EXITS_PAUSE          (1 << 2)
 #define KVM_X86_DISABLE_VALID_EXITS          (KVM_X86_DISABLE_EXITS_MWAIT | \
-                                              KVM_X86_DISABLE_EXITS_HTL)
+                                              KVM_X86_DISABLE_EXITS_HTL | \
+                                              KVM_X86_DISABLE_EXITS_PAUSE)
 
 static inline bool kvm_mwait_in_guest(struct kvm *kvm)
 {
@@ -279,4 +281,9 @@ static inline bool kvm_hlt_in_guest(struct kvm *kvm)
 	return kvm->arch.hlt_in_guest;
 }
 
+static inline bool kvm_pause_in_guest(struct kvm *kvm)
+{
+	return kvm->arch.pause_in_guest;
+}
+
 #endif