On Fri, Jul 7, 2017 at 1:34 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> On 07/07/2017 10:22, Paolo Bonzini wrote:
>>
>>
>> On 06/07/2017 21:52, Jim Mattson wrote:
>>> Allow VMWRITE in L1 to modify VM-exit information fields and report
>>> this feature in L1's IA32_VMX_MISC MSR.
>>>
>>> Note that this feature is a prerequisite for kvm in L1 to use VMCS
>>> shadowing, once that feature is available.
>>>
>>> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
>>> ---
>>> arch/x86/kvm/vmx.c | 105 ++++++++++++++++++++---------------------------------
>>> 1 file changed, 39 insertions(+), 66 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index b4cfdcfdc1c1..72f295510f76 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -7467,14 +7447,7 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
>>> }
>>> }
>>>
>>> -
>>> field = kvm_register_readl(vcpu, (((vmx_instruction_info) >> 28) & 0xf));
>>> - if (vmcs_field_readonly(field)) {
>>> - nested_vmx_failValid(vcpu,
>>> - VMXERR_VMWRITE_READ_ONLY_VMCS_COMPONENT);
>>> - return kvm_skip_emulated_instruction(vcpu);
>>> - }
>>> -
>>> if (vmcs12_write_any(vcpu, field, field_value) < 0) {
>>> nested_vmx_failValid(vcpu, VMXERR_UNSUPPORTED_VMCS_COMPONENT);
>>> return kvm_skip_emulated_instruction(vcpu);
>>>
>>
>> vmcs_field_readonly is now unused. With that removed,
>>
>> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> Actually, no. The error must be kept if the host has disabled the
> feature with a KVM_SET_MSR ioctl for MSR_IA32_VMX_MISC.
>
Coming back to this patch set...
Is there a good reason to allow userspace to clear
MSR_IA32_VMX_MISC_VMWRITE_SHADOW_RO_FIELDS? It's not yet possible to
migrate a VMX-capable VM (though I think that ability is imminent), so
there are no compatibility issues. Why not just force this on?
