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SubjectRe: [tip: x86/splitlock] Documentation/x86: Add buslock.rst
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On 5/18/2021 10:44 PM, tip-bot2 for Fenghua Yu wrote:
...
> +
> +Software handling
> +=================
> +
> +The kernel #AC and #DB handlers handle bus lock based on the kernel
> +parameter "split_lock_detect". Here is a summary of different options:
> +
> ++------------------+----------------------------+-----------------------+
> +|split_lock_detect=|#AC for split lock |#DB for bus lock |
> ++------------------+----------------------------+-----------------------+
> +|off |Do nothing |Do nothing |
> ++------------------+----------------------------+-----------------------+
> +|warn |Kernel OOPs |Warn once per task and |
> +|(default) |Warn once per task and |and continues to run. |
> +| |disable future checking | |
> +| |When both features are | |
> +| |supported, warn in #AC | |
> ++------------------+----------------------------+-----------------------+
> +|fatal |Kernel OOPs |Send SIGBUS to user. |
> +| |Send SIGBUS to user | |
> +| |When both features are | |
> +| |supported, fatal in #AC | |
> ++------------------+----------------------------+-----------------------+
> +

Hi all,

I'm wonder if using only one "split_lock_detect" parameter for those two
features is good/correct.

In fact, split lock is just one type of bus lock. There are two types
bus lock:
1) split lock, lock on WB memory across multiple cache lines;
2) lock on non-WB memory;

As current design, if both features are available, it only enables #AC
for split lock either for "warn" or "fatal". Thus we cannot capture any
bus lock due to 2) lock on non-WB memory.

Why not provide separate parameter for them? e.g., split_lock_detect and
bus_lock_detect. Then they can be configured and enabled independently.

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