KVM: x86: nSVM: implement nested vGIF

In case L1 enables vGIF for L2, the L2 cannot affect L1's GIF, regardless
of STGI/CLGI intercepts, and since VM entry enables GIF, this means
that L1's GIF is always 1 while L2 is running.

Thus in this case leave L1's vGIF in vmcb01, while letting L2
control the vGIF thus implementing nested vGIF.

Also allow KVM to toggle L1's GIF during nested entry/exit
by always using vmcb01.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220322174050.241850-5-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -439,6 +439,10 @@ void nested_sync_control_from_vmcb02(struct vcpu_svm *svm)
 		 */
 		mask &= ~V_IRQ_MASK;
 	}
+
+	if (nested_vgif_enabled(svm))
+		mask |= V_GIF_MASK;
+
 	svm->nested.ctl.int_ctl        &= ~mask;
 	svm->nested.ctl.int_ctl        |= svm->vmcb->control.int_ctl & mask;
 }
@@ -604,10 +608,8 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 
 static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 {
-	const u32 int_ctl_vmcb01_bits =
-		V_INTR_MASKING_MASK | V_GIF_MASK | V_GIF_ENABLE_MASK;
-
-	const u32 int_ctl_vmcb12_bits = V_TPR_MASK | V_IRQ_INJECTION_BITS_MASK;
+	u32 int_ctl_vmcb01_bits = V_INTR_MASKING_MASK;
+	u32 int_ctl_vmcb12_bits = V_TPR_MASK | V_IRQ_INJECTION_BITS_MASK;
 
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 	struct vmcb *vmcb01 = svm->vmcb01.ptr;
@@ -624,6 +626,11 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm)
 	 */
 	WARN_ON(kvm_apicv_activated(svm->vcpu.kvm));
 
+	if (svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK))
+		int_ctl_vmcb12_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
+	else
+		int_ctl_vmcb01_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
+
 	/* Copied from vmcb01.  msrpm_base can be overwritten later.  */
 	vmcb02->control.nested_ctl = vmcb01->control.nested_ctl;
 	vmcb02->control.iopm_base_pa = vmcb01->control.iopm_base_pa;

arch/x86/kvm/svm/svm.c

@@ -4028,6 +4028,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	svm->pause_threshold_enabled = kvm_cpu_cap_has(X86_FEATURE_PFTHRESHOLD) &&
 			guest_cpuid_has(vcpu, X86_FEATURE_PFTHRESHOLD);
 
+	svm->vgif_enabled = vgif && guest_cpuid_has(vcpu, X86_FEATURE_VGIF);
+
 	svm_recalc_instruction_intercepts(vcpu, svm);
 
 	/* For sev guests, the memory encryption bit is not reserved in CR3.  */
@@ -4787,6 +4789,9 @@ static __init void svm_set_cpu_caps(void)
 		if (boot_cpu_has(X86_FEATURE_PFTHRESHOLD))
 			kvm_cpu_cap_set(X86_FEATURE_PFTHRESHOLD);
 
+		if (vgif)
+			kvm_cpu_cap_set(X86_FEATURE_VGIF);
+
 		/* Nested VM can receive #VMEXIT instead of triggering #GP */
 		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}

arch/x86/kvm/svm/svm.h

@@ -239,6 +239,7 @@ struct vcpu_svm {
 	bool lbrv_enabled                 : 1;
 	bool pause_filter_enabled         : 1;
 	bool pause_threshold_enabled      : 1;
+	bool vgif_enabled                 : 1;
 
 	u32 ldr_reg;
 	u32 dfr_reg;
@@ -457,26 +458,48 @@ static inline bool svm_is_intercept(struct vcpu_svm *svm, int bit)
 	return vmcb_is_intercept(&svm->vmcb->control, bit);
 }
 
+static inline bool nested_vgif_enabled(struct vcpu_svm *svm)
+{
+	return svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK);
+}
+
+static inline struct vmcb *get_vgif_vmcb(struct vcpu_svm *svm)
+{
+	if (!vgif)
+		return NULL;
+
+	if (is_guest_mode(&svm->vcpu) && !nested_vgif_enabled(svm))
+		return svm->nested.vmcb02.ptr;
+	else
+		return svm->vmcb01.ptr;
+}
+
 static inline void enable_gif(struct vcpu_svm *svm)
 {
-	if (vgif)
-		svm->vmcb->control.int_ctl |= V_GIF_MASK;
+	struct vmcb *vmcb = get_vgif_vmcb(svm);
+
+	if (vmcb)
+		vmcb->control.int_ctl |= V_GIF_MASK;
 	else
 		svm->vcpu.arch.hflags |= HF_GIF_MASK;
 }
 
 static inline void disable_gif(struct vcpu_svm *svm)
 {
-	if (vgif)
-		svm->vmcb->control.int_ctl &= ~V_GIF_MASK;
+	struct vmcb *vmcb = get_vgif_vmcb(svm);
+
+	if (vmcb)
+		vmcb->control.int_ctl &= ~V_GIF_MASK;
 	else
 		svm->vcpu.arch.hflags &= ~HF_GIF_MASK;
 }
 
 static inline bool gif_set(struct vcpu_svm *svm)
 {
-	if (vgif)
-		return !!(svm->vmcb->control.int_ctl & V_GIF_MASK);
+	struct vmcb *vmcb = get_vgif_vmcb(svm);
+
+	if (vmcb)
+		return !!(vmcb->control.int_ctl & V_GIF_MASK);
 	else
 		return !!(svm->vcpu.arch.hflags & HF_GIF_MASK);
 }