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Date: Fri, 15 Dec 2017 12:58:48 +1000
From: Nicholas Piggin <npiggin@gmail.com>
To: Balbir Singh <bsingharora@gmail.com>
Cc: "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)"
 <linuxppc-dev@lists.ozlabs.org>, Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v3 2/3] powerpc/powernv: Identify scom driven system reset
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On Fri, 15 Dec 2017 13:54:18 +1100
Balbir Singh <bsingharora@gmail.com> wrote:

> On Fri, Dec 15, 2017 at 1:44 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
> > On Fri, 15 Dec 2017 12:27:39 +1100
> > Balbir Singh <bsingharora@gmail.com> wrote:
> >  
> >> In irq_set_pending_from_srr1() we were missing 0x2 as system
> >> reset identified from SRR1 caused by back to back system
> >> resets or when interrupts are caused by SCOM when the thread
> >> is not in power saving mode.
> >>
> >> This helps us get to NMI handling in both the case where NMI
> >> is caused when in power-saving and not in power-saving mode.
> >> The actual exploitation is expected when we are doing a kdump
> >> and an offline CPU might not be in power-saving mode due to
> >> an already spurious IPI or any other reason.
> >>
> >> Signed-off-by: Balbir Singh <bsingharora@gmail.com>  
> >
> > When not in power saving mode, we don't look at SRR1 at all, so
> > we don't need this. You should never be getting it returned as the
> > result of your idle instruction (except on DD1 which has a bug,
> > but firmware doesn't implement the NMI IPI).
> >  
> 
> I added this for the next patch. We call irq_set_pending_from_srr1
> while coming out of CPU idle, but if for any reason the IPI was spurious
> and then we see an NMI during kdump, I did want to detect that
> and callback into the NMI handler.

You'll never see it. The SRR1 value you get is the idle wakeup code.
So any scom-when-not-idle bit should never be set.

Thanks,
Nick