[PATCH v4 4/4] Documentation/admin-guide: Change doc for split_lock_detect parameter

[Fenghua Yu <fenghua.yu@intel.com>]

Since #DB for bus lock detect changes the split_lock_detect parameter,
update the documentation for the changes.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
---
Change Log:
v4:
- Fix a ratelimit wording issue in the doc (Randy).
- Patch 4 is acked by Randy (Randy).

v3:
- Enable Bus Lock Detection when fatal to handle bus lock from non-WB
  (PeterZ).

v1:
- Fix a few wording issues (Randy).

RFC v2:
- Simplify the documentation (Randy).

 .../admin-guide/kernel-parameters.txt         | 30 +++++++++++++++----
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 44fde25bb221..28228539b02a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5051,27 +5051,45 @@
 	spia_peddr=
 
 	split_lock_detect=
-			[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 #DB 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. If both features are enabled in
+				  hardware, split lock triggers #AC and bus
+				  lock from non-WB triggers #DB.
+
+			ratelimit:N -
+				  Set rate limit to N bus locks per second
+				  for bus lock detection. 0 < N <= HZ/2.
+				  Only applied to non-root users.
+
+				  N/A for split lock detection.
 
 			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.
 
+			#DB exception for bus lock is triggered only when
+			CPL > 0.
+
 	srbds=		[X86,INTEL]
 			Control the Special Register Buffer Data Sampling
 			(SRBDS) mitigation.
-- 
2.29.2