On Thu, Jan 14, 2016 at 11:30:43AM +0300, Pavel Fedin wrote:
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -3359,6 +3359,14 @@ Hyper-V SynIC state change. Notification is used to remap SynIC
> > event/message pages and to enable/disable SynIC messages/events processing
> > in userspace.
> >
> > + /* KVM_EXIT_HYPERV_HCALL */
> > + struct {
> > + __u64 input;
> > + __u64 params[2];
> > + __u64 result;
> > + } hv_hcall;
> > +Indicates that the VCPU exits into userspace to process some guest
> > +Hyper-V hypercalls.
>
> Why introducing this? We already have KVM_EXIT_HYPERCALL, which is exactly the same. AFAIK it's not used at the moment.
> Additionally, in theory we could have hypercalls handled in userspace for something else except HyperV. And not only for x86.
We thought reusing KVM_EXIT_HYPERCALL was a bad idea exactly because of
that. Hypercalls are not universal, the calling and return conventions
are hypervisor-specific. KVM already has to make the decision that the
particular vmexit is a HyperV hypercall; it appears unnatural to then
pass the data on to userspace in a generic structure and have them make
that decision again.
Roman.
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