[PATCH v3 27/28] KVM: SVM: Ignore writes to Remote Read Data on AVIC write traps

Sean Christopherson
2022-09-20T23:35:09Z

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>
---
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 17e64b056e4e..953b1fd14b6d 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -631,6 +631,9 @@ 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;
}
--
2.37.3.968.ga6b4b080e4-goog