increase evtchn limits

[Mukesh Rathor <mukesh.rathor@oracle.com>]

Hi,

I'm trying to boot up with lot more than 32 vcpus on this very large box.
I overcame vcpu_info[MAX_VIRT_CPUS] by doing vcpu placement hypercall
in guest, but now running into evt channel limit (lots of devices):

       unsigned long evtchn_pending[sizeof(unsigned long) * 8];

which limits to 512 max for my 64bit dom0. The only recourse seems to 
create a new struct shared_info_v2{}, and re-arrange it a bit with lot 
more event channels. Since, start_info has magic with version info, I 
can just check that in guest and use new shared_info...(doing the design 
on the fly here). I can create a new vcpuop saying the guest is using 
newer version.  Or forget new version of shared_info{}, I can just
put evtchn stuff in my own mfn and tell hypervisor to relocate it,
(just like vcpu_info does) via new VCPUOP_ call.

Keir, what do you think?

thanks,
Mukesh