Re: [PATCH 15/15] x86: use non-set_fs based maccess routines

[Linus Torvalds]

On Tue, May 5, 2020 at 11:23 PM Christoph Hellwig <hch@xxxxxx> 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