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

From: Mark Rutland <mark.rutland@arm.com>
To: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>,
	Will Deacon <will@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
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	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>,
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Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64
Date: Thu, 15 Oct 2020 14:39:48 +0100	[thread overview]
Message-ID: <20201015133948.GB50416@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CANpmjNOg2OeWpXn57_ikqv4KR0xVEooCDECUyRijgr0tt4+Ncw@mail.gmail.com>

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@arm.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@arm.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.