[3.11.y.z extended stable] Patch "ARM: 8115/1: LPAE: reduce damage caused by idmap to virtual memory layout" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    ARM: 8115/1: LPAE: reduce damage caused by idmap to virtual memory layout

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2050bb25ababc5223ef1c2f2f412bb4f001a1574 Mon Sep 17 00:00:00 2001
From: Konstantin Khlebnikov <k.khlebnikov at samsung.com>
Date: Fri, 25 Jul 2014 09:17:12 +0100
Subject: ARM: 8115/1: LPAE: reduce damage caused by idmap to virtual memory
 layout

commit 811a2407a3cf7bbd027fbe92d73416f17485a3d8 upstream.

On LPAE, each level 1 (pgd) page table entry maps 1GiB, and the level 2
(pmd) entries map 2MiB.

When the identity mapping is created on LPAE, the pgd pointers are copied
from the swapper_pg_dir.  If we find that we need to modify the contents
of a pmd, we allocate a new empty pmd table and insert it into the
appropriate 1GB slot, before then filling it with the identity mapping.

However, if the 1GB slot covers the kernel lowmem mappings, we obliterate
those mappings.

When replacing a PMD, first copy the old PMD contents to the new PMD, so
that we preserve the existing mappings, particularly the mappings of the
kernel itself.

[rewrote commit message and added code comment -- rmk]

Fixes: ae2de101739c ("ARM: LPAE: Add identity mapping support for the 3-level page table format")
Signed-off-by: Konstantin Khlebnikov <k.khlebnikov at samsung.com>
Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm/mm/idmap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm/mm/idmap.c b/arch/arm/mm/idmap.c
index 83cb3ac27095..c61d2373408c 100644
--- a/arch/arm/mm/idmap.c
+++ b/arch/arm/mm/idmap.c
@@ -24,6 +24,13 @@ static void idmap_add_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 			pr_warning("Failed to allocate identity pmd.\n");
 			return;
 		}
+		/*
+		 * Copy the original PMD to ensure that the PMD entries for
+		 * the kernel image are preserved.
+		 */
+		if (!pud_none(*pud))
+			memcpy(pmd, pmd_offset(pud, 0),
+			       PTRS_PER_PMD * sizeof(pmd_t));
 		pud_populate(&init_mm, pud, pmd);
 		pmd += pmd_index(addr);
 	} else
--
1.9.1