]> git.karo-electronics.de Git - karo-tx-linux.git/commit
ARM: 5691/1: fix cache aliasing issues between kmap() and kmap_atomic() with highmem
authorNicolas Pitre <nico@cam.org>
Thu, 3 Sep 2009 20:45:59 +0000 (21:45 +0100)
committerRussell King <rmk+kernel@arm.linux.org.uk>
Fri, 4 Sep 2009 18:20:07 +0000 (19:20 +0100)
commit7929eb9cf643ae416e5081b2a6fa558d37b9854c
treec4cbaa5ccdd1c929eba802374d80191b6f90e16c
parentc47a830c08a26a7c210ae16a0ffe3f56ba86ea69
ARM: 5691/1: fix cache aliasing issues between kmap() and kmap_atomic() with highmem

Let's suppose a highmem page is kmap'd with kmap().  A pkmap entry is
used, the page mapped to it, and the virtual cache is dirtied.  Then
kunmap() is used which does virtually nothing except for decrementing a
usage count.

Then, let's suppose the _same_ page gets mapped using kmap_atomic().
It is therefore mapped onto a fixmap entry instead, which has a
different virtual address unaware of the dirty cache data for that page
sitting in the pkmap mapping.

Fortunately it is easy to know if a pkmap mapping still exists for that
page and use it directly with kmap_atomic(), thanks to kmap_high_get().

And actual testing with a printk in the added code path shows that this
condition is actually met *extremely* frequently.  Seems that we've been
quite lucky that things have worked so well with highmem so far.

Cc: stable@kernel.org
Signed-off-by: Nicolas Pitre <nico@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
arch/arm/mm/highmem.c