Re: [RFC PATCH v1 7/9] x86: Add unsafe_copy_from_user()

Linus Torvalds
2026-04-27T22:00:36Z

On Mon, 27 Apr 2026 at 12:19, Yury Norov <ynorov@nvidia.com> wrote:
>
> This is what Linus said when added x86 implementation for copy_from_user()
> in c512c69187197:

Note that some things have happily changed in the six+ years since...

> That's partly because we have no current users of it, but also partly
> because the copy_from_user() case is slightly different and cannot
> efficiently be implemented in terms of a unsafe_get_user() loop (because
> gcc can't do asm goto with outputs).

now everybody can do asm goto with outputs.

Yes, it's disabled on older versions, so it's not *always* available,
but all modern versions do it. And if you care about performance, you
won't be using an old compiler.

Linus