RE: xsaves support broken?

From: Yu, Fenghua
Date: Mon Mar 02 2015 - 19:34:09 EST


> From: Hansen, Dave
> On 03/02/2015 04:09 PM, Yu, Fenghua wrote:
> > Xsaves has been tested by QA since 3.17 with or without MPX. I'm not
> > aware of reported issues.
> >
> > But MPX is the only code to call the get_xsave_addr kernel API.
> > Though it has been tested before on upstream MPX code.
>
> Has it? I'm fairly sure I've never explicitly tested it. I'm also doubting now
> that I've *ever* seen it work without booting with 'noxsaves'.

QA did test conflict between MPX and xsaves long time before MPX went upstream. But seems the conflict happened again at some point...

>
> > What changes in your new MPX code?
>
> I just discovered it when adding a new feature. I actually backed out all of my
> changes before reporting this issue. I'm running a completely untouched 4.0-
> rc1 kernel with the config I attached a moment ago.

MPX and xsaves are supposed to work well on 4.0-rc1. If not, definitely the code is broken again somehow.

> If I boot with 'noxsaves', MPX works fine. If I boot without it, the kernel
> never sees the values that userspace sets in the "bndcsr" register.

We are supposed to handle this issue long time ago.

I can try to reproduce the issue with the config.

Thanks.

-Fenghua