xenpaging: Fix c/s 23507:0a29c8c3ddf7 ("update machine_to_phys_mapping[] during page...

xenpaging: Fix c/s 23507:0a29c8c3ddf7 ("update machine_to_phys_mapping[] during page deallocation")

This patch clobbers page owner in free_heap_pages() before we are
finished using it. This means that a subsequent test to determine
whether it is safe to avoid safety TLB flushes incorrectly always
determines that it is safe to do so.

The fix is simple: we can defer the original patch's work until after
we are done with the page-owner field.

Thanks to Christian Limpach for spotting this one.

Signed-off-by: Keir Fraser <keir@xen.org>