linux-kernel - Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

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Date:   Thu, 15 Oct 2020 14:39:48 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Marco Elver <elver@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christoph Lameter <cl@...ux.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hillf Danton <hdanton@...a.com>,
        Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        SeongJae Park <sjpark@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>,
        the arch/x86 maintainers <x86@...nel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64

On Wed, Oct 14, 2020 at 09:12:37PM +0200, Marco Elver wrote:
> On Thu, 8 Oct 2020 at 12:45, Mark Rutland <mark.rutland@....com> wrote:
> > On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote:
> > > On Thu, 1 Oct 2020 at 19:58, Mark Rutland <mark.rutland@....com> wrote:

> > > > > > If you need virt_to_page() to work, the address has to be part of the
> > > > > > linear/direct map.

> > > We're going with dynamically allocating the pool (for both x86 and
> > > arm64), 

[...]

> We've got most of this sorted now for v5 -- thank you!
> 
> The only thing we're wondering now, is if there are any corner cases
> with using memblock_alloc'd memory for the KFENCE pool? (We'd like to
> avoid page alloc's MAX_ORDER limit.) We have a version that passes
> tests on x86 and arm64, but checking just in case. :-)

AFAICT otherwise the only noticeable difference might be PageSlab(), if
that's clear for KFENCE allocated pages? A few helpers appear to check
that to determine how something was allocated (e.g. in the scatterlist
and hwpoison code), and I suspect that needs to behave the same.

Otherwise, I *think* using memblock_alloc should be fine on arm64; I'm
not entirely sure for x86 (but suspect it's similar). On arm64:

* All memory is given a struct page via memblocks_present() adding all
  memory memblocks. This includes memory allocated by memblock_alloc().

* All memory is mapped into the linear map via arm64's map_mem() adding
  all (non-nomap) memory memblocks. This includes memory allocated by
  memblock_alloc().

Thanks,
Mark.