From 74260714c56de4f967fcb2f17a8656bc574b75be Mon Sep 17 00:00:00 2001
From: Jeremy Fitzhardinge <jeremy@xensource.com>
Date: Tue, 16 Oct 2007 11:51:30 -0700
Subject: xen: lock pte pages while pinning/unpinning

When a pagetable is created, it is made globally visible in the rmap
prio tree before it is pinned via arch_dup_mmap(), and remains in the
rmap tree while it is unpinned with arch_exit_mmap().

This means that other CPUs may race with the pinning/unpinning
process, and see a pte between when it gets marked RO and actually
pinned, causing any pte updates to fail with write-protect faults.

As a result, all pte pages must be properly locked, and only unlocked
once the pinning/unpinning process has finished.

In order to avoid taking spinlocks for the whole pagetable - which may
overflow the PREEMPT_BITS portion of preempt counter - it locks and pins
each pte page individually, and then finally pins the whole pagetable.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickens <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <ak@suse.de>
Cc: Keir Fraser <keir@xensource.com>
Cc: Jan Beulich <jbeulich@novell.com>
---
 mm/Kconfig | 1 -
 1 file changed, 1 deletion(-)

(limited to 'mm')

diff --git a/mm/Kconfig b/mm/Kconfig
index a7609cbcb00d..e24d348083c3 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -137,7 +137,6 @@ config SPLIT_PTLOCK_CPUS
 	int
 	default "4096" if ARM && !CPU_CACHE_VIPT
 	default "4096" if PARISC && !PA20
-	default "4096" if XEN
 	default "4"
 
 #
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