linux-kernel - Re: kmap() transformation: Question about copy_user

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Message-ID: <ZSFWa44FTi48hDyE@runicha.com>
Date:   Sat, 7 Oct 2023 18:30:27 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Subject: Re: kmap() transformation: Question about copy_user_highpage

On Sat, Oct 07, 2023 at 12:55:14PM +0800, Huacai Chen wrote:
> Hi, Deepak,

Hello Huacai,

>
> On Sat, Oct 7, 2023 at 2:46 AM Deepak R Varma <drv@...lo.com> wrote:
> >
> > Hello,
> > I am attempting to work on replacing the kmap[_atomic]() calls by
> > kmap_local_page() function call. A detail on this change can be found here [0].
> >
> > I would like to know if this function:
> >         arch/loongarch/mm/init.c::copy_user_highpage()
> > is currently in use or is it a dead code?
> >
> > If this code is not in use, can this be removed instead? However, if it is in
> > use, can you comment why kmap_atomic() was preferred over kmap()
> > function call?
> I think this function will be used for the 32bit kernel, and we will
> add loongarch32 support in the near future.

Okay. Sounds good.

>
> But on the other hand, you can replace kmap_atomic() with
> kmap_local_page(), there is no special reason to use kmap_atomic().

Looks like you sent in a patch. Thank you. I was working on trying to cross
compile my patch for the arch. I still would like to attempt that. Will request
your help if I get stuck.

regards,
deepak.


>
> Huacai
>
> >
> > [0] https://lore.kernel.org/all/20201029222652.302358281@linutronix.de/
> >
> > Thank you,
> > Deepak.
> >
> >
> >