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

From: Marco Elver <elver@google.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Potapenko <glider@google.com>,
	Will Deacon <will@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"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>,
	Dmitriy Vyukov <dvyukov@google.com>,
	Eric Dumazet <edumazet@google.com>,
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	Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64
Date: Thu, 15 Oct 2020 16:15:03 +0200	[thread overview]
Message-ID: <CANpmjNO9Gw0-U+QynFWPPZYEVgnZA84VHi_XrXfa5aiAq3kPuQ@mail.gmail.com> (raw)
In-Reply-To: <20201015133948.GB50416@C02TD0UTHF1T.local>

On Thu, 15 Oct 2020 at 15:39, Mark Rutland <mark.rutland@arm.com> wrote:
> 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.

We had to take care of setting PageSlab before, too. We do this during
kfence_init().

> 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().

Very good, thank you. We'll send v5 with these changes rebased on
5.10-rc1 (in ~2 weeks).

Thanks,
-- Marco