linux-kernel - [RFC Part2 PATCH v3 25/26] KVM: SVM: Do not install #UD intercept when SEV is enabled

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Date:   Mon, 24 Jul 2017 15:03:02 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        \"Radim Krčmář\" 
        <rkrcmar@...hat.com>, Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [RFC Part2 PATCH v3 25/26] KVM: SVM: Do not install #UD intercept when SEV is enabled

On #UD, x86_emulate_instruction() fetches the data from guest memory and
decodes the instruction bytes to assist further. When SEV is enabled, the
instruction bytes will be encrypted using the guest-specific key, hypervisor
will no longer able to fetch the instruction bytes to assist UD handling.
By not installing intercept we let the guest receive and handle #UD.

Signed-off-by: Brijesh Singh <brijesh.singh@....com>
---
 arch/x86/kvm/svm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 64b9f60..4581d03 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1432,8 +1432,10 @@ static void init_vmcb(struct vcpu_svm *svm)
 		svm->vmcb->control.virt_ext |= VIRTUAL_VMLOAD_VMSAVE_ENABLE_MASK;
 	}
 
-	if (sev_guest(svm->vcpu.kvm))
+	if (sev_guest(svm->vcpu.kvm)) {
 		svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ENABLE;
+		clr_exception_intercept(svm, UD_VECTOR);
+	}
 
 	mark_all_dirty(svm->vmcb);
 
-- 
2.9.4