linux-kernel - Re: [PATCH v2 12/33] kmsan: Allow disabling KMSAN checks for the current task

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Date:   Mon, 11 Dec 2023 12:50:22 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v2 12/33] kmsan: Allow disabling KMSAN checks for the
 current task

On Tue, Nov 21, 2023 at 11:06 PM Ilya Leoshkevich <iii@...ux.ibm.com> wrote:
>
> Like for KASAN, it's useful to temporarily disable KMSAN checks around,
> e.g., redzone accesses. Introduce kmsan_disable_current() and
> kmsan_enable_current(), which are similar to their KASAN counterparts.

Initially we used to have this disablement counter in KMSAN, but
adding it uncontrollably can result in KMSAN not functioning properly.
E.g. forgetting to call kmsan_disable_current() or underflowing the
counter will break reporting.
We'd better put this API in include/linux/kmsan.h to indicate it
should be discouraged.

> Even though it's not strictly necessary, make them reentrant, in order
> to match the KASAN behavior.

Until this becomes strictly necessary, I think we'd better
KMSAN_WARN_ON if the counter is re-entered.