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

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Date:   Tue, 21 Aug 2018 20:54:49 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     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 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.

AFAIR SIE does the right thing (whatever the right thing is) and we don't have to
worry about it.

As a matter of fact I can't recall exactly what is supposed to happen
when a guest tries to modify a domain such that the guest does not
have privileges to modify (in terms of EADM, either because the
guest or because the host does not have the corresponding bit set). I'm sure
I did not try it out. Tony did you test this scenario? (BTW my best guess
at the moment is, that the situation is handled via the command-reply.)

Regards,
Halil