[PATCH 18/19] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps

From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Li RongQing <lirongqing@baidu.com>
Subject: [PATCH 18/19] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps
Date: Wed, 31 Aug 2022 00:35:05 +0000	[thread overview]
Message-ID: <20220831003506.4117148-19-seanjc@google.com> (raw)
In-Reply-To: <20220831003506.4117148-1-seanjc@google.com>

Drop writes to APIC_RRR, a.k.a. Remote Read Data Register, on AVIC
unaccelerated write traps.  The register is read-only and isn't emulated
by KVM.  Sending the register through kvm_apic_write_nodecode() will
result in screaming when x2APIC is enabled due to the unexpected failure
to retrieve the MSR (KVM expects that only "legal" accesses will trap).

Fixes: 4d1d7942e36a ("KVM: SVM: Introduce logic to (de)activate x2AVIC mode")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/avic.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index dad5affe44c1..b2033a56010c 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -675,6 +675,9 @@ static int avic_unaccel_trap_write(struct kvm_vcpu *vcpu)
 	case APIC_DFR:
 		avic_handle_dfr_update(vcpu);
 		break;
+	case APIC_RRR:
+		/* Ignore writes to Read Remote Data, it's read-only. */
+		return 1;
 	default:
 		break;
 	}
-- 
2.37.2.672.g94769d06f0-goog

