linux-kernel - RE: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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Date:   Thu, 12 Dec 2019 19:46:25 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     'Peter Zijlstra' <peterz@...radead.org>,
        'Andy Lutomirski' <luto@...nel.org>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        'Ingo Molnar' <mingo@...nel.org>,
        'Thomas Gleixner' <tglx@...utronix.de>,
        'Ingo Molnar' <mingo@...hat.com>,
        'Borislav Petkov' <bp@...en8.de>,
        'H Peter Anvin' <hpa@...or.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        'linux-kernel' <linux-kernel@...r.kernel.org>,
        'x86' <x86@...nel.org>
Subject: RE: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter

>> If anything we could switch the entire bitmap interface to unsigned int,
>> but I'm not sure that'd actually help much.
>
> As we've been looking for potential split lock issues in kernel code, most of
> the ones we found relate to callers who have <=32 bits and thus stick:
>
>	u32 flags;
>
> in their structure.  So it would solve those places, and fix any future code
> where someone does the same thing.

If different architectures can do better with 8-bit/16-bit/32-bit/64-bit instructions
to manipulate bitmaps, then perhaps this is justification to make all the
functions operate on "bitmap_t" and have each architecture provide the
typedef for their favorite width.

-Tony