linux-kernel - Re: [PATCH V3 07/17] riscv: compat: Re-implement TASK_SIZE for COMPAT

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Date:   Thu, 20 Jan 2022 21:27:08 +0800
From:   Guo Ren <guoren@...nel.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Palmer Dabbelt <palmer@...belt.com>,
        Anup Patel <anup@...infault.org>,
        gregkh <gregkh@...uxfoundation.org>,
        liush <liush@...winnertech.com>, Wei Fu <wefu@...hat.com>,
        Drew Fustini <drew@...gleboard.org>,
        Wang Junqiang <wangjunqiang@...as.ac.cn>,
        Christoph Hellwig <hch@....de>,
        Christoph Hellwig <hch@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        "inux-parisc@...r.kernel.org" <inux-parisc@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH V3 07/17] riscv: compat: Re-implement TASK_SIZE for COMPAT_32BIT

On Thu, Jan 20, 2022 at 8:53 PM David Laight <David.Laight@...lab.com> wrote:
>
> > > Limit 32-bit compatible process in 0-2GB virtual address range
> > > (which is enough for real scenarios), because it could avoid
> > > address sign extend problem when 32-bit enter 64-bit and ease
> > > software design.
>
> Eh?
> I thought nearly all the other 32bit unix ports (of any flavour)
> put the user-kernel boundary at 3GB.
No, riscv32 is about 2.4G, csky is 2G/2.5G.

> (Apart from some very old sparc ones that use 3.5GB.)
>
> 2GB is used by Windows.
>
> I think the x86-64 32bit compat code even puts the boundary at 4GB.
Yes, we could give rv32 compat for 4GB with some effort. But it's unnecessary.

There are no history issues for rv32, we use compat mode to reduce
memory footprint. eg: only 64MB memory available.

At end compat for 4GB is another topic, let's give the initial compat
for 2GB support to riscv.

>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/