KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps

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>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20230106011306.85230-30-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 2c6737f72bd4366b64f4031c9fd9b98068c86d43..ff08732469cbc14626d7567dfc5c31843b551a49 100644 (file)
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -628,6 +628,9 @@ 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;
        }