[PATCH 3.11 103/137] ARM: 8115/1: LPAE: reduce damage caused by idmap to virtual memory layout

From: Luis Henriques
Date: Mon Aug 18 2014 - 05:36:10 EST


3.11.10.15 -stable review patch. If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <k.khlebnikov@xxxxxxxxxxx>

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@xxxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/