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Date:   Fri, 11 Mar 2022 10:37:16 +0000
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Lecopzer Chen <lecopzer.chen@mediatek.com>,
        Arnd Bergmann <arnd@arndb.de>, linux-kernel@vger.kernel.org,
        andreyknvl@gmail.com, anshuman.khandual@arm.com, ardb@kernel.org,
        dvyukov@google.com, geert+renesas@glider.be, glider@google.com,
        kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org,
        lukas.bulwahn@gmail.com, mark.rutland@arm.com,
        masahiroy@kernel.org, matthias.bgg@gmail.com,
        ryabinin.a.a@gmail.com, yj.chiang@mediatek.com
Subject: Re: [PATCH v3 0/2] arm: kasan: support CONFIG_KASAN_VMALLOC
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On Fri, Mar 11, 2022 at 12:08:52AM +0100, Linus Walleij wrote:
> On Sun, Feb 27, 2022 at 2:48 PM Lecopzer Chen
> <lecopzer.chen@mediatek.com> wrote:
> 
> > Since the framework of KASAN_VMALLOC is well-developed,
> > It's easy to support for ARM that simply not to map shadow of VMALLOC
> > area on kasan_init.
> >
> > Since the virtual address of vmalloc for Arm is also between
> > MODULE_VADDR and 0x100000000 (ZONE_HIGHMEM), which means the shadow
> > address has already included between KASAN_SHADOW_START and
> > KASAN_SHADOW_END.
> > Thus we need to change nothing for memory map of Arm.
> >
> > This can fix ARM_MODULE_PLTS with KASan, support KASan for higmem
> > and provide the first step to support CONFIG_VMAP_STACK with Arm.
> >
> >
> > Test on
> > 1. Qemu with memory 2G and vmalloc=500M for 3G/1G mapping.
> > 2. Qemu with memory 2G and vmalloc=500M for 3G/1G mapping + LPAE.
> > 3. Qemu with memory 2G and vmalloc=500M for 2G/2G mapping.
> >
> > v3:
> >     rebase on 5.17-rc5.
> >     Add simple doc for "arm: kasan: support CONFIG_KASAN_VMALLOC"
> >     Tweak commit message.
> 
> Ater testing this with my kernel-in-vmalloc patches and some hacks, I got
> the kernel booting in the VMALLOC area with KASan enabled!
> See:
> https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/log/?h=kernel-in-vmalloc-v5.17-rc1
> 
> That's a pretty serious stress test. So:
> Tested-by: Linus Walleij <linus.walleij@linaro.org>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> for the series.
> 
> I suppose you could put this into Russell's patch tracker, it's gonna be
> for kernel v5.19 by now but why stress. It seems I can fix up
> kernel-in-vmalloc on top and submit that for v5.19 as well.

Ard's series already adds vmap stack support (which we've been doing
some last minute panic-debugging on to get it ready for this merge
window), but the above description makes it sound like this series is
a pre-requisit for that.

Is it? Will Ard's work cause further regressions because this series
isn't merged.

Please clarify - and urgently, there is not much time left before the
merge window opens.

-- 
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