kernel-packages team mailing list archive

[Feng Kan <fkan@xxxxxxx>]

The crash is due to the incorrect implementation of the copy_to_user
potion's abort handler zeroing out destination buffers. The code has
been corrected by forking different handlers for copy_from and copy_to
user source files. We have a test that runs specweb, iperf and fio that
reproduce the crash immediately. The new patch attached has ran the same
test for over 50 hours without issues. I have also attached both the
crash log and the non crashing log as well.

** Patch added: "New copy to/from optimization"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1400349/+attachment/4276593/+files/0001-arm64-optimized-copy_to_user-and-copy_from_user-asse.patch

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https://bugs.launchpad.net/bugs/1400349

Title:
  [SRU] new arm64 optimized copy_to_user and copy_from_user assembly
  code

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  [Impact]
  The copy_{to,from}_user implementations in the Ubuntu kernel are suboptimal. Optimized implementations have been submitted upstream and have shown a significant improvement in network performance.

  [Test Case]
  Generate traffic from one node to another using iperf.

  [Regression Risk]
  These functions are obviously used heavily throughout the kernel, so a defect here could have significant impact. This risk is mitigated by using an implementation heavily based on the linaro string libraries (which are used in other places already, e.g. glibc), and through active testing of this patch on real hardware using a trusty-kernel base. The new patch will also undergo regression testing to ensure the memory corruption issue of the previous patch does not exist.

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