Re: [PATCH] KVM: x86: no need to check CPL for XSETBV on VMX

[Yang Zhang <yang.zhang.wz@gmail.com>]

On 2016/4/15 19:03, Paolo Bonzini wrote:
>
>
> On 15/04/2016 12:55, Yang Zhang wrote:
>>>
>>>>> I don't think this is performance-sensitive, hence it's simpler to keep
>>>>> the code as simple as possible.  For example, if one added XSETBV
>>>>> support to the emulator, your patch would introduce a bug.
>>>>
>>>> In what case we need to decode XSETBV?
>>>
>>> The emulator can be a way to unify code between vmx and svm.  It is an
>>> alternative to writing small wrapper functions such as kvm_set_xcr.
>>
>> I still think the correctness is important.
>
> What correctness?  You said "the CPL check is done by hardware on VMX".
>   Doing the check twice is not incorrect.

Yes, you are right. It cannot be considered as correctness issue.

>
> Unifying code between VMX and SVM is exactly useful because it makes it
> easier to have correct code.
>
> Paolo
>


-- 
best regards
yang