linux-kernel - Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest

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Message-Id: <718086fa-9f9e-e474-371e-cf0a89f5460c@de.ibm.com>
Date:   Fri, 3 Nov 2017 09:49:46 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Harald Freudenberger <FREUDE@...ibm.com>,
        Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, heicars2@...ux.vnet.ibm.com,
        cohuck@...hat.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,
        qemu-s390x@...gnu.org, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com,
        borntrAE@...ux.vnet.ibm.com
Subject: Re: [RFC 19/19] s390/facilities: enable AP facilities needed by guest



On 11/03/2017 09:14 AM, Harald Freudenberger wrote:
> I talked with the firmware guys about this.
> The answer is that the AP 3 instructions (NQAP, DQAP, PQAP) are always available.

That is true for basic mode and LPAR, but certainly not for z/VM or KVM guests.


> Tony is right with the facility bits.
> facility bit 15 tells if the T bit is supported with the PQAP(TAPQ) subcommand,
> facility bit 12 tells if the PQAP(QCI) subcommand is available.
> 
> As far as I could discover the AP instructions where optional on some older machines.
> This may be the reason why zVM throws an exception if there is no AP device assigned.
> However, for all machines still in service the AP instructions are available at al time.

We have to distinguish LPARs and 2nd level guests under KVM/z/VM. For those 2nd level
guests there are configurations out there TODAY that do not support PQAP and friends.