linux-kernel - Re: [PATCH -next 0/3] replace open coded VA->PA calculation

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Message-ID: <CACRpkdaNv7850mOyXRMgmPf8TQxiM-C5VEkGnLfd+wvffW8FAg@mail.gmail.com>
Date:   Wed, 22 Dec 2021 03:31:10 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     cuigaosheng <cuigaosheng1@...wei.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Andrew Lunn <andrew@...n.ch>,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Shiraz Hashim <shiraz.linux.kernel@...il.com>,
        SoC Team <soc@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/SAMSUNG EXYNOS ARM ARCHITECTURES" 
        <linux-samsung-soc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        gongruiqi1@...wei.com, wangweiyang2@...wei.com
Subject: Re: [PATCH -next 0/3] replace open coded VA->PA calculation

On Tue, Dec 21, 2021 at 10:16 AM Arnd Bergmann <arnd@...db.de> wrote:

> I think for CPUs that can use LPAE, we want to eventually move to the 4G:4G
> memory model, which in turn depends on having the kernel in vmalloc space, as
> implemented by Linus Walleij in
> https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-integrator.git/log/?h=kernel-in-vmalloc-v5.14-rc1

Yeah I'm still working on this series. The 4/4 split works pretty well,
but it breaks KASan and I was in the process of fixing that when I left
for parental leave.

The reason it breaks would be related to KASan not expecting
executable code in the vmalloc area, and since the shadowing
algorithm is a simple pointer offset, and since we go to lengths
to chisel shadow memory out of lowmem at a fixed offset from
TEXT_OFFSET, we have a problem.

The patch "KASAN horror" shows what I am trying to do to fix it,
it's "just" some hard work missing.

Yours,
Linus Walleij