linux-kernel - Re: [PATCH 0/4] ARM: Support KFENCE feature

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Message-ID: <YSYiEgEcW1Ln3+9P@elver.google.com>
Date:   Wed, 25 Aug 2021 12:57:22 +0200
From:   Marco Elver <elver@...gle.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] ARM: Support KFENCE feature

On Wed, Aug 25, 2021 at 12:14PM +0200, Marco Elver wrote:
> On Wed, 25 Aug 2021 at 11:17, Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> > The patch 1~3 is to support KFENCE feature on ARM.
> >
> > NOTE:
> > The context of patch2/3 changes in arch/arm/mm/fault.c is based on link[1],
> > which make some refactor and cleanup about page fault.
> >
> > kfence_test is not useful when kfence is not enabled, skip kfence test
> > when kfence not enabled in patch4.
> >
> > I tested the kfence_test on ARM QEMU with or without ARM_LPAE and all passed.
> 
> Thank you for enabling KFENCE on ARM -- I'll leave arch-code review to
> an ARM maintainer.
> 
> However, as said on the patch, please drop the change to the
> kfence_test and associated changes. This is working as intended; while
> you claim that it takes a long time to run when disabled, when running
> manually you just should not run it when disabled. There are CI
> systems that rely on the KUnit test output and the fact that the
> various test cases say "not ok" etc. Changing that would mean such CI
> systems would no longer fail if KFENCE was accidentally disabled (once
> KFENCE is enabled on various CI, which we'd like to do at some point).
> There are ways to fail the test faster, but they all complicate the
> test for no good reason. (And the addition of a new exported function
> that is essentially useless.)

I spoke too soon -- we export __kfence_pool, and that's good enough to
fail the test fast if KFENCE was disabled at boot:

	https://lkml.kernel.org/r/20210825105533.1247922-1-elver@google.com

will do the trick. So please drop your patch 4/4 here.

Thanks,
-- Marco