linux-kernel - RE: [PATCH v2 1/2] x86/split_lock: Make life miserable for split lockers

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Date:   Thu, 17 Mar 2022 22:40:16 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Thomas Gleixner' <tglx@...utronix.de>,
        Pavel Machek <pavel@...x.de>
CC:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH v2 1/2] x86/split_lock: Make life miserable for split
 lockers

> They are actually more likely to happen in the kernel
> when code casts int[] to long[] and then uses the 'BIT' functions to
> set/clear bits - which do locked operations.
> Quite often then don't need the locks anyway.
> And that cast is surprisingly common and completely broken on BE.

Default split lock mode is "kernel dies". We had to fix up a dozen or
so places (mostly involving set_bit/clr_bit as you describe). But
all Ice Lake. Tiger Lake and Alder Lake systems are running in
that mode ... and we haven't heard of widespread death (or disabling
the boot option).

-Tony