From e3a1f6cac1fe20e7ac01d96c914c25726723a64e Mon Sep 17 00:00:00 2001
From: David Vrabel <david.vrabel@citrix.com>
Date: Thu, 19 Feb 2015 13:06:53 +0000
Subject: [PATCH] x86: pte_protnone() and pmd_protnone() must check entry is
 not present

Since _PAGE_PROTNONE aliases _PAGE_GLOBAL it is only valid if
_PAGE_PRESENT is clear.  Make pte_protnone() and pmd_protnone() check
for this.

This fixes a 64-bit Xen PV guest regression introduced by 8a0516ed8b90
("mm: convert p[te|md]_numa users to p[te|md]_protnone_numa").  Any
userspace process would endlessly fault.

In a 64-bit PV guest, userspace page table entries have _PAGE_GLOBAL set
by the hypervisor.  This meant that any fault on a present userspace
entry (e.g., a write to a read-only mapping) would be misinterpreted as
a NUMA hinting fault and the fault would not be correctly handled,
resulting in the access endlessly faulting.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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