KVM: SVM: Re-inject INTn instead of retrying the insn on "failure"

Re-inject INTn software interrupts instead of retrying the instruction if
the CPU encountered an intercepted exception while vectoring the INTn,
e.g. if KVM intercepted a #PF when utilizing shadow paging.  Retrying the
instruction is architecturally wrong e.g. will result in a spurious #DB
if there's a code breakpoint on the INT3/O, and lack of re-injection also
breaks nested virtualization, e.g. if L1 injects a software interrupt and
vectoring the injected interrupt encounters an exception that is
intercepted by L0 but not L1.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Message-Id: <1654ad502f860948e4f2d57b8bd881d67301f785.1651440202.git.maciej.szmigiero@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/nested.c

@@ -617,10 +617,9 @@ static inline bool is_evtinj_soft(u32 evtinj)
 	if (!(evtinj & SVM_EVTINJ_VALID))
 		return false;
 
-	/*
-	 * Intentionally return false for SOFT events, SVM doesn't yet support
-	 * re-injecting soft interrupts.
-	 */
+	if (type == SVM_EVTINJ_TYPE_SOFT)
+		return true;
+
 	return type == SVM_EVTINJ_TYPE_EXEPT && kvm_exception_is_soft(vector);
 }
 

arch/x86/kvm/svm/svm.c

@@ -3438,12 +3438,22 @@ static void svm_inject_nmi(struct kvm_vcpu *vcpu)
 static void svm_inject_irq(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	u32 type;
+
+	if (vcpu->arch.interrupt.soft) {
+		if (svm_update_soft_interrupt_rip(vcpu))
+			return;
+
+		type = SVM_EVTINJ_TYPE_SOFT;
+	} else {
+		type = SVM_EVTINJ_TYPE_INTR;
+	}
 
 	trace_kvm_inj_virq(vcpu->arch.interrupt.nr);
 	++vcpu->stat.irq_injections;
 
 	svm->vmcb->control.event_inj = vcpu->arch.interrupt.nr |
-		SVM_EVTINJ_VALID | SVM_EVTINJ_TYPE_INTR;
+				       SVM_EVTINJ_VALID | type;
 }
 
 void svm_complete_interrupt_delivery(struct kvm_vcpu *vcpu, int delivery_mode,
@@ -3723,6 +3733,8 @@ static inline void sync_lapic_to_cr8(struct kvm_vcpu *vcpu)
 static void svm_complete_soft_interrupt(struct kvm_vcpu *vcpu, u8 vector,
 					int type)
 {
+	bool is_exception = (type == SVM_EXITINTINFO_TYPE_EXEPT);
+	bool is_soft = (type == SVM_EXITINTINFO_TYPE_SOFT);
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	/*
@@ -3734,8 +3746,7 @@ static void svm_complete_soft_interrupt(struct kvm_vcpu *vcpu, u8 vector,
 	 * the same event, i.e. if the event is a soft exception/interrupt,
 	 * otherwise next_rip is unused on VMRUN.
 	 */
-	if (nrips && type == SVM_EXITINTINFO_TYPE_EXEPT &&
-	    kvm_exception_is_soft(vector) &&
+	if (nrips && (is_soft || (is_exception && kvm_exception_is_soft(vector))) &&
 	    kvm_is_linear_rip(vcpu, svm->soft_int_old_rip + svm->soft_int_csbase))
 		svm->vmcb->control.next_rip = svm->soft_int_next_rip;
 	/*
@@ -3746,7 +3757,7 @@ static void svm_complete_soft_interrupt(struct kvm_vcpu *vcpu, u8 vector,
 	 * hit a #NP in the guest, and the #NP encountered a #PF, the #NP will
 	 * be the reported vectored event, but RIP still needs to be unwound.
 	 */
-	else if (!nrips && type == SVM_EXITINTINFO_TYPE_EXEPT &&
+	else if (!nrips && (is_soft || is_exception) &&
 		 kvm_is_linear_rip(vcpu, svm->soft_int_next_rip + svm->soft_int_csbase))
 		kvm_rip_write(vcpu, svm->soft_int_old_rip);
 }
@@ -3808,9 +3819,13 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
 	case SVM_EXITINTINFO_TYPE_INTR:
 		kvm_queue_interrupt(vcpu, vector, false);
 		break;
+	case SVM_EXITINTINFO_TYPE_SOFT:
+		kvm_queue_interrupt(vcpu, vector, true);
+		break;
 	default:
 		break;
 	}
+
 }
 
 static void svm_cancel_injection(struct kvm_vcpu *vcpu)