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Merge tag 'x86-splitlock-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

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Pull x86 splitlock updates from Thomas Gleixner:
 "Support for 'split lock' detection:

  Atomic operations (lock prefixed instructions) which span two cache
  lines have to acquire the global bus lock. This is at least 1k cycles
  slower than an atomic operation within a cache line and disrupts
  performance on other cores. Aside of performance disruption this is a
  unpriviledged form of DoS.

  Some newer CPUs have the capability to raise an #AC trap when such an
  operation is attempted. The detection is by default enabled in warning
  mode which will warn once when a user space application is caught. A
  command line option allows to disable the detection or to select fatal
  mode which will terminate offending applications with SIGBUS"

* tag 'x86-splitlock-2020-03-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/split_lock: Avoid runtime reads of the TEST_CTRL MSR
  x86/split_lock: Rework the initialization flow of split lock detection
  x86/split_lock: Enable split lock detection by kernel
This commit is contained in:
Linus Torvalds
2020-03-30 19:35:52 -07:00
parent d5f744f9a2 a6a6074103
commit 2853d5fafb
9 changed files with 258 additions and 3 deletions
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22
Documentation/admin-guide/kernel-parameters.txt
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@@ -4711,6 +4711,28 @@
spia_pedr=
spia_peddr=
split_lock_detect=
[X86] Enable split lock detection
When enabled (and if hardware support is present), atomic
instructions that access data across cache line
boundaries will result in an alignment check exception.
off - not enabled
warn - the kernel will emit rate limited warnings
about applications triggering the #AC
exception. This mode is the default on CPUs
that supports split lock detection.
fatal - the kernel will send SIGBUS to applications
that trigger the #AC exception.
If an #AC exception is hit in the kernel or in
firmware (i.e. not while executing in user mode)
the kernel will oops in either "warn" or "fatal"
mode.
srcutree.counter_wrap_check [KNL]
Specifies how frequently to check for
grace-period sequence counter wrap for the