linux-kernel - [PATCH 5.16 050/200] KVM: SVM: Dont intercept #GP for SEV guests

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Date:   Mon, 31 Jan 2022 11:55:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.16 050/200] KVM: SVM: Dont intercept #GP for SEV guests

From: Sean Christopherson <seanjc@...gle.com>

commit 0b0be065b7563ac708aaa9f69dd4941c80b3446d upstream.

Never intercept #GP for SEV guests as reading SEV guest private memory
will return cyphertext, i.e. emulating on #GP can't work as intended.

Cc: stable@...r.kernel.org
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Liam Merwick <liam.merwick@...cle.com>
Message-Id: <20220120010719.711476-4-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/svm/svm.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -312,7 +312,11 @@ int svm_set_efer(struct kvm_vcpu *vcpu,
 				return ret;
 			}
 
-			if (svm_gp_erratum_intercept)
+			/*
+			 * Never intercept #GP for SEV guests, KVM can't
+			 * decrypt guest memory to workaround the erratum.
+			 */
+			if (svm_gp_erratum_intercept && !sev_guest(vcpu->kvm))
 				set_exception_intercept(svm, GP_VECTOR);
 		}
 	}
@@ -1238,9 +1242,10 @@ static void init_vmcb(struct kvm_vcpu *v
 	 * Guest access to VMware backdoor ports could legitimately
 	 * trigger #GP because of TSS I/O permission bitmap.
 	 * We intercept those #GP and allow access to them anyway
-	 * as VMware does.
+	 * as VMware does.  Don't intercept #GP for SEV guests as KVM can't
+	 * decrypt guest memory to decode the faulting instruction.
 	 */
-	if (enable_vmware_backdoor)
+	if (enable_vmware_backdoor && !sev_guest(vcpu->kvm))
 		set_exception_intercept(svm, GP_VECTOR);
 
 	svm_set_intercept(svm, INTERCEPT_INTR);