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

['Roman Kagan' <rkagan@virtuozzo.com>]

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)

 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.