Re: [Qemu-devel] [PATCH v1 4/5] kvm/x86: Hyper-V VMBus hypercall userspace exit

[Paolo Bonzini]

On 20/01/2016 18:31, 'Roman Kagan' wrote:
> On Wed, Jan 20, 2016 at 06:02:25PM +0100, Paolo Bonzini wrote:
>>
>>
>> On 20/01/2016 16:20, 'Roman Kagan' wrote:
>>>>> So we should not add a new exit
>>> Why?  VCPU exit codes are not a scarse resource.
>>
>> Indeed, but grouping makes things easier to understand.
>>
>>> So far we've envisaged two reasons for VCPU exit related to hyper-v: one
>>> for hyper-v MSRs and the other for hypercalls.  Since there was a
>>> discussion on implementing generic MSR access by Peter we thought it
>>> wiser to introduce a new VCPU exit for hyper-v hypercalls to avoid
>>> interfering with the MSR implementation.
>>
>> That's a good idea.  However, I think I'm not going to accept the MSR
>> exit feature, and then the current Hyper-V exit API makes some sense
>> indeed (it's just 3 values, transferring them all at once is not
>> expensive at all).
> 
> OK can we please sum up (as I'm now a bit confused) what we do now:
> 
> 1) use a single vcpu exit for both Hyper-V cases (which implies we need
>    to fix this patchset to add the subcode for hypercalls)

This.

Paolo

>  or
> 
> 2) use individual vcpu exits for Hyper-V MSRs and for Hyper-V hypercalls
>    (which implies we need to submit an incremental patch dropping the
>    subcode from Hyper-V MSR exit and renaming it to better describe the
>    reality)?
> 
> Thanks,
> Roman.
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