* Andy Lutomirski <l...@amacapital.net> wrote:
> >> Strengthen the SMAP protection by addding the missing ASM_CLAC right at
> >> the
> >> beginning.
> >
> > Hmmm... this potentially adds a *lot* of unnecessary cycles to this path.
> > Could we reinstate the early uaccess?
>
> I think that's more trouble than it's worth, and it'll undo a bunch of the
> context tracking cleanups that deferring it made possible, especially since
> this
> only matters in a configuration (32-bit SMAP) that no one uses. [1]
But but ... 'context tracking' is not really something that a regular distro
kernel cares about much - it's a nohz-full special AFAICS.
So if the only reason to keep this overhead is to simplify context tracking
then
I'm pretty sure we want to burden context-tracking with that, not the common
fast
path.
Anyway, maybe we are 'lucky':
> *However*, I just realized that I have no idea why the 32-bit sysenter
> path is safe against NT being set. I fixed it on compat, and now I'm
> confused as to the status on 32-bit. If we need to fix up NT, I think
> we can fold AC into that.
>
> Also, I'll try to benchmark this soon.
Sounds good, thanks!
Ingo
