kexec reboot fails with extra wbinvd introduced for AME SME

[Dave Young]

On 01/17/18 at 11:42am, Linus Torvalds wrote:
> On Tue, Jan 16, 2018 at 11:22 PM, Dave Young <dyoung at redhat.com> wrote:
> >
> > For the kexec reboot hang, if I remove the wbinvd in stop_this_cpu()
> > then kexec works fine. like this:
> 
> Honestly, I think we should apply that patch regardless.
> 
> Using 'wbinvd' should not be some "just because of random reasons".
> There are CPU's with errata on wbinvd, and the thing in general is
> slow and nasty.
> 
> Doing the wbinvd in a loop sounds even stranger.
> 
> If we're only doing it because of some SME issue, why isn't it
> dependent on SME? And why is it inside that loop at all?
> 
> Anyway, does it work for you if you just do the wbinvd() once, outside
> the loop? Admittedly the loop shouldn't actually loop (hlt with
> interrupts disabled), but who the hell knows.. Some of the errata
> around SME have been about machine check exceptions or something.

It does not work with just once wbinvd(), and it only works with
removing the wbinvd() for me.  Tom's new post works for me as well
since my cpu is an Intel i5-4200U.

> 
> See commit a68e5c94f7d3 ("x86, hotplug: Move WBINVD back outside the
> play_dead loop") for another example where wbinvd was inside a loop
> and apparently caused some odd issues.
> 
>               Linus

Thanks for the help! Finally I get my laptop kexec & kdump works again
after solving these issues.

Thanks
Dave