linux-kernel - Re: [PATCH] MIPS: Handle address errors for accesses above CPU max virtual user address

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Message-ID: <CAK8P3a16UjuM0Dz-ERahAfzkAD9D7Cc3sd3yT_e7cVio=qvgPA@mail.gmail.com>
Date:   Tue, 22 Feb 2022 22:42:22 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     linux-mips <linux-mips@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: Handle address errors for accesses above CPU max
 virtual user address

On Tue, Feb 22, 2022 at 8:58 PM Thomas Bogendoerfer
<tsbogend@...ha.franken.de> wrote:
>
> On Tue, Feb 22, 2022 at 06:04:07PM +0100, Arnd Bergmann wrote:
> > On Tue, Feb 22, 2022 at 4:53 PM Thomas Bogendoerfer
> > <tsbogend@...ha.franken.de> wrote:
> > >
> > > Address errors have always been treated as unaliged accesses and handled
> > > as such. But address errors are also issued for illegal accesses like
> > > user to kernel space or accesses outside of implemented spaces. This
> > > change implements Linux exception handling for accesses to the illegal
> > > space above the CPU implemented maximum virtual user address and the
> > > MIPS 64bit architecture maximum. With this we can now use a fixed value
> > > for the maximum task size on every MIPS CPU and get a more optimized
> > > access_ok().
> > >
> > > Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> >
> > Thank you for addressing this. Should I add this patch to my series
> > ahead of "mips: use simpler access_ok()"? That way I can keep it all
> > in my asm-generic tree as a series for 5.18.
>
> yes please add it to your series.

Done now.

> >
> > It might be clearer to use TASK_SIZE_MAX here instead of XKSSEG,
> > to match the check in access_ok(). If you like, I can change that while
> > applying.
>
> I had TASK_SIZE_MAX in an intermediate version, but decided to go with XKSSEG,
> because it's what this check is about. It's about checking what the MIPS
> architecture defined.

Right, makes sense.

Thanks,

        Arnd