Re: [PATCHv1] xen/balloon: disable memory hotplug in PV guests

[David Vrabel <david.vrabel@citrix.com>]

On 09/03/15 14:10, David Vrabel wrote:
> Memory hotplug doesn't work with PV guests because:
> 
>   a) The p2m cannot be expanded to cover the new sections.

Broken by 054954eb051f35e74b75a566a96fe756015352c8 (xen: switch to
linear virtual mapped sparse p2m list).

This one would be non-trivial to fix.  We'd need a sparse set of
vm_area's for the p2m or similar.

>   b) add_memory() builds page tables for the new sections which means
>      the new pages must have valid p2m entries (or a BUG occurs).

After some more testing this appears to be broken by:

25b884a83d487fd62c3de7ac1ab5549979188482 (x86/xen: set regions above the
end of RAM as 1:1) included 3.16.

This one can be trivially fixed by setting the new sections in the p2m
to INVALID_P2M_ENTRY before calling add_memory().

David