Jan Kiszka <jan.kiszka@xxxxxxxxxxx> wrote: > Am 2015-04-28 um 13:43 schrieb Paolo Bonzini: >> On 28/04/2015 13:42, Nadav Amit wrote: >>> It seems strange that the guest is allowed to set IA32_DEBUGCTL MSR for the >>> nested VM and get this value to the physical IA32_DEBUGCTL (see >>> prepare_vmcs02), while it cannot set IA32_DEBUGCTL for itself (see >>> kvm_set_msr_common). >>> >>> Am I missing something? >> >> No, it makes no sense. > > Are you sure that vmx is not allowing direct access to that MSR while in > guest mode? We do save/restore it on all Intel CPUs, see > setup_vmcs_config. Not sure about the AMD situation, though. Unless you explicitly disable the interception of the MSR in the bitmap, you trap WRMSR to this MSR. I guess the original intention of saving/restoring it was to address situations in which the CPU itself implicitly changes it (e.g., clearing LBR when “freezing LBR on PMI” is set). I think that these situations do not apply when the MSR is zeroed, as it happens to be in KVM. Nadav-- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
