linux-kernel - [PATCH] do not try to sync identity map for non-mapped pages

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Message-Id: <20130306231009.D782087E@kernel.stglabs.ibm.com>
Date:	Wed, 06 Mar 2013 15:10:09 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	bp@...en8.de, hpa@...ux.intel.com,
	penguin-kernel@...ove.sakura.ne.jp,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: [PATCH] do not try to sync identity map for non-mapped pages

kernel_map_sync_memtype() is called from a variety of contexts.  The
pat.c code that calls it seems to ensure that it is not called for
non-ram areas by checking via pat_pagerange_is_ram().  It is important
that it only be called on the actual identity map because there *IS*
no map to sync for highmem pages, or for memory holes.

The ioremap.c uses are not as careful as those from pat.c, and call
kernel_map_sync_memtype() on PCI space which is in the middle of the
kernel identity map _range_, but is not actually mapped.

This patch adds a check to kernel_map_sync_memtype() which probably
duplicates some of the checks already in pat.c.  But, it is necessary
for the ioremap.c uses and shouldn't hurt other callers.

I have reproduced this bug and this patch fixes it for me

	https://lkml.org/lkml/2013/2/5/396

Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>
---

 linux-2.6.git-dave/arch/x86/mm/pat.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff -puN arch/x86/mm/pat.c~dont-flush-map-for-non-ram-pages arch/x86/mm/pat.c
--- linux-2.6.git/arch/x86/mm/pat.c~dont-flush-map-for-non-ram-pages	2013-03-06 15:03:56.403628100 -0800
+++ linux-2.6.git-dave/arch/x86/mm/pat.c	2013-03-06 15:03:56.419628258 -0800
@@ -563,6 +563,13 @@ int kernel_map_sync_memtype(u64 base, un
 	if (base > __pa(high_memory-1))
 		return 0;

+	/*
+	 * some areas in the middle of the kernel identity range
+	 * are not mapped, like the PCI space.
+	 */
+	if (!page_is_ram(base >> PAGE_SHIFT))
+		return 0;
+
 	id_sz = (__pa(high_memory-1) <= base + size) ?
 				__pa(high_memory) - base :
 				size;
diff -puN arch/x86/mm/ioremap.c~dont-flush-map-for-non-ram-pages arch/x86/mm/ioremap.c
_

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