1 files changed, 40 insertions, 5 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7dda9c4ee485..1a854ce6025e 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -189,6 +189,7 @@ struct vcpu_svm {
 	struct nested_state nested;
 
 	bool nmi_singlestep;
+	u64 nmi_singlestep_guest_rflags;
 
 	unsigned int3_injected;
 	unsigned long int3_rip;
@@ -966,9 +967,13 @@ static void svm_disable_lbrv(struct vcpu_svm *svm)
 static void disable_nmi_singlestep(struct vcpu_svm *svm)
 {
 	svm->nmi_singlestep = false;
-	if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))
-		svm->vmcb->save.rflags &=
-			~(X86_EFLAGS_TF | X86_EFLAGS_RF);
+	if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP)) {
+		/* Clear our flags if they were not set by the guest */
+		if (!(svm->nmi_singlestep_guest_rflags & X86_EFLAGS_TF))
+			svm->vmcb->save.rflags &= ~X86_EFLAGS_TF;
+		if (!(svm->nmi_singlestep_guest_rflags & X86_EFLAGS_RF))
+			svm->vmcb->save.rflags &= ~X86_EFLAGS_RF;
+	}
 }
 
 /* Note:
@@ -2538,6 +2543,31 @@ static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
 	return (value & mask) ? NESTED_EXIT_DONE : NESTED_EXIT_HOST;
 }
 
+/* DB exceptions for our internal use must not cause vmexit */
+static int nested_svm_intercept_db(struct vcpu_svm *svm)
+{
+	unsigned long dr6;
+
+	/* if we're not singlestepping, it's not ours */
+	if (!svm->nmi_singlestep)
+		return NESTED_EXIT_DONE;
+
+	/* if it's not a singlestep exception, it's not ours */
+	if (kvm_get_dr(&svm->vcpu, 6, &dr6))
+		return NESTED_EXIT_DONE;
+	if (!(dr6 & DR6_BS))
+		return NESTED_EXIT_DONE;
+
+	/* if the guest is singlestepping, it should get the vmexit */
+	if (svm->nmi_singlestep_guest_rflags & X86_EFLAGS_TF) {
+		disable_nmi_singlestep(svm);
+		return NESTED_EXIT_DONE;
+	}
+
+	/* it's ours, the nested hypervisor must not see this one */
+	return NESTED_EXIT_HOST;
+}
+
 static int nested_svm_exit_special(struct vcpu_svm *svm)
 {
 	u32 exit_code = svm->vmcb->control.exit_code;
@@ -2593,8 +2623,12 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
 	}
 	case SVM_EXIT_EXCP_BASE ... SVM_EXIT_EXCP_BASE + 0x1f: {
 		u32 excp_bits = 1 << (exit_code - SVM_EXIT_EXCP_BASE);
-		if (svm->nested.intercept_exceptions & excp_bits)
-			vmexit = NESTED_EXIT_DONE;
+		if (svm->nested.intercept_exceptions & excp_bits) {
+			if (exit_code == SVM_EXIT_EXCP_BASE + DB_VECTOR)
+				vmexit = nested_svm_intercept_db(svm);
+			else
+				vmexit = NESTED_EXIT_DONE;
+		}
 		/* async page fault always cause vmexit */
 		else if ((exit_code == SVM_EXIT_EXCP_BASE + PF_VECTOR) &&
 			 svm->apf_reason != 0)
@@ -4635,6 +4669,7 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
 	 * Something prevents NMI from been injected. Single step over possible
 	 * problem (IRET or exception injection or interrupt shadow)
 	 */
+	svm->nmi_singlestep_guest_rflags = svm_get_rflags(vcpu);
 	svm->nmi_singlestep = true;
 	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
 }