Re: [Qemu-devel] [Qemu-ppc] [GIT PULL for qemu-pseries REPOST] pseries: Update SLOF firmware image

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Aug 23, 2019 at 02:09:44PM +1000, Alexey Kardashevskiy wrote:
> 
> 
> On 14/08/2019 14:33, Aravinda Prasad wrote:
> > 
> > 
> > On Tuesday 13 August 2019 07:47 PM, David Gibson wrote:
> > > On Tue, Aug 13, 2019 at 01:00:24PM +0530, Aravinda Prasad wrote:
> > > > 
> > > > 
> > > > On Monday 12 August 2019 03:38 PM, David Gibson wrote:
> > > > > On Mon, Aug 05, 2019 at 02:14:39PM +0530, Aravinda Prasad wrote:
> > > > > > Alexey/David,
> > > > > > 
> > > > > > With the SLOF changes, QEMU cannot resize the RTAS blob. Resizing is
> > > > > > required for FWNMI support which extends the RTAS blob to include an
> > > > > > error log upon a machine check.
> > > > > > 
> > > > > > The check to valid RTAS buffer fails in the guest because the rtas-size
> > > > > > updated in QEMU is not reflecting in the guest.
> > > > > > 
> > > > > > Any workaround for this?
> > > > > 
> > > > > Well, we should still be able to do it, it just means fwnmi would need
> > > > > a SLOF change.  It's an inconvenience, but not really a big deal.
> > > > 
> > > > Yes. Alexey and I were discussing about the following changes to SLOf:
> > > > 
> > > > diff --git a/lib/libhvcall/hvcall.S b/lib/libhvcall/hvcall.S
> > > > index b19f6dbeff2c..880d29a29122 100644
> > > > --- a/lib/libhvcall/hvcall.S
> > > > +++ b/lib/libhvcall/hvcall.S
> > > > @@ -134,6 +134,7 @@ ENTRY(hv_rtas)
> > > >          ori     r3,r3,KVMPPC_H_RTAS@l
> > > >          HVCALL
> > > >          blr
> > > > +    .space 2048
> > > >          .globl hv_rtas_size
> > > >   hv_rtas_size:
> > > >          .long . - hv_rtas;
> > > > 
> > > > 
> > > > But this will statically reserve space for RTAS even when
> > > > SPAPR_CAP_FWNMI_MCE is OFF.
> > > 
> > > Sure.  We could flag that in the DT somehow, and have SLOF reserve the
> > > space conditionally.
> > > 
> > > Or we could just ignore it. 2 kiB is miniscule compared to our minimum
> > > guest size, and our current RTAS is microscopic compared to PowerVM.
> > 
> > I also think so, 2kiB is miniscule so we can allocate it statically.
> > 
> > Alexey,
> > 
> > Can you please include the above one line fix to SLOF?
> 
> 
> I am thinking of:
> ===
> @@ -132,20 +132,22 @@ ENTRY(hv_rtas)
>  	mr	r4,r3
>  	lis	r3,KVMPPC_H_RTAS@h
>  	ori	r3,r3,KVMPPC_H_RTAS@l
>  	HVCALL
>  	blr
> +	.space 2048 - (. - hv_rtas)
>  	.globl hv_rtas_size
>  hv_rtas_size:
>  	.long . - hv_rtas;
> 
>  ENTRY(hv_rtas_broken_sc1)
>  	mr	r4,r3
>  	lis	r3,KVMPPC_H_RTAS@h
>  	ori	r3,r3,KVMPPC_H_RTAS@l
>  	.long	0x7c000268
>  	blr
> +	.space 2048 - (. - hv_rtas_broken_sc1)
>  	.globl hv_rtas_broken_sc1_size
>  hv_rtas_broken_sc1_size:
>  	.long . - hv_rtas_broken_sc1;
> ===
> 
> to align the rtas blob to 2k precisely. But QEMU hardcoded
> RTAS_ERROR_LOG_OFFSET bothers me a bit, I should probably put some sort of a
> magic marker at which RTAS log can start.
> 
> David, any thoughts? The marker could be as simple as a zero, for example.

Eh, TBH I don't think an agreed upon magic marker has all that much
advantage on an agreed upon offset.  Let's keep it simple and retain
the fixed offset for now.  If that's ever a problem we'll need a
synchronized qemu & SLOF update, but that's ok - that's an
inconvenience, not a disaster.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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