path: root/Documentation/admin-guide
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authorLinus Torvalds <>2021-04-26 10:09:38 -0700
committerLinus Torvalds <>2021-04-26 10:09:38 -0700
commit64f8e73de08d11cbe01347340db95b4011872ec5 (patch)
treef1a3574482457a91d4eea2af9bc3aeb7b8c26bae /Documentation/admin-guide
parenteea2647e74cd7bd5d04861ce55fa502de165de14 (diff)
parentebca17707e38f2050b188d837bd4646b29a1b0c2 (diff)
Merge tag 'x86-splitlock-2021-04-26' of git://
Pull x86 bus lock detection updates from Thomas Gleixner: "Support for enhanced split lock detection: Newer CPUs provide a second mechanism to detect operations with lock prefix which go accross a cache line boundary. Such operations have to take bus lock which causes a system wide performance degradation when these operations happen frequently. The new mechanism is not using the #AC exception. It triggers #DB and is restricted to operations in user space. Kernel side split lock access can only be detected by the #AC based variant. Contrary to the #AC based mechanism the #DB based variant triggers _after_ the instruction was executed. The mechanism is CPUID enumerated and contrary to the #AC version which is based on the magic TEST_CTRL_MSR and model/family based enumeration on the way to become architectural" * tag 'x86-splitlock-2021-04-26' of git:// Documentation/admin-guide: Change doc for split_lock_detect parameter x86/traps: Handle #DB for bus lock x86/cpufeatures: Enumerate #DB for bus lock detection
Diffstat (limited to 'Documentation/admin-guide')
1 files changed, 16 insertions, 6 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index dd5947a96714..0136cdf7e55d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5111,27 +5111,37 @@
- [X86] Enable split lock detection
+ [X86] Enable split lock detection or bus 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.
+ boundaries will result in an alignment check exception
+ for split lock detection or a debug exception for
+ bus lock detection.
off - not enabled
- warn - the kernel will emit rate limited warnings
+ 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.
+ exception or the #DB exception. This mode is
+ the default on CPUs that support split lock
+ detection or bus lock detection. Default
+ behavior is by #AC if both features are
+ enabled in hardware.
fatal - the kernel will send SIGBUS to applications
- that trigger the #AC exception.
+ that trigger the #AC exception or the #DB
+ exception. Default behavior is by #AC if
+ both features are enabled in hardware.
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"
+ #DB exception for bus lock is triggered only when
+ CPL > 0.
srbds= [X86,INTEL]
Control the Special Register Buffer Data Sampling
(SRBDS) mitigation.