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Date: Fri, 1 Jul 2022 11:16:53 +0200
From: Vincent Whitchurch <vincent.whitchurch@axis.com>
Subject: Re: [PATCH v4 2/2] UML: add support for KASAN under x86_64
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To: David Gow <davidgow@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>, Dmitry Vyukov <dvyukov@google.com>, Johannes Berg <johannes@sipsolutions.net>, Patricia Alfonso <trishalfonso@google.com>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, "anton.ivanov@cambridgegreys.com" <anton.ivanov@cambridgegreys.com>, Brendan Higgins <brendanhiggins@google.com>, Andrew Morton <akpm@linux-foundation.org>, Andrey Ryabinin <ryabinin.a.a@gmail.com>, kasan-dev <kasan-dev@googlegroups.com>, "linux-um@lists.infradead.org" <linux-um@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, Daniel Latypov <dlatypov@google.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "kunit-dev@googlegroups.com" <kunit-dev@googlegroups.com>

On Fri, Jul 01, 2022 at 11:08:27AM +0200, David Gow wrote:
> On Thu, Jun 30, 2022 at 9:29 PM Andrey Konovalov <andreyknvl@gmail.com> wrote:
> > Stack trace collection code might trigger KASAN splats when walking
> > stack frames, but this can be resolved by using unchecked accesses.
> > The main reason to disable instrumentation here is for performance
> > reasons, see the upcoming patch for arm64 [1] for some details.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=802b91118d11
> 
> Ah -- that does it! Using READ_ONCE_NOCHECK() in dump_trace() gets rid
> of the nasty recursive KASAN failures we were getting in the tests.
> 
> I'll send out v5 with those files instrumented again.

Hmm, do we really want that?  In the patch Andrey linked to above he
removed the READ_ONCE_NOCHECK() and added the KASAN_SANITIZE on the
corresponding files for arm64, just like it's already the case in this
patch for UML.

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