Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok

[Linus Torvalds]

On Sat, Jan 6, 2018 at 3:31 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> I assume if we put this in uaccess_begin() we also need audit for
> paths that use access_ok but don't do on to call uaccess_begin()? A
> quick glance shows a few places where we are open coding the stac().
> Perhaps land the lfence in stac() directly?

Yeah, we should put it in uaccess_begin(), and in the actual user
accessor helpers that do stac. Some of them probably should be changed
to use uaccess_begin() instead while at it.

One question for the CPU people: do we actually care and need to do
this for things that might *write* to something? The speculative write
obviously is killed, but does it perhaps bring in a cacheline even
when killed?

Because maybe we don't need the lfence in put_user(), only in get_user()?

               Linus