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

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Message-ID: <CAAhV-H7B2tqw-PWD2775Nx1JiPVwh8nGYsVDTiA0QjBhTYbrMw@mail.gmail.com>
Date:   Sat, 7 Oct 2023 12:55:14 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Deepak R Varma <drv@...lo.com>
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

Hi, Deepak,

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.

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

Huacai

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