xen/arm: mm: Protect Xen page-table update with a spinlock

xen/arm: mm: Protect Xen page-table update with a spinlock

The function create_xen_entries() may be called concurrently. For
instance, while the vmap allocation is protected by a spinlock, the
mapping is not.

The implementation create_xen_entries() contains quite a few TOCTOU
races such as when allocating the 3rd-level page-tables.

Thankfully, they are pretty hard to reach as page-tables are allocated
once and never released. Yet it is possible, so we need to protect with
a spinlock to avoid corrupting the page-tables.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii.anisov@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>