Subject: Re: [PATCH] powerpc: Invalidate ERAT on powersave wakeup for POWER9

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 23 Jun 2017 05:45:36 -0500

On Fri, 2017-06-23 at 19:33 +1000, Michael Ellerman wrote:
> Michael Neuling <[email-masked]> writes:
> 
> > On POWER9 the ERAT may be incorrect on wakeup from some stop states
> > that lose state. This causes random segvs and illegal instructions
> > when these stop states are enabled.
> 
> Incorrect how?

As in stale. Not sure about the details.

> Because with the ERAT flush where you've put it, there's still a good
> amount of code executed prior to the flush isn't there?

In real mode, should be ok.

> ie. we come in at 0x100, do some of the prolog, do IDLE_TEST which takes
> us to pnv_powersave_wakeup, which then restores state from the paca
> (memory), that returns and then we check KVM ... and then finally we end
> up at pnv_wakeup_loss.
> 
> Or is there some other path? Or is the ERAT incorrect in some specific
> way which means we only need to flush there?

I think real mode translations are ok but I'll ask around.

Cheers,
Ben.

> cheers
> 
> > diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
> > index 1ea14b96f1..ace2ad50c8 100644
> > --- a/arch/powerpc/kernel/idle_book3s.S
> > +++ b/arch/powerpc/kernel/idle_book3s.S
> > @@ -793,6 +793,9 @@ fastsleep_workaround_at_exit:
> >   */
> >  .global pnv_wakeup_loss
> >  pnv_wakeup_loss:
> > +BEGIN_FTR_SECTION
> > +	PPC_INVALIDATE_ERAT
> > +END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> >  	ld	r1,PACAR1(r13)
> >  BEGIN_FTR_SECTION
> >  	CHECK_HMI_INTERRUPT
> > -- 
> > 2.11.0