From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Joonsoo Kim <js1304@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexander Potapenko <glider@google.com>,
kasan-dev <kasan-dev@googlegroups.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
kernel-team@lge.com
Subject: Re: [PATCH v1 00/11] mm/kasan: support per-page shadow memory to reduce memory consumption
Date: Tue, 30 May 2017 10:08:21 +0100 [thread overview]
Message-ID: <35288874-d800-f534-13bf-4261167ff1bd@arm.com> (raw)
In-Reply-To: <CACT4Y+YkEMPe3uZmPO+HmpAk6JckdiGhxWq=7i8t2WG2efZgZw@mail.gmail.com>
On 30/05/17 09:49, Dmitry Vyukov wrote:
> On Tue, May 30, 2017 at 10:40 AM, Vladimir Murzin
> <vladimir.murzin@arm.com> wrote:
>> On 30/05/17 09:31, Vladimir Murzin wrote:
>>> [This sender failed our fraud detection checks and may not be who they appear to be. Learn about spoofing at http://aka.ms/LearnAboutSpoofing]
>>>
>>> On 30/05/17 09:15, Dmitry Vyukov wrote:
>>>> On Tue, May 30, 2017 at 9:58 AM, Vladimir Murzin
>>>> <vladimir.murzin@arm.com> wrote:
>>>>> On 29/05/17 16:29, Dmitry Vyukov wrote:
>>>>>> I have an alternative proposal. It should be conceptually simpler and
>>>>>> also less arch-dependent. But I don't know if I miss something
>>>>>> important that will render it non working.
>>>>>> Namely, we add a pointer to shadow to the page struct. Then, create a
>>>>>> slab allocator for 512B shadow blocks. Then, attach/detach these
>>>>>> shadow blocks to page structs as necessary. It should lead to even
>>>>>> smaller memory consumption because we won't need a whole shadow page
>>>>>> when only 1 out of 8 corresponding kernel pages are used (we will need
>>>>>> just a single 512B block). I guess with some fragmentation we need
>>>>>> lots of excessive shadow with the current proposed patch.
>>>>>> This does not depend on TLB in any way and does not require hooking
>>>>>> into buddy allocator.
>>>>>> The main downside is that we will need to be careful to not assume
>>>>>> that shadow is continuous. In particular this means that this mode
>>>>>> will work only with outline instrumentation and will need some ifdefs.
>>>>>> Also it will be slower due to the additional indirection when
>>>>>> accessing shadow, but that's meant as "small but slow" mode as far as
>>>>>> I understand.
>>>>>>
>>>>>> But the main win as I see it is that that's basically complete support
>>>>>> for 32-bit arches. People do ask about arm32 support:
>>>>>> https://groups.google.com/d/msg/kasan-dev/Sk6BsSPMRRc/Gqh4oD_wAAAJ
>>>>>> https://groups.google.com/d/msg/kasan-dev/B22vOFp-QWg/EVJPbrsgAgAJ
>>>>>> and probably mips32 is relevant as well.
>>>>>> Such mode does not require a huge continuous address space range, has
>>>>>> minimal memory consumption and requires minimal arch-dependent code.
>>>>>> Works only with outline instrumentation, but I think that's a
>>>>>> reasonable compromise.
>>>>>
>>>>> .. or you can just keep shadow in page extension. It was suggested back in
>>>>> 2015 [1], but seems that lack of stack instrumentation was "no-way"...
>>>>>
>>>>> [1] https://lkml.org/lkml/2015/8/24/573
>>>>
>>>> Right. It describes basically the same idea.
>>>>
>>>> How is page_ext better than adding data page struct?
>>>
>>> page_ext is already here along with some other debug options ;)
>
>
> But page struct is also here. What am I missing?
>
Probably, free room in page struct? I guess most of the page_ext stuff would
love to live in page struct, but... for instance, look at page idle tracking
which has to live in page_ext only for 32-bit.
>
>>>> It seems that memory for all page_ext is preallocated along with page
>>>> structs; but just the lookup is slower.
>>>>
>>>
>>> Yup. Lookup would look like (based on v4.0):
>>>
>>> ...
>>> page_ext = lookup_page_ext_begin(virt_to_page(start));
>>>
>>> do {
>>> page_ext->shadow[idx++] = value;
>>> } while (idx < bound);
>>>
>>> lookup_page_ext_end((void *)page_ext);
>>>
>>> ...
>>
>> Correction: please, ignore that *_{begin,end} stuff - mainline only
>> lookup_page_ext() is only used.
>
>
> Note that this added code will be executed during handling of each and
> every memory access in kernel. Every instruction matters on that path.
I know, I know... still better than nothing.
> The additional indirection via page struct will also slow down it, but
> that's the cost for lower memory consumption and potentially 32-bit
> support. For page_ext it looks like even more overhead for no gain.
>
eefa864 (mm/page_ext: resurrect struct page extending code for debugging)
express some cases where keeping data in page_ext has benefit.
Cheers
Vladimir
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next prev parent reply other threads:[~2017-05-30 9:08 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-16 1:16 [PATCH v1 00/11] mm/kasan: support per-page shadow memory to reduce memory consumption js1304
2017-05-16 1:16 ` [PATCH v1 01/11] mm/kasan: rename XXX_is_zero to XXX_is_nonzero js1304
2017-05-16 1:16 ` [PATCH v1 02/11] mm/kasan: don't fetch the next shadow value speculartively js1304
2017-05-16 1:16 ` [PATCH v1 03/11] mm/kasan: handle unaligned end address in zero_pte_populate js1304
2017-05-16 1:16 ` [PATCH v1 04/11] mm/kasan: extend kasan_populate_zero_shadow() js1304
2017-05-16 1:16 ` [PATCH v1 05/11] mm/kasan: introduce per-page shadow memory infrastructure js1304
2017-05-16 1:16 ` [PATCH v1 06/11] mm/kasan: mark/unmark the target range that is for original shadow memory js1304
2017-05-16 1:16 ` [PATCH v1 07/11] x86/kasan: use per-page " js1304
2017-05-16 1:16 ` [PATCH v1 08/11] mm/kasan: support on-demand shadow allocation/mapping js1304
2017-05-16 1:16 ` [PATCH v1 09/11] x86/kasan: support on-demand shadow mapping js1304
2017-05-16 1:16 ` [PATCH v1 10/11] mm/kasan: support dynamic shadow memory free js1304
2017-05-16 1:16 ` [PATCH v1 11/11] mm/kasan: change the order of shadow memory check js1304
2017-05-16 1:28 ` [PATCH(RE-RESEND) v1 01/11] mm/kasan: rename _is_zero to _is_nonzero Joonsoo Kim
2017-05-16 4:34 ` [PATCH v1 00/11] mm/kasan: support per-page shadow memory to reduce memory consumption Dmitry Vyukov
2017-05-16 4:47 ` Dmitry Vyukov
2017-05-16 6:23 ` Joonsoo Kim
2017-05-16 20:49 ` Dmitry Vyukov
2017-05-17 7:23 ` Joonsoo Kim
2017-05-17 7:25 ` Joonsoo Kim
2017-05-24 6:57 ` Dmitry Vyukov
2017-05-24 7:45 ` Joonsoo Kim
2017-05-24 17:19 ` Dmitry Vyukov
2017-05-25 0:41 ` Joonsoo Kim
2017-05-29 15:07 ` Dmitry Vyukov
2017-05-29 15:12 ` Dmitry Vyukov
2017-05-29 15:29 ` Dmitry Vyukov
2017-05-30 7:58 ` Vladimir Murzin
2017-05-30 8:15 ` Dmitry Vyukov
2017-05-30 8:31 ` Vladimir Murzin
2017-05-30 8:40 ` Vladimir Murzin
2017-05-30 8:49 ` Dmitry Vyukov
2017-05-30 9:08 ` Vladimir Murzin [this message]
2017-05-30 9:26 ` Dmitry Vyukov
2017-05-30 9:39 ` Vladimir Murzin
2017-05-30 9:45 ` Dmitry Vyukov
2017-05-30 9:54 ` Vladimir Murzin
2017-05-30 14:16 ` Andrey Ryabinin
2017-05-31 5:50 ` Joonsoo Kim
2017-05-31 16:31 ` Andrey Ryabinin
2017-06-08 2:43 ` Joonsoo Kim
2017-06-01 15:16 ` 王靖天
2017-06-01 18:06 ` Dmitry Vyukov
2017-06-08 2:40 ` Joonsoo Kim
2017-06-13 16:49 ` Andrey Ryabinin
2017-06-14 0:12 ` Joonsoo Kim
2017-05-17 12:17 ` Andrey Ryabinin
2017-05-19 1:53 ` Joonsoo Kim
2017-05-22 6:02 ` Dmitry Vyukov
2017-05-24 6:04 ` Joonsoo Kim
2017-05-24 16:31 ` Dmitry Vyukov
2017-05-25 0:46 ` Joonsoo Kim
2017-05-22 14:00 ` Andrey Ryabinin
2017-05-24 6:18 ` Joonsoo Kim
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