On Mon, Sep 23, 2013 at 02:19:24PM +0100, Steve Capper wrote:
On Tue, Sep 17, 2013 at 10:33:49AM +0100, Steve Capper wrote:
The memory pinning code in uaccess_with_memcpy.c does not check for HugeTLB or THP pmds, and will enter an infinite loop should a __copy_to_user or __clear_user occur against a huge page.
This patch adds detection code for huge pages to pin_page_for_write. As this code can be executed in a fast path it refers to the actual pmds rather than the vma. If a HugeTLB or THP is found (they have the same pmd representation on ARM), the page table spinlock is taken to prevent modification whilst the page is pinned.
On ARM, huge pages are only represented as pmds, thus no huge pud checks are performed. (For huge puds one would lock the page table in a similar manner as in the pmd case).
Two helper functions are introduced; pmd_thp_or_huge will check whether or not a page is huge or transparent huge (which have the same pmd layout on ARM), and pmd_hugewillfault will detect whether or not a page fault will occur on write to the page.
Changes since first RFC:
- The page mask is widened for hugepages to reduce the number of potential locks/unlocks. (A knobbled /dev/zero with its latency reduction chunks removed shows a 2x data rate boost with hugepages backing: dd if=/dev/zero of=/dev/null bs=10M count=1024 )
Signed-off-by: Steve Capper steve.capper@linaro.org
A ping to see if anyone had any questions/comments/flames :-)?
Should it go into the patch system?
IIRC Nicolas wrote the original support, so he should probably be Cc'd with this patch.