linux-kernel - Re: [PATCH v1 00/11] mm/kasan: support per-page shadow memory to reduce memory consumption

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Message-ID: <20170608024303.GC27998@js1304-desktop>
Date:   Thu, 8 Jun 2017 11:43:05 +0900
From:   Joonsoo Kim <js1304@...il.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, kernel-team@....com
Subject: Re: [PATCH v1 00/11] mm/kasan: support per-page shadow memory to
 reduce memory consumption

On Wed, May 31, 2017 at 07:31:53PM +0300, Andrey Ryabinin wrote:
> On 05/31/2017 08:50 AM, Joonsoo Kim wrote:
> >>> 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.
> >>
> >> I don't see how above is relevant for 32-bit arches. Current design
> >> is perfectly fine for 32-bit arches. I did some POC arm32 port couple years
> >> ago - https://github.com/aryabinin/linux/commits/kasan/arm_v0_1
> >> It has some ugly hacks and non-critical bugs. AFAIR it also super-slow because I (mistakenly) 
> >> made shadow memory uncached. But otherwise it works.
> > 
> > Could you explain that where is the code to map shadow memory uncached?
> > I don't find anything related to it.
> > 
> 
> I didn't set set any cache policy (L_PTE_MT_*) on shadow mapping (see set_pte_at() calls )
> which means it's L_PTE_MT_UNCACHED 

Thanks for pointing it out.

I did some quick tests and found that it's not super(?) slow on my
QEMU. Maybe, it would be different with real machine.

Thanks.