Re: [PATCH] x86: only use ERMS for user copies for larger sizes

[Linus Torvalds]

On Thu, Nov 22, 2018 at 2:32 AM Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Random patch (with my "asm goto" hack included) attached, in case
> > people want to play with it.
>
> Doesn't even look all that hacky to me. Any hack in it that I didn't
> notice? :-)

The code to use asm goto sadly doesn't have any fallback at all for
the "no asm goto available".

I guess we're getting close to "we require asm goto support", but I
don't think we're there yet.

Also, while "unsafe_put_user()" has been converted to use asm goto
(and yes, it really does generate much nicer code), the same is not
true of "unsafe_get_user()". Because sadly, gcc does not support asm
goto with output values.

So, realistically, my patch is not _technically_ hacky, but it's
simply not viable as things stand, and it's more of a tech
demonstration than anything else.

               Linus