change_page_attr on x86-64 only flushed the TLB for pages that got
reverted. That's not correct: it has to be flushed in all cases.

This bug was added in some earlier changes.

Just flush all pages for now.

This could be done more efficiently, but for this late in the release
this seem to be the best fix.

Pointed out by Jan Beulich
Signed-off-by: NAndi Kleen <ak@suse.de>