Re: [PATCH RFC v2 4/4] Documentation: Change doc for split_lock_detect parameter

[Randy Dunlap]

On 10/28/20 1:28 PM, Fenghua Yu wrote:
> 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@xxxxxxxxx>
> Reviewed-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
>  .../admin-guide/kernel-parameters.txt         | 47 +++++++++++++++----
>  1 file changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 526d65d8573a..51312484c2b6 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5044,27 +5044,58 @@
>  	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 an debug exception for
> +			bus lock detection.
>  
>  			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.
> +			warn	- Default mode.
>  
> -			fatal	- the kernel will send SIGBUS to applications
> -				  that trigger the #AC exception.
> +				  If split lock detection is enabled in
> +				  hardware, the kernel will emit rate limited
> +				  warnings about applications triggering the #AC
> +				  exception.
> +
> +				  If bus lock detection is enabled in hardware,
> +				  the kernel will emit rate limited warnings
> +				  about applications triggering the #DB
> +				  exception.
> +
> +				  Default behavior is from bus lock detection
> +				  if both features are enabled in hardware.
> +
> +			fatal	- If split lock detection is enabled in
> +				  hardware, the kernel will send SIGBUS to
> +				  applications that trigger the #AC exception.
> +
> +				  If bus lock detection is enabled in hardware,
> +				  the kernel will send SIGBUS to application
> +				  that trigger the #DB exception.
> +
> +				  Default behavior is from split lock detection
> +				  if both are enabled in hardware.
> +

Hi,
This appears to have quite a bit of duplicated lines....

> +			ratelimit:N
> +				  Set rate limit to N bus locks per second
> +				  for bus lock detection. 0 < N <= HZ/2 and
> +				  N is approximate. Only applied to non root
> +				  user.
> +
> +				  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.
> 


-- 
~Randy