Hi Sean,
> @@ -4265,6 +4265,16 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu,
> clgi();
> kvm_load_guest_xsave_state(vcpu);
>
> + /*
> + * Hardware only context switches DEBUGCTL if LBR virtualization is
> + * enabled. Manually load DEBUGCTL if necessary (and restore it after
> + * VM-Exit), as running with the host's DEBUGCTL can negatively affect
> + * guest state and can even be fatal, e.g. due to Bus Lock Detect.
> + */
> + if (!(svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK) &&
> + vcpu->arch.host_debugctl != svm->vmcb->save.dbgctl)
> + update_debugctlmsr(0);
^^^^^^^^^^^^^^^^^^^^^
You mean:
update_debugctlmsr(svm->vmcb->save.dbgctl);
?
Somewhat related but independent: CPU automatically clears DEBUGCTL[BTF]
on #DB exception. So, when DEBUGCTL is save/restored by KVM (i.e. when
LBR virtualization is disabled), it's KVM's responsibility to clear
DEBUGCTL[BTF].
---
@@ -2090,6 +2090,14 @@ static int db_interception(struct kvm_vcpu *vcpu)
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) &&
!svm->nmi_singlestep) {
u32 payload = svm->vmcb->save.dr6 ^ DR6_ACTIVE_LOW;
+
+ /*
+ * CPU automatically clears DEBUGCTL[BTF] on #DB exception.
+ * Simulate it when DEBUGCTL isn't auto save/restored.
+ */
+ if (!(svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK))
+ svm->vmcb->save.dbgctl &= ~0x2;
+
kvm_queue_exception_p(vcpu, DB_VECTOR, payload);
return 1;
}
---
Thanks,
Ravi
