Re: [PATCH v5 3/3] Documentation/admin-guide: Change doc for split_lock_detect parameter

[Thomas Gleixner]

On Sat, Mar 13 2021 at 05:49, Fenghua Yu wrote:
> + ratelimit:N -
> +   Set rate limit to N bus locks per second
> +   for bus lock detection. 0 < N.
> +   Only applied to non-root users.

Of course this does not mention that the limit is per UID and it neither
tells what the action is to rate limit the bus lock attempts. The rate
limit saturation which is induced by msleep() is not mentioned either.

Really useful for administrators.

Thanks,

tglx

[PATCH v5 3/3] Documentation/admin-guide: Change doc for split_lock_detect parameter

[Fenghua Yu]

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

Signed-off-by: Fenghua Yu 
Reviewed-by: Tony Luck 
Acked-by: Randy Dunlap 
---
Change Log:
v5:
- Remove N < HZ/2 check info in the doc (Thomas).

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 04545725f187..16b2e1c45d04 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5100,27 +5100,45 @@
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.
+ 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.
-- 
2.30.2