linux-kernel - [PATCH] KVM: SVM: Remove bogus WARN and emulation if guest #GPs with EFER.SVME=1

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Message-Id: <20210204023536.3397005-1-seanjc@google.com>
Date:   Wed,  3 Feb 2021 18:35:36 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.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, Bandan Das <bsd@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH] KVM: SVM: Remove bogus WARN and emulation if guest #GPs with EFER.SVME=1

Immediately reinject #GP (if intercepted) if the VMware backdoor is
disabled and the instruction is not affected by the erratum that causes
bogus #GPs on SVM instructions.  It is completely reasonable for the
guest to take a #GP(0) with EFER.SVME=1, e.g. when probing an MSR, and
attempting emulation on an unknown instruction is obviously not good.

Fixes: b3f4e11adc7d ("KVM: SVM: Add emulation support for #GP triggered by SVM instructions")
Cc: Bandan Das <bsd@...hat.com>
Cc: Maxim Levitsky <mlevitsk@...hat.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f53e6377a933..707a2f85bcc6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2263,7 +2263,8 @@ static int gp_interception(struct vcpu_svm *svm)
 	opcode = svm_instr_opcode(vcpu);
 
 	if (opcode == NONE_SVM_INSTR) {
-		WARN_ON_ONCE(!enable_vmware_backdoor);
+		if (!enable_vmware_backdoor)
+			goto reinject;
 
 		/*
 		 * VMware backdoor emulation on #GP interception only handles
-- 
2.30.0.365.g02bc693789-goog