linux-kernel - Re: [PATCH v9 22/22] s390: doc: detailed specifications for AP virtualization

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Date:   Wed, 22 Aug 2018 09:38:30 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        kwankhede@...dia.com, bjsdjshi@...ux.vnet.ibm.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pmorel@...ux.vnet.ibm.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com,
        frankja@...ux.ibm.com
Subject: Re: [PATCH v9 22/22] s390: doc: detailed specifications for AP
 virtualization

On Tue, 21 Aug 2018 20:54:49 +0200
Halil Pasic <pasic@...ux.ibm.com> wrote:

> On 08/20/2018 10:16 PM, Tony Krowiak wrote:
> >> Does the SIE complain if you specify a control
> >> domain that the host does not have access to (I'd guess so)?  
> > 
> > The SIE does not complain if you specify a domain to which the host - or a
> > lower level guest - does not have access. The firmware performs a logical
> > AND of the guest's and hosts's - or lower level guest's - APMs, AQMs and ADMs  
> 
> Rather a bit-wise AND, I guess (of the same type masks corresponding to Guest 1 and
> Guest 2). The result of a logical AND is a logical value (true or false) as
> far as I remember.
> 
> > to create effective masks EAPM, EAQM and EADM. Only devices corresponding to
> > the bits set in the EAPM, EAQM and EADM will be accessible by the guest.  
> 
> I'm not sure what is the intended meaning of 'the SIE complains'. If it means
> getting out of (SIE when interpreting lets say an NQAP under the discussed
> circumstances) with some sort of error code, I think Tony's answer, ' SIE does not complain'
> makes a lot of sense. It's the guest that's is trying to stretch further than
> the blanket reaches, and it's the guest that needs to be educated on this fact.

Yep, that's what I meant. If the hypervisor can call the SIE with that
config, but the guest gets an error if it tries to use something that
it cannot use, that's fine.