On 04/11/2016 21:34, David Matlack wrote:
> On Mon, Oct 31, 2016 at 6:37 PM, Kyle Huey <m...@kylehuey.com> wrote:
>> + case MSR_PLATFORM_INFO:
>> + /* cpuid faulting is supported */
>> + msr_info->data = PLATINFO_CPUID_FAULT;
>> + break;
>
> This could break save/restore, if for example, a VM is migrated to a
> version of KVM without MSR_PLATFORM_INFO support. I think the way to
> handle this is to make MSR_PLATFORM_INFO writeable (but only from
> userspace) so that hypervisors can defend themselves (by setting this
> MSR to 0).
Right---and with my QEMU hat on, this feature will have to be enabled
manually on the command line because of the way QEMU supports running
with old kernels. :( This however does not impact the KVM patch.
We may decide that, because CPUID faulting doesn't have a CPUID bit and
is relatively a "fringe" feature, we are okay if the kernel enables this
unconditionally and then userspace can arrange to block migration (in
QEMU this would use a subsection). David, Eduardo, opinions?
>
>> + case MSR_MISC_FEATURES_ENABLES:
>> + msr_info->data = 0;
>> + if (vcpu->arch.cpuid_fault)
>> + msr_info->data |= CPUID_FAULT_ENABLE;
>> + break;
>
> MSR_MISC_FEATURES_ENABLES should be added to emulated_msrs[] so that
> the hypervisor will maintain the value of CPUID_FAULT_ENABLE across a
> save/restore.
This is definitely necessary. Thanks David.
Paolo
>> default:
>> if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
>> return kvm_pmu_get_msr(vcpu, msr_info->index,
>> &msr_info->data);
>> if (!ignore_msrs) {
>> vcpu_unimpl(vcpu, "unhandled rdmsr: 0x%x\n",
>> msr_info->index);
>> return 1;
>> } else {
>> vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n",
>> msr_info->index);
>> @@ -7493,16 +7507,18 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool
>> init_event)
>> kvm_update_dr0123(vcpu);
>> vcpu->arch.dr6 = DR6_INIT;
>> kvm_update_dr6(vcpu);
>> vcpu->arch.dr7 = DR7_FIXED_1;
>> kvm_update_dr7(vcpu);
>>
>> vcpu->arch.cr2 = 0;
>>
>> + vcpu->arch.cpuid_fault = false;
>> +
>> kvm_make_request(KVM_REQ_EVENT, vcpu);
>> vcpu->arch.apf.msr_val = 0;
>> vcpu->arch.st.msr_val = 0;
>>
>> kvmclock_reset(vcpu);
>>
>> kvm_clear_async_pf_completion_queue(vcpu);
>> kvm_async_pf_hash_reset(vcpu);
>> --
>> 2.10.2
>>
>> --
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>
