Re: [PATCH v2] xen/balloon: Fix mapping PG_offline pages to user space

From: Juergen Gross
Date: Thu Mar 14 2019 - 12:05:40 EST

On 14/03/2019 17:02, David Hildenbrand wrote:
> The XEN balloon driver - in contrast to other balloon drivers - allows
> to map some inflated pages to user space. Such pages are allocated via
> alloc_xenballooned_pages() and freed via free_xenballooned_pages().
> The pfn space of these allocated pages is used to map other things
> by the hypervisor using hypercalls.
> Pages marked with PG_offline must never be mapped to user space (as
> this page type uses the mapcount field of struct pages).
> So what we can do is, clear/set PG_offline when allocating/freeing an
> inflated pages. This way, most inflated pages can be excluded by
> dumping tools and the "reused for other purpose" balloon pages are
> correctly not marked as PG_offline.
> Fixes: 77c4adf6a6df (xen/balloon: mark inflated pages PG_offline)
> Reported-by: Julien Grall <julien.grall@xxxxxxx>
> Tested-by: Julien Grall <julien.grall@xxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>

Reviewed-by: Juergen Gross <jgross@xxxxxxxx>