Re: Scalable Event Channel ABI design (draft A)

[Keir Fraser <keir@xen.org>]

On 06/02/2013 09:38, "Ian Campbell" <Ian.Campbell@citrix.com> wrote:

>>> VCPUOP_register_vcpu_info doesn't require each vcpu_info to be on a page
>>> by itself, even if that happens to be the Linux implementation today (I
>>> haven't checked that).
>> 
>> Having guest agree that vcpu_info grows by size of the per-vcpu control
>> block, if using this new event-channel interface, is reasonable though.
> 
> Can only use this trick once though, so it might be blocking ourselves
> into a future ABI corner.
> 
> Is there a downside to registering the control block separately? The
> guest can always arrange for them to be contiguous if it wants, or if we
> are worried about the number of global mappings then the hypervisor
> could require it shares a page with the vcpu_info but allow the offset
> to be specified separately.

I would say we consider vcpu_info to be versioned, and that using the new
event-channel interface requires use of at least v2 of the vcpu_info
structure. There is a rsvd field in register_vcpu_info hypercall that could
be used for specifying such a thing, although sadly it is not currently
checked to be zero, so we may not actually be able to make use of those
bits.

 -- Keir