Re: [PATCH] Paging and memory sharing for HVM guests

[Patrick Colp <pjcolp@cs.ubc.ca>]

Konrad Rzeszutek Wilk wrote:
>> A new ioctl seems like the reasonable approach. And as you, say if we're  
>> going to have a new ioctl, then let's do it right. When calling  
>> xc_map_foreign_batch(), is there any requirement that the pfns you pass 
>> in are contiguous (ordering incrementally)? If not, then I think 
>> completely over-writing the MFNs is probably the wrong thing to do, as it 
>> requires callers to keep two copies of the array to find out which pages 
>> didn't map. I would be more in favour of returning a bit vector. As far 
> 
> I would suggest you look in xen_exchange_memory in the linux kernel. One
> of its customers is xen_create_contiguous_region which replaces MFNs
> with ones underneath the 4GB.
> 
> There is a requirement in making the PFNs contigous but that is b/c
> the Xen side loops over it assuming incremental order.

If we know that the PFNs have to be contiguous (and we're happy having this 
be a requirement), then completely overwriting the MFNs is probably easier 
than returning a bit vector (and wouldn't require extra support in libxc).


Patrick