KVM: X86: implement the logic for spinlock optimization

get_cpl requires vcpu_load, so we must cache the result (whether the
vcpu was preempted when its cpl=0) in kvm_vcpu_arch.

Signed-off-by: Longpeng(Mike) <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: Longpeng(Mike)

arch/x86/include/asm/kvm_host.h

@@ -688,6 +688,9 @@ struct kvm_vcpu_arch {
 
 	/* GPA available (AMD only) */
 	bool gpa_available;
+
+	/* be preempted when it's in kernel-mode(cpl=0) */
+	bool preempted_in_kernel;
 };
 
 struct kvm_lpage_info {

arch/x86/kvm/hyperv.c

@@ -1274,7 +1274,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 
 	switch (code) {
 	case HVCALL_NOTIFY_LONG_SPIN_WAIT:
-		kvm_vcpu_on_spin(vcpu, false);
+		kvm_vcpu_on_spin(vcpu, true);
 		break;
 	case HVCALL_POST_MESSAGE:
 	case HVCALL_SIGNAL_EVENT:

arch/x86/kvm/svm.c

@@ -3749,7 +3749,10 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
 
 static int pause_interception(struct vcpu_svm *svm)
 {
-	kvm_vcpu_on_spin(&svm->vcpu, false);
+	struct kvm_vcpu *vcpu = &svm->vcpu;
+	bool in_kernel = (svm_get_cpl(vcpu) == 0);
+
+	kvm_vcpu_on_spin(vcpu, in_kernel);
 	return 1;
 }
 

arch/x86/kvm/vmx.c

@@ -6781,7 +6781,13 @@ static int handle_pause(struct kvm_vcpu *vcpu)
 	if (ple_gap)
 		grow_ple_window(vcpu);
 
-	kvm_vcpu_on_spin(vcpu, false);
+	/*
+	 * Intel sdm vol3 ch-25.1.3 says: The "PAUSE-loop exiting"
+	 * VM-execution control is ignored if CPL > 0. OTOH, KVM
+	 * never set PAUSE_EXITING and just set PLE if supported,
+	 * so the vcpu must be CPL=0 if it gets a PAUSE exit.
+	 */
+	kvm_vcpu_on_spin(vcpu, true);
 	return kvm_skip_emulated_instruction(vcpu);
 }
 

arch/x86/kvm/x86.c

@@ -2873,6 +2873,10 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	int idx;
+
+	if (vcpu->preempted)
+		vcpu->arch.preempted_in_kernel = !kvm_x86_ops->get_cpl(vcpu);
+
 	/*
 	 * Disable page faults because we're in atomic context here.
 	 * kvm_write_guest_offset_cached() would call might_fault()
@@ -7985,6 +7989,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	kvm_pmu_init(vcpu);
 
 	vcpu->arch.pending_external_vector = -1;
+	vcpu->arch.preempted_in_kernel = false;
 
 	kvm_hv_vcpu_init(vcpu);
 
@@ -8434,7 +8439,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 
 bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
 {
-	return false;
+	return vcpu->arch.preempted_in_kernel;
 }
 
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)