Messages in this thread | | | From | Tejun Heo <> | Subject | [GIT PATCH] x86,percpu: fix pageattr handling with remap allocator | Date | Thu, 14 May 2009 21:49:46 +0900 |
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Hello,
Upon ack, please pull from the following git tree.
git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git x86-percpu-pageattr
This patchset fixes subtile bug in pageattr handling when remap percpu first chunk allocator is in use and implements percpu_alloc kernel parameter so that allocator can be selected from boot prompt.
This problem was spotted by Jan Beulich.
The remap allocator allocates a PMD page per cpu, returns whatever is unnecessary to the page allocator and remaps the PMD page into vmalloc area to construct the first percpu chunk. This is to take advantage of large page mapping. However this creates active aliases for the recycled pages. When some user allocates the recycled pages and tries to change pageattr on it, remapped PMD alias might end up having different attributes with the regular page mapped addresses which can lead to subtle data corruption according to Andi.
Similar problem exists for the high mapped area of x86_64 kernel which is handled by detecting the alias and splitting up the high map PMD and applying the same attributes there. This patch implements the same workaround for remapped first chunk.
Also, it's still unclear whether the remap allocator is worth the trouble. Andi thinks it would be better to simply use 4k mapping on NUMA machines as PMD TLB is much more precious resource than PTE TLB. To ease testing, this patch implements percpu_alloc kernel parameter which allows explicitly selecting which allocator to use.
This patchset contains the following four patches.
0001-x86-prepare-setup_pcpu_remap-for-pageattr-fix.patch 0002-x86-simplify-cpa_process_alias.patch 0003-x86-fix-pageattr-handling-for-remap-percpu-allocato.patch 0004-x86-implement-percpu_alloc-kernel-parameter.patch
0001-0002 preps for pageattr fix. 0003 fixes the pageattr bug. 0004 implements percpu_alloc kernel parameter.
This patchset is on top of the current linux-2.6#master (210af919c949a7d6bd330916ef376cec2907d81e) and contains the following changes.
Documentation/kernel-parameters.txt | 6 + arch/x86/include/asm/percpu.h | 9 + arch/x86/kernel/setup_percpu.c | 186 ++++++++++++++++++++++++++---------- arch/x86/mm/pageattr.c | 59 +++++++---- mm/percpu.c | 13 +- 5 files changed, 197 insertions(+), 76 deletions(-)
Thanks.
-- tejun
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