linux-kernel - [PATCH v2 04/14] KVM: x86: Don't attempt VMWare emulation on #GP with non-zero error code

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Message-Id: <20190827214040.18710-5-sean.j.christopherson@intel.com>
Date:   Tue, 27 Aug 2019 14:40:30 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Liran Alon <liran.alon@...cle.com>
Subject: [PATCH v2 04/14] KVM: x86: Don't attempt VMWare emulation on #GP with non-zero error code

The VMware backdoor hooks #GP faults on IN{S}, OUT{S}, and RDPMC, none
of which generate a non-zero error code for their #GP.  Re-injecting #GP
instead of attempting emulation on a non-zero error code will allow a
future patch to move #GP injection (for emulation failure) into
kvm_emulate_instruction() without having to plumb in the error code.

Reviewed-and-tested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Reviewed-by: Liran Alon <liran.alon@...cle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/svm.c     | 10 +++++++++-
 arch/x86/kvm/vmx/vmx.c | 12 +++++++++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1f220a85514f..7242142573d6 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2772,12 +2772,20 @@ static int gp_interception(struct vcpu_svm *svm)
 
 	WARN_ON_ONCE(!enable_vmware_backdoor);
 
+	/*
+	 * VMware backdoor emulation on #GP interception only handles IN{S},
+	 * OUT{S}, and RDPMC, none of which generate a non-zero error code.
+	 */
+	if (error_code) {
+		kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
+		return 1;
+	}
 	er = kvm_emulate_instruction(vcpu,
 		EMULTYPE_VMWARE | EMULTYPE_NO_UD_ON_FAIL);
 	if (er == EMULATE_USER_EXIT)
 		return 0;
 	else if (er != EMULATE_DONE)
-		kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
+		kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
 	return 1;
 }
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 18286e5b5983..8a65e1122376 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4509,12 +4509,22 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 
 	if (!vmx->rmode.vm86_active && is_gp_fault(intr_info)) {
 		WARN_ON_ONCE(!enable_vmware_backdoor);
+
+		/*
+		 * VMware backdoor emulation on #GP interception only handles
+		 * IN{S}, OUT{S}, and RDPMC, none of which generate a non-zero
+		 * error code on #GP.
+		 */
+		if (error_code) {
+			kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
+			return 1;
+		}
 		er = kvm_emulate_instruction(vcpu,
 			EMULTYPE_VMWARE | EMULTYPE_NO_UD_ON_FAIL);
 		if (er == EMULATE_USER_EXIT)
 			return 0;
 		else if (er != EMULATE_DONE)
-			kvm_queue_exception_e(vcpu, GP_VECTOR, error_code);
+			kvm_queue_exception_e(vcpu, GP_VECTOR, 0);
 		return 1;
 	}
 
-- 
2.22.0