linux-kernel - Re: [PATCH RFC v3 4/4] Documentation/admin-guide: Change doc for split_lock

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Date:   Fri, 30 Oct 2020 20:14:15 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH RFC v3 4/4] Documentation/admin-guide: Change doc for
 split_lock_detect parameter

Hi,

On 10/30/20 5:27 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@...el.com>
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> ---
> Change Log:
> - Simplify the documentation (Randy).
> 
>  .../admin-guide/kernel-parameters.txt         | 28 +++++++++++++++----
>  1 file changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 526d65d8573a..ee419ce659f5 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5044,27 +5044,45 @@
>  	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

				                       rate-limited

>  				  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 supports split lock

				                           support

> +				  detection or bus lock detection. Default
> +				  behavior is from #DB if both features are

I would say			           is by #DB

> +				  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 from #AC

and				                              is by #AC

> +				  if both features are enabled in hardware.
> +
> +			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

				                                    non-root

> +				  user.

				  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.
> +

thanks.
-- 
~Randy