linux-kernel - Re: [PATCH 15/15] x86: use non-set

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Message-ID: <CAHk-=wi6E5z_aKr9NX+QcEJqJvSyrDbO3ypPugxstcPV5EPSMQ@mail.gmail.com>
Date:   Wed, 6 May 2020 10:51:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     "the arch/x86 maintainers" <x86@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-parisc@...r.kernel.org,
        linux-um <linux-um@...ts.infradead.org>,
        Netdev <netdev@...r.kernel.org>, bpf@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 15/15] x86: use non-set_fs based maccess routines

On Tue, May 5, 2020 at 11:23 PM Christoph Hellwig <hch@....de> wrote:
>
> +#define arch_kernel_read(dst, src, type, err_label)                    \
> +       __get_user_size(*((type *)dst), (__force type __user *)src,     \
> +                       sizeof(type), __kr_err);                        \
..
> +#define arch_kernel_write(dst, src, type, err_label)                   \
> +       __put_user_size(*((type *)(src)), (__force type __user *)(dst), \
> +                       sizeof(type), err_label)

My private tree no longer has those __get/put_user_size() things,
because "unsafe_get/put_user()" is the only thing that remains with my
conversion to asm goto.

And we're actively trying to get rid of the whole __get_user() mess.
Admittedly "__get_user_size()" is just the internal helper that
doesn't have the problem, but it really is an internal helper for a
legacy operation, and the new op that uses it is that
"unsafe_get_user()".

Also, because you use __get_user_size(), you then have to duplicate
the error handling logic that we already have in unsafe_get_user().

IOW - is there some reason why you didn't just make these use
"unsafe_get/put_user()" directly, and avoid both of those issues?

              Linus