linux-kernel - Re: ARM: static kernel in vmalloc space

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Message-ID: <CAK8P3a1DQWG1+ab2+vQ2XCAKYxPUjJk5g3W3094j-adDXSQfzQ@mail.gmail.com>
Date:   Tue, 12 May 2020 21:49:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     afzal mohammed <afzal.mohd.ma@...il.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: ARM: static kernel in vmalloc space

On Tue, May 12, 2020 at 12:48 PM afzal mohammed <afzal.mohd.ma@...il.com> wrote:
>
> On Mon, May 11, 2020 at 05:29:29PM +0200, Arnd Bergmann wrote:
>
> > What do you currently do with the module address space?
>
> In the current setup, module address space was untouched, i.e. virtual
> address difference b/n text & module space is far greater than 32MB, at
> least > (2+768+16)MB and modules can't be loaded unless ARM_MODULE_PLTS
> is enabled (this was checked now)
>
> > easiest way is to just always put modules into vmalloc space, as we already
> > do with CONFIG_ARM_MODULE_PLTS when the special area gets full,
> > but that could be optimized once the rest works.
>
> Okay

Any idea which bit you want to try next? Creating a raw_copy_{from,to}_user()
based on get_user_pages()/kmap_atomic()/memcpy() is probably a good
next thing to do. I think it can be done one page at a time with only
checking for
get_fs(), access_ok(), and page permissions, while get_user()/put_user()
need to handle a few more corner cases.

        Arnd