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Date: Wed, 5 Dec 2018 12:54:29 +0100
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] [qemu-s390x] [PATCH v1] s390: guest support for
 diagnose 318 and limit max VCPUs to 247
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To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: David Hildenbrand <david@redhat.com>, Collin Walling <walling@linux.ibm.com>, cornelia.huck@de.ibm.com, cotte@de.ibm.com, mimu@linux.ibm.com, qemu-s390x@nongnu.org, qemu-devel@nongnu.org, thuth@redhat.com

On Wed, 5 Dec 2018 09:27:44 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 05.12.2018 09:26, David Hildenbrand wrote:
> > On 04.12.18 23:18, Collin Walling wrote:  
> >> Add migration and reset support for diagnose 318. This is a new z14 GA2 
> >> hardware feature, but we can provide guest support starting with the 
> >> zEC12-full CPU model.
> >>
> >> Because new hardware introduces a new facility-availability byte in 
> >> the Read SCP Info block, we lose one byte in the CPU entries list 
> >> and must limit the maximum VCPUs to 247 (down from 248).  
> > 
> > This could break setups that upgrade/migrate. At least forward migration
> > can be broken. Do we care about that?  
> 
> Can we maybe bind this feature and the cpu limit to the 4.0 machine?

I think that would make sense.

> > 
> > Can you split off
> > 
> > 1. linux-header changes
> > 2. CPU model changes? (introduction and definition of new feature, but
> > not when it is used?)
> >   
> >>
> >> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> >> ---