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From:   Marco Elver <elver@google.com>
Date:   Mon, 28 Sep 2020 13:53:55 +0200
Message-ID: <CANpmjNMS-6mfDF6o31yiejP0wmgpEeuoh0PP9QJa-qt0OpiRBg@mail.gmail.com>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64
To:     Will Deacon <will@kernel.org>,
        Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     "H. Peter Anvin" <hpa@zytor.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoph Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hillf Danton <hdanton@sina.com>,
        Ingo Molnar <mingo@redhat.com>, Jann Horn <jannh@google.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        SeongJae Park <sjpark@amazon.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vlastimil Babka <vbabka@suse.cz>,
        "the arch/x86 maintainers" <x86@kernel.org>,
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        Linux Memory Management List <linux-mm@kvack.org>
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On Mon, 21 Sep 2020 at 16:31, Will Deacon <will@kernel.org> wrote:
> On Mon, Sep 21, 2020 at 03:26:04PM +0200, Marco Elver wrote:
> > Add architecture specific implementation details for KFENCE and enable
> > KFENCE for the arm64 architecture. In particular, this implements the
> > required interface in <asm/kfence.h>. Currently, the arm64 version does
> > not yet use a statically allocated memory pool, at the cost of a pointer
> > load for each is_kfence_address().
[...]
> > For ARM64, we would like to solicit feedback on what the best option is
> > to obtain a constant address for __kfence_pool. One option is to declare
> > a memory range in the memory layout to be dedicated to KFENCE (like is
> > done for KASAN), however, it is unclear if this is the best available
> > option. We would like to avoid touching the memory layout.

> Given that the pool is relatively small (i.e. when compared with our virtual
> address space), dedicating an area of virtual space sounds like it makes
> the most sense here. How early do you need it to be available?

Note: we're going to send a v4 this or next week with a few other
minor fixes in it. But I think we just don't want to block the entire
series on figuring out what the static-pool arm64 version should do,
especially if we'll have a few iterations with only this patch here
changing.

So the plan will be:

1. Send v4, which could from our point-of-view be picked up for
merging. Unless of course there are more comments.

2. Work out the details for the static-pool arm64 version, since it
doesn't seem trivial to do the same thing as we do for x86. In
preparation for that, v4 will allow the __kfence_pool's attributes to
be defined entirely by <asm/kfence.h>, so that we can fiddle with
sections etc.

3. Send patch switching out the simpler arm64 version here for one
that places __kfence_pool at a static location.

Hopefully that plan is reasonable.

Thanks,
-- Marco