[patch 09/57] x86: fix /dev/mem mmap breakage when PAT is disabled

[Greg KH <gregkh@suse.de>]

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2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Ravikiran G Thirumalai <kiran@scalex86.org>

commit 9e41bff2708e420e61e6b89a54c15232857069b1 upstream

Impact: allow /dev/mem mmaps on non-PAT CPUs/platforms

Fix mmap to /dev/mem when CONFIG_X86_PAT is off and CONFIG_STRICT_DEVMEM is
off

mmap to /dev/mem on kernel memory has been failing since the
introduction of PAT (CONFIG_STRICT_DEVMEM=n case).   Seems like
the check to avoid cache aliasing with PAT is kicking in even
when PAT is disabled. The bug seems to have crept in 2.6.26.

This patch makes sure that the mmap to regular
kernel memory succeeds if CONFIG_STRICT_DEVMEM=n and
PAT is disabled, and the checks to avoid cache aliasing
still happens if PAT is enabled.

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Tested-by: Tim Sirianni <tim@scalemp.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 arch/x86/mm/pat.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -403,12 +403,16 @@ static inline int range_is_allowed(unsig
 	return 1;
 }
 #else
+/* This check is needed to avoid cache aliasing when PAT is enabled */
 static inline int range_is_allowed(unsigned long pfn, unsigned long size)
 {
 	u64 from = ((u64)pfn) << PAGE_SHIFT;
 	u64 to = from + size;
 	u64 cursor = from;
 
+	if (!pat_enabled)
+		return 1;
+
 	while (cursor < to) {
 		if (!devmem_is_allowed(pfn)) {
 			printk(KERN_INFO

--