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In-Reply-To: <CANpmjNPsBa=8+Ned03LW_0qUsM6fy-E51dpFKm8ok-vcMQGMmA@mail.gmail.com>
From:   Peter Collingbourne <pcc@google.com>
Date:   Thu, 9 Dec 2021 14:12:03 -0800
Message-ID: <CAMn1gO4=8ovgRs5fpmP_4d-xqEXsR32SWHJT8YmXwZGmdWyfbg@mail.gmail.com>
Subject: Re: [PATCH v3 0/6] kernel: introduce uaccess logging
To:     Marco Elver <elver@google.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andy Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Sami Tolvanen <samitolvanen@google.com>,
        YiFei Zhu <yifeifz2@illinois.edu>,
        Mark Rutland <mark.rutland@arm.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Gabriel Krisman Bertazi <krisman@collabora.com>,
        Chris Hyser <chris.hyser@oracle.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Arnd Bergmann <arnd@arndb.de>,
        Dmitry Vyukov <dvyukov@google.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Alexey Gladkov <legion@kernel.org>,
        Ran Xiaokai <ran.xiaokai@zte.com.cn>,
        David Hildenbrand <david@redhat.com>,
        Xiaofeng Cao <caoxiaofeng@yulong.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Thomas Cedeno <thomascedeno@google.com>,
        Alexander Potapenko <glider@google.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Evgenii Stepanov <eugenis@google.com>
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On Wed, Dec 8, 2021 at 7:33 AM Marco Elver <elver@google.com> wrote:
>
> On Wed, 8 Dec 2021 at 05:48, Peter Collingbourne <pcc@google.com> wrote:
> [...]
> > Peter Collingbourne (6):
> >   include: split out uaccess instrumentation into a separate header
> >   uaccess-buffer: add core code
> >   fs: use copy_from_user_nolog() to copy mount() data
> >   uaccess-buffer: add CONFIG_GENERIC_ENTRY support
> >   arm64: add support for uaccess logging
> >   Documentation: document uaccess logging
>
> I think it needs to be possible to disable the feature via a Kconfig
> option. Not all systems want or could even tolerate the additional
> overheads -- even though you say they are minimal elsewhere. For
> example, some embedded systems most likely have absolutely no use for
> this feature, and the increase in .text might be unacceptable. Certain
> features that we usually take for granted are no different (see
> init/Kconfig: FUTEX, EPOLL, .. etc). If you'd like it enabled by
> default, given the overheads are small enough, it can do "default y"
> and be configurable only "if EXPERT".

Okay, done.

> Is it possible to add a kselftest-style test to
> tools/testing/selftests? In addition to the basic tests, can certain
> non-trivial properties, like masking of signals, also be tested? I
> think that'd be extremely valuable, because I'm sure we'd have to
> backport this to several older kernels.

Yes, I've added a new patch with a kselftest. (Good thing I did,
because it (together with DEBUG_PREEMPT) uncovered a bug in the
pre/post-exit-loop code. Fixed in v4.)

Peter