Re: [patch 0/8] x86/fpu: Mop up XSAVES and related damage

[Yu, Yu-cheng]

On 6/4/2021 7:05 AM, Thomas Gleixner wrote:
> On Wed, Jun 02 2021 at 14:28, Yu-cheng Yu wrote:
> > On 6/2/2021 2:55 AM, Thomas Gleixner wrote:
> >
> > With the series applied, glibc pkey test fails sometimes.  I will try to
> > find out the cause.
>
> That fails not sometimes. It fails always due to patch 7/8. The reason
> is that before that patch fpu__clear_all() reinitialized the hardware
> which includes writing the initial PKRU value.
>
> But fpu__initialize() does not store the initial PKRU value in the
> task's xstate which breaks PKRU. As that patch is not urgent we can
> postpone it for not.
>
> But looking at the above, it's not clear to me why that PKRU stuff works
> at all (upstream), but I'll figure it out eventually. I'm quite sure
> that it does work by pure chance not by design.

Thanks for the update.  I will continue looking at it.

Yu-cheng