x86: don't allow page table updates on non-PV page tables in do_mmu_update()

x86: don't allow page table updates on non-PV page tables in do_mmu_update()

paging_write_guest_entry() and paging_cmpxchg_guest_entry() aren't
consistently supported for non-PV guests (they'd deref NULL for PVH or
non-HAP HVM ones). Don't allow respective MMU_* operations on the
page tables of such domains.

This is CVE-2014-8594 / XSA-109.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>
master commit: e4292c5aac41b80f33d4877104348d5ee7c95aa4
master date: 2014-11-18 14:15:21 +0100