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From: Andy Lutomirski <luto@kernel.org>
To: Daniel Axtens <dja@axtens.net>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	 kasan-dev <kasan-dev@googlegroups.com>,
	Linux-MM <linux-mm@kvack.org>, X86 ML <x86@kernel.org>,
	 Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Alexander Potapenko <glider@google.com>,
	 Andrew Lutomirski <luto@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	 Dmitry Vyukov <dvyukov@google.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	 Vasily Gorbik <gor@linux.ibm.com>
Subject: Re: [PATCH v4 1/3] kasan: support backing vmalloc space with real shadow memory
Date: Mon, 19 Aug 2019 15:20:47 -0700	[thread overview]
Message-ID: <CALCETrXnvofB_2KciRL6gZBemtjwTVg4-EKSJx-nz-BULF5aMg@mail.gmail.com> (raw)
In-Reply-To: <87imqtu7pc.fsf@dja-thinkpad.axtens.net>

> On Aug 18, 2019, at 8:58 PM, Daniel Axtens <dja@axtens.net> wrote:
>

>>> Each page of shadow memory represent 8 pages of real memory. Could we use
>>> page_ref to count how many pieces of a shadow page are used so that we can
>>> free it when the ref count decreases to 0.
>
> I'm not sure how much of a difference it will make, but I'll have a look.
>

There are a grand total of eight possible pages that could require a
given shadow page. I would suggest that, instead of reference
counting, you just check all eight pages.

Or, better yet, look at the actual vm_area_struct and are where prev
and next point. That should tell you exactly which range can be freed.


  reply	other threads:[~2019-08-19 22:21 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-15  0:16 [PATCH v4 0/3] kasan: support backing vmalloc space with real shadow memory Daniel Axtens
2019-08-15  0:16 ` [PATCH v4 1/3] " Daniel Axtens
2019-08-16  7:47   ` Christophe Leroy
2019-08-16 17:08     ` Mark Rutland
2019-08-16 17:41       ` Andy Lutomirski
2019-08-19 10:15         ` Mark Rutland
2019-08-19  3:58       ` Daniel Axtens
2019-08-19 22:20         ` Andy Lutomirski [this message]
2019-08-15  0:16 ` [PATCH v4 2/3] fork: support VMAP_STACK with KASAN_VMALLOC Daniel Axtens
2019-08-15  0:16 ` [PATCH v4 3/3] x86/kasan: support KASAN_VMALLOC Daniel Axtens
2019-08-16  8:04   ` Christophe Leroy
2019-08-15 11:28 ` [PATCH v4 0/3] kasan: support backing vmalloc space with real shadow memory Mark Rutland

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