regression suspend/resume on Lenovo T420

[Konstantin Belousov]

On Mon, May 15, 2017 at 02:37:16PM -0230, Jonathan Anderson wrote:
> On 15 May 2017, at 7:26, Konstantin Belousov wrote:
> >
> > Try this.  If it works, I will write a proper patch.
> >
> > diff --git a/sys/amd64/amd64/cpu_switch.S 
> > b/sys/amd64/amd64/cpu_switch.S
> > index 33437ad16e6..9c0cd05ebea 100644
> > --- a/sys/amd64/amd64/cpu_switch.S
> > +++ b/sys/amd64/amd64/cpu_switch.S
> > @@ -369,6 +369,11 @@ END(savectx)
> >   * Resuming processor state from pcb.
> >   */
> >  ENTRY(resumectx)
> > +	movl	$MSR_EFER,%ecx
> > +	rdmsr
> > +	orl	$EFER_NXE,%eax
> > +	wrmsr
> > +
> >  	/* Switch to KPML4phys. */
> >  	movq	KPML4phys,%rax
> >  	movq	%rax,%cr3
> 
> Running drm-next (which has -CURRENT last merged somewhere around 
> r317651), this patch fixes one of the two problems I've been 
> experiencing with suspend/resume. Definite progress. :)

Could you, please, clarify.  Does the resume work after this  ?  If not,
how did you diagnosed that 'one of two problems' is solved with the change ?