[PATCH v2 08/14] KVM: x86: Exit to userspace on emulation skip failure

[Sean Christopherson <sean.j.christopherson@intel.com>]

Kill a few birds with one stone by forcing an exit to userspace on skip
emulation failure.  This removes a reference to EMULATE_FAIL, fixes a
bug in handle_ept_misconfig() where it would exit to userspace without
setting run->exit_reason, and fixes a theoretical bug in SVM's
task_switch_interception() where it would overwrite run->exit_reason on
a return of EMULATE_USER_EXIT.

Note, this technically doesn't fully fix task_switch_interception()
as it now incorrectly handles EMULATE_FAIL, but in practice there is no
bug as EMULATE_FAIL will never be returned for EMULTYPE_SKIP.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/svm.c | 4 ++--
 arch/x86/kvm/x86.c | 9 +++++++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c4b72db48bc5..9c46031e96cc 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3885,8 +3885,8 @@ static int task_switch_interception(struct vcpu_svm *svm)
 	    int_type == SVM_EXITINTINFO_TYPE_SOFT ||
 	    (int_type == SVM_EXITINTINFO_TYPE_EXEPT &&
 	     (int_vec == OF_VECTOR || int_vec == BP_VECTOR))) {
-		if (skip_emulated_instruction(&svm->vcpu) != EMULATE_DONE)
-			goto fail;
+		if (skip_emulated_instruction(&svm->vcpu) == EMULATE_USER_EXIT)
+			return 0;
 	}
 
 	if (int_type != SVM_EXITINTINFO_TYPE_SOFT)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bff3320aa78e..1a886ec6957d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6209,6 +6209,13 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu, int emulation_type)
 		return EMULATE_DONE;
 	}
 
+	if (emulation_type & EMULTYPE_SKIP) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		return EMULATE_USER_EXIT;
+	}
+
 	kvm_queue_exception(vcpu, UD_VECTOR);
 
 	if (!is_guest_mode(vcpu) && kvm_x86_ops->get_cpl(vcpu) == 0) {
@@ -6536,8 +6543,6 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 				return EMULATE_DONE;
 			if (ctxt->have_exception && inject_emulated_exception(vcpu))
 				return EMULATE_DONE;
-			if (emulation_type & EMULTYPE_SKIP)
-				return EMULATE_FAIL;
 			return handle_emulation_failure(vcpu, emulation_type);
 		}
 	}
-- 
2.22.0