[PATCH] KVM: SVM: Re-inject soft interrupts instead of retrying instruction

[Sean Christopherson]

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/svm/svm.c | 101 +++++++++++++++++++++++++++++------------
 arch/x86/kvm/svm/svm.h |   4 +-
 2 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 2c86bd9176c6..c534d00ae194 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -370,6 +370,45 @@ static int svm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+static int svm_update_soft_interrupt_rip(struct kvm_vcpu *vcpu)
+{
+	unsigned long rip, old_rip = kvm_rip_read(vcpu);
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	/*
+	 * Due to architectural shortcomings, the CPU doesn't always provide
+	 * NextRIP, e.g. if KVM intercepted an exception that occurred while
+	 * the CPU was vectoring an INTO/INT3 in the guest.  Temporarily skip
+	 * the instruction even if NextRIP is supported to acquire the next
+	 * RIP so that it can be shoved into the NextRIP field, otherwise
+	 * hardware will fail to advance guest RIP during event injection.
+	 * Drop the exception/interrupt if emulation fails and effectively
+	 * retry the instruction, it's the least awful option.
+	 */
+	if (!svm_skip_emulated_instruction(vcpu))
+		return -EIO;
+
+	rip = kvm_rip_read(vcpu);
+
+	/*
+	 * If NextRIP is supported, rewind RIP and update NextRip.  If NextRip
+	 * isn't supported, keep the result of the skip as the CPU obviously
+	 * won't advance RIP, but stash away the injection information so that
+	 * RIP can be unwound if injection fails.
+	 */
+	if (nrips) {
+		kvm_rip_write(vcpu, old_rip);
+		svm->vmcb->control.next_rip = rip;
+	} else {
+		if (static_cpu_has(X86_FEATURE_NRIPS))
+			svm->vmcb->control.next_rip = rip;
+
+		svm->soft_int_linear_rip = rip + svm->vmcb->save.cs.base;
+		svm->soft_int_injected = rip - old_rip;
+	}
+	return 0;
+}
+
 static void svm_queue_exception(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
@@ -379,21 +418,9 @@ static void svm_queue_exception(struct kvm_vcpu *vcpu)
 
 	kvm_deliver_exception_payload(vcpu);
 
-	if (nr == BP_VECTOR && !nrips) {
-		unsigned long rip, old_rip = kvm_rip_read(vcpu);
-
-		/*
-		 * For guest debugging where we have to reinject #BP if some
-		 * INT3 is guest-owned:
-		 * Emulate nRIP by moving RIP forward. Will fail if injection
-		 * raises a fault that is not intercepted. Still better than
-		 * failing in all cases.
-		 */
-		(void)svm_skip_emulated_instruction(vcpu);
-		rip = kvm_rip_read(vcpu);
-		svm->int3_rip = rip + svm->vmcb->save.cs.base;
-		svm->int3_injected = rip - old_rip;
-	}
+	if (kvm_exception_is_soft(nr) &&
+	    svm_update_soft_interrupt_rip(vcpu))
+		return;
 
 	svm->vmcb->control.event_inj = nr
 		| SVM_EVTINJ_VALID
@@ -3382,14 +3409,24 @@ 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;
 
 	WARN_ON(!gif_set(svm));
 
+	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,
@@ -3672,9 +3709,9 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
 	u8 vector;
 	int type;
 	u32 exitintinfo = svm->vmcb->control.exit_int_info;
-	unsigned int3_injected = svm->int3_injected;
+	unsigned soft_int_injected = svm->soft_int_injected;
 
-	svm->int3_injected = 0;
+	svm->soft_int_injected = 0;
 
 	/*
 	 * If we've made progress since setting HF_IRET_MASK, we've
@@ -3694,6 +3731,18 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
 	if (!(exitintinfo & SVM_EXITINTINFO_VALID))
 		return;
 
+	/*
+	 * If NextRIP isn't enabled, KVM must manually advance RIP prior to
+	 * injecting the soft exception/interrupt.  That advancement needs to
+	 * be unwound if vectoring didn't complete.  Note, the _new_ event may
+	 * not be the injected event, e.g. if KVM injected an INTn, the INTn
+	 * 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.
+	 */
+	if (soft_int_injected &&
+	    kvm_is_linear_rip(vcpu, to_svm(vcpu)->soft_int_linear_rip))
+		kvm_rip_write(vcpu, kvm_rip_read(vcpu) - soft_int_injected);
+
 	kvm_make_request(KVM_REQ_EVENT, vcpu);
 
 	vector = exitintinfo & SVM_EXITINTINFO_VEC_MASK;
@@ -3710,18 +3759,6 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
 		if (vector == X86_TRAP_VC)
 			break;
 
-		/*
-		 * In case of software exceptions, do not reinject the vector,
-		 * but re-execute the instruction instead. Rewind RIP first
-		 * if we emulated INT3 before.
-		 */
-		if (kvm_exception_is_soft(vector)) {
-			if (vector == BP_VECTOR && int3_injected &&
-			    kvm_is_linear_rip(vcpu, svm->int3_rip))
-				kvm_rip_write(vcpu,
-					      kvm_rip_read(vcpu) - int3_injected);
-			break;
-		}
 		if (exitintinfo & SVM_EXITINTINFO_VALID_ERR) {
 			u32 err = svm->vmcb->control.exit_int_info_err;
 			kvm_requeue_exception_e(vcpu, vector, err);
@@ -3732,9 +3769,13 @@ 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)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 47e7427d0395..a770a1c7ddd2 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -230,8 +230,8 @@ struct vcpu_svm {
 	bool nmi_singlestep;
 	u64 nmi_singlestep_guest_rflags;
 
-	unsigned int3_injected;
-	unsigned long int3_rip;
+	unsigned soft_int_injected;
+	unsigned long soft_int_linear_rip;
 
 	/* optional nested SVM features that are enabled for this guest  */
 	bool nrips_enabled                : 1;

base-commit: 26f97f8db06dc08a2b6a48692cdc1d89b288905d
-- 
2.35.1.1094.g7c7d902a7c-goog


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