linux-kernel - Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put

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Message-ID: <CAHk-=wgOWxqwqCFuP_Bw=Hxxf9njeHJs0OLNGNc63peNd=kRqw@mail.gmail.com>
Date:   Mon, 7 Oct 2019 21:24:17 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()

On Mon, Oct 7, 2019 at 9:09 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Try the attached patch, and then count the number of "rorx"
> instructions in the kernel. Hint: not many. On my personal config,
> this triggers 15 times in the whole kernel build (not counting
> modules).

.. and four of them are in perf_callchain_user(), and are due to those
"__copy_from_user_nmi()" with either 4-byte or 8-byte copies.

It might as well just use __get_user() instead.

The point being that the silly code in the header files is just
pointless. We shouldn't do it.

            Linus