KVM: x86: Allow marking an exception as reinjected

This patch adds logic to kvm/x86 which allows to mark an
injected exception as reinjected. This allows to remove an
ugly hack from svm_complete_interrupts that prevented
exceptions from being reinjected at all in the nested case.
The hack was necessary because an reinjected exception into
the nested guest could cause a nested vmexit emulation. But
reinjected exceptions must not intercept. The downside of
the hack is that a exception that in injected could get
lost.
This patch fixes the problem and puts the code for it into
generic x86 files because. Nested-VMX will likely have the
same problem and could reuse the code.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -312,6 +312,7 @@ struct kvm_vcpu_arch {
 	struct kvm_queued_exception {
 		bool pending;
 		bool has_error_code;
+		bool reinject;
 		u8 nr;
 		u32 error_code;
 	} exception;
@@ -514,7 +515,8 @@ struct kvm_x86_ops {
 	void (*set_irq)(struct kvm_vcpu *vcpu);
 	void (*set_nmi)(struct kvm_vcpu *vcpu);
 	void (*queue_exception)(struct kvm_vcpu *vcpu, unsigned nr,
-				bool has_error_code, u32 error_code);
+				bool has_error_code, u32 error_code,
+				bool reinject);
 	int (*interrupt_allowed)(struct kvm_vcpu *vcpu);
 	int (*nmi_allowed)(struct kvm_vcpu *vcpu);
 	bool (*get_nmi_mask)(struct kvm_vcpu *vcpu);
@@ -617,6 +619,8 @@ void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
 
 void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr);
 void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
+void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr);
+void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code);
 void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long cr2,
 			   u32 error_code);
 bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl);

arch/x86/kvm/svm.c

@@ -338,7 +338,8 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 }
 
 static void svm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
-				bool has_error_code, u32 error_code)
+				bool has_error_code, u32 error_code,
+				bool reinject)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
@@ -346,7 +347,8 @@ static void svm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
 	 * If we are within a nested VM we'd better #VMEXIT and let the guest
 	 * handle the exception
 	 */
-	if (nested_svm_check_exception(svm, nr, has_error_code, error_code))
+	if (!reinject &&
+	    nested_svm_check_exception(svm, nr, has_error_code, error_code))
 		return;
 
 	if (nr == BP_VECTOR && !svm_has(SVM_FEATURE_NRIP)) {
@@ -2918,8 +2920,6 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
 		svm->vcpu.arch.nmi_injected = true;
 		break;
 	case SVM_EXITINTINFO_TYPE_EXEPT:
-		if (is_nested(svm))
-			break;
 		/*
 		 * In case of software exceptions, do not reinject the vector,
 		 * but re-execute the instruction instead. Rewind RIP first
@@ -2935,10 +2935,10 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
 		}
 		if (exitintinfo & SVM_EXITINTINFO_VALID_ERR) {
 			u32 err = svm->vmcb->control.exit_int_info_err;
-			kvm_queue_exception_e(&svm->vcpu, vector, err);
+			kvm_requeue_exception_e(&svm->vcpu, vector, err);
 
 		} else
-			kvm_queue_exception(&svm->vcpu, vector);
+			kvm_requeue_exception(&svm->vcpu, vector);
 		break;
 	case SVM_EXITINTINFO_TYPE_INTR:
 		kvm_queue_interrupt(&svm->vcpu, vector, false);

arch/x86/kvm/vmx.c

@@ -919,7 +919,8 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 }
 
 static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
-				bool has_error_code, u32 error_code)
+				bool has_error_code, u32 error_code,
+				bool reinject)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	u32 intr_info = nr | INTR_INFO_VALID_MASK;

arch/x86/kvm/x86.c

@@ -265,7 +265,8 @@ static int exception_class(int vector)
 }
 
 static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
-		unsigned nr, bool has_error, u32 error_code)
+		unsigned nr, bool has_error, u32 error_code,
+		bool reinject)
 {
 	u32 prev_nr;
 	int class1, class2;
@@ -276,6 +277,7 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
 		vcpu->arch.exception.has_error_code = has_error;
 		vcpu->arch.exception.nr = nr;
 		vcpu->arch.exception.error_code = error_code;
+		vcpu->arch.exception.reinject = true;
 		return;
 	}
 
@@ -304,10 +306,16 @@ static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
 
 void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
 {
-	kvm_multiple_exception(vcpu, nr, false, 0);
+	kvm_multiple_exception(vcpu, nr, false, 0, false);
 }
 EXPORT_SYMBOL_GPL(kvm_queue_exception);
 
+void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr)
+{
+	kvm_multiple_exception(vcpu, nr, false, 0, true);
+}
+EXPORT_SYMBOL_GPL(kvm_requeue_exception);
+
 void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
 			   u32 error_code)
 {
@@ -324,10 +332,16 @@ EXPORT_SYMBOL_GPL(kvm_inject_nmi);
 
 void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
 {
-	kvm_multiple_exception(vcpu, nr, true, error_code);
+	kvm_multiple_exception(vcpu, nr, true, error_code, false);
 }
 EXPORT_SYMBOL_GPL(kvm_queue_exception_e);
 
+void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
+{
+	kvm_multiple_exception(vcpu, nr, true, error_code, true);
+}
+EXPORT_SYMBOL_GPL(kvm_requeue_exception_e);
+
 /*
  * Checks if cpl <= required_cpl; if true, return true.  Otherwise queue
  * a #GP and return false.
@@ -4408,7 +4422,8 @@ static void inject_pending_event(struct kvm_vcpu *vcpu)
 					vcpu->arch.exception.error_code);
 		kvm_x86_ops->queue_exception(vcpu, vcpu->arch.exception.nr,
 					  vcpu->arch.exception.has_error_code,
-					  vcpu->arch.exception.error_code);
+					  vcpu->arch.exception.error_code,
+					  vcpu->arch.exception.reinject);
 		return;
 	}