Documentation/admin-guide: Change doc for split_lock_detect parameter

mainline inclusion
from mainline-v5.12-rc4
commit ebca1770
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I5G10C
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
commit/?id=ebca1770

Intel-SIG: commit ebca1770 Documentation/admin-guide: Change doc for split_lock_
detect parameter

--------------------------------

Since #DB for bus lock detect changes the split_lock_detect parameter,
update the documentation for the changes.
Signed-off-by: NFenghua Yu <fenghua.yu@intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NTony Luck <tony.luck@intel.com>
Acked-by: NRandy Dunlap <rdunlap@infradead.org>
Link: https://lore.kernel.org/r/20210322135325.682257-4-fenghua.yu@intel.com

(cherry picked from commit ebca1770)
Signed-off-by: NEthan Zhao <haifeng.zhao@linux.intel.com>
Signed-off-by: NJason Zeng <jason.zeng@intel.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -5278,27 +5278,37 @@
 	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 #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"
 			mode.
 
+			#DB exception for bus lock is triggered only when
+			CPL > 0.
+
 	srbds=		[X86,INTEL]
 			Control the Special Register Buffer Data Sampling
 			(SRBDS) mitigation.