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Date:   Thu, 21 Nov 2019 07:04:44 +0100
From:   Ingo Molnar <mingo@kernel.org>
To:     Fenghua Yu <fenghua.yu@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        H Peter Anvin <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Tony Luck <tony.luck@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        linux-kernel <linux-kernel@vger.kernel.org>, x86 <x86@kernel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter
Message-ID: <20191121060444.GA55272@gmail.com>
References: <1574297603-198156-1-git-send-email-fenghua.yu@intel.com>
 <1574297603-198156-7-git-send-email-fenghua.yu@intel.com>
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* Fenghua Yu <fenghua.yu@intel.com> wrote:

> Split lock detection is disabled by default. Enable the feature by
> kernel parameter "split_lock_detect".
> 
> Usually it is enabled in real time when expensive split lock issues
> cannot be tolerated so should be fatal errors, or for debugging and
> fixing the split lock issues to improve performance.
> 
> Please note: enabling this feature will cause kernel panic or SIGBUS
> to user application when a split lock issue is detected.
> 
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
>  .../admin-guide/kernel-parameters.txt         | 10 ++++++
>  arch/x86/kernel/cpu/intel.c                   | 34 +++++++++++++++++++
>  2 files changed, 44 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8dee8f68fe15..1ed313891f44 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3166,6 +3166,16 @@
>  
>  	nosoftlockup	[KNL] Disable the soft-lockup detector.
>  
> +	split_lock_detect
> +			[X86] Enable split lock detection
> +			This is a real time or debugging feature. When enabled
> +			(and if hardware support is present), atomic
> +			instructions that access data across cache line
> +			boundaries will result in an alignment check exception.
> +			When triggered in applications the kernel will send
> +			SIGBUS. The kernel will panic for a split lock in
> +			OS code.

It would be really nice to be able to enable/disable this runtime as 
well, has this been raised before, and what was the conclusion?

Thanks,

	Ingo