linux-kernel - [PATCH] x86: ioremap ram check fix

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Date:	Wed, 30 Apr 2008 11:30:24 -0400
From:	Andres Salomon <dilinger@...ued.net>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86: ioremap ram check fix

Hi Ingo,

bdd3cee2e4b7279457139058615ced6c2b41e7de (x86: ioremap(), extend check
to all RAM pages) breaks OLPC's ioremap call.  The ioremap that OLPC uses is:

        romsig = ioremap(0xffffffc0, 16);

The commit that breaks it is basically:

-       for (pfn = phys_addr >> PAGE_SHIFT; pfn < max_pfn_mapped &&
-            (pfn << PAGE_SHIFT) < last_addr; pfn++) {
+       for (pfn = phys_addr >> PAGE_SHIFT;
+                               (pfn << PAGE_SHIFT) < last_addr; pfn++) {
+

Previously, the 'pfn < max_pfn_mapped' check would've caused us to not
enter the loop.  Removing that check means we loop infinitely.  The
reason for that is because pfn is 0xfffff, and last_addr is 0xffffffcf.
The remaining check that is used to exit the loop is not sufficient;
when pfn<<PAGE_SHIFT is 0xfffff000, that is less than 0xffffffcf; when
we increment pfn and it overflows (pfn == 0x100000), pfn<<PAGE_SHIFT
ends up being 0.  That, of course, is less than last_addr.  In effect,
pfn<<PAGE_SHIFT is never lower than last_addr.

The simple fix for this is to limit the last_addr check to the PAGE_MASK;
a patch is below.

Signed-off-by: Andres Salomon <dilinger@...ian.org>
---
 arch/x86/mm/ioremap.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 804de18..fb960f5 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -149,7 +149,8 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
 	 * Don't allow anybody to remap normal RAM that we're using..
 	 */
 	for (pfn = phys_addr >> PAGE_SHIFT;
-				(pfn << PAGE_SHIFT) < last_addr; pfn++) {
+				(pfn << PAGE_SHIFT) < (last_addr & PAGE_MASK);
+				pfn++) {

 		int is_ram = page_is_ram(pfn);

-- 
1.5.5

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