xen: mask _PAGE_PCD from ptes
_PAGE_PCD maps a page with caching disabled, which is typically used for mapping harware registers. Xen never allows it to be set on a mapping, and unprivileged guests never need it since they can't see the real underlying hardware. However, some uncached mappings are made early when probing the (non-existent) APIC, and its OK to mask off the PCD flag in these cases. This became necessary because Xen started checking for this bit, rather than silently masking it off. Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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