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Date:   Mon, 2 Jul 2018 18:28:40 +0200
From:   Cornelia Huck <cohuck@redhat.com>
To:     Halil Pasic <pasic@linux.ibm.com>
Cc:     Tony Krowiak <akrowiak@linux.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, freude@de.ibm.com, schwidefsky@de.ibm.com,
        heiko.carstens@de.ibm.com, kwankhede@nvidia.com,
        bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
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        pasic@linux.vnet.ibm.com, berrange@redhat.com,
        fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com
Subject: Re: [PATCH v6 05/21] KVM: s390: CPU model support for AP
 virtualization
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On Mon, 2 Jul 2018 18:20:55 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On 07/02/2018 06:11 PM, Cornelia Huck wrote:
> > On Mon, 2 Jul 2018 11:54:28 -0400
> > Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >   
> >> On 07/02/2018 11:41 AM, Cornelia Huck wrote:  
> >>> On Mon, 2 Jul 2018 11:37:11 -0400
> >>> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >>>     
> >>>> On 07/02/2018 10:38 AM, Christian Borntraeger wrote:  
> >>>>> On 06/29/2018 11:11 PM, Tony Krowiak wrote:  
> >>>>>> Introduces a new CPU model feature and two CPU model
> >>>>>> facilities to support AP virtualization for KVM guests.
> >>>>>>
> >>>>>> CPU model feature:
> >>>>>>
> >>>>>> The KVM_S390_VM_CPU_FEAT_AP feature indicates that
> >>>>>> AP instructions are available on the guest. This
> >>>>>> feature will be enabled by the kernel only if the AP
> >>>>>> instructions are installed on the linux host. This feature
> >>>>>> must be specifically turned on for the KVM guest from
> >>>>>> userspace to use the VFIO AP device driver for guest
> >>>>>> access to AP devices.
> >>>>>>
> >>>>>> CPU model facilities:
> >>>>>>
> >>>>>> 1. AP Query Configuration Information (QCI) facility is installed.
> >>>>>>
> >>>>>>       This is indicated by setting facilities bit 12 for
> >>>>>>       the guest. The kernel will not enable this facility
> >>>>>>       for the guest if it is not set on the host. This facility
> >>>>>>       must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
> >>>>>>       feature is not installed.
> >>>>>>
> >>>>>>       If this facility is not set for the KVM guest, then only
> >>>>>>       APQNs with an APQI less than 16 will be available to the
> >>>>>>       guest regardless of the guest's matrix configuration. This
> >>>>>>       is a limitation of the AP bus running on the guest.
> >>>>>>
> >>>>>> 2. AP Facilities Test facility (APFT) is installed.
> >>>>>>
> >>>>>>       This is indicated by setting facilities bit 15 for
> >>>>>>       the guest. The kernel will not enable this facility for
> >>>>>>       the guest if it is not set on the host. This facility
> >>>>>>       must not be set by userspace if the KVM_S390_VM_CPU_FEAT_AP
> >>>>>>       feature is not installed.
> >>>>>>
> >>>>>>       If this facility is not set for the KVM guest, then no
> >>>>>>       AP devices will be available to the guest regardless of
> >>>>>>       the guest's matrix configuration. This is a limitation
> >>>>>>       of the AP bus running under the guest.
> >>>>>>
> >>>>>> Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
> >>>>>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
> >>>>>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>  
> >>>>> I think it probably should be at the end of the series, other than that its good.  
> >>>> If I move this to the end of the series, the very next patch checks the
> >>>>
> >>>> KVM_S390_VM_CPU_FEAT_AP feature?  
> >>> Introduce it here, offer it only with the last patch?  
> >>
> >> I apologize, but I don't know what you mean by this. Are you suggesting
> >> this patch
> >> should only include the #define for KVM_S390_VM_CPU_FEAT_AP?  
> > 
> > Yes, just introduce the definition here (so code later in the series
> > can refer to it) and flip the switch (offer the bit) as the final
> > patch.
> >   
> 
> The other features introduced and exposed here are no different. For
> KVM_S390_VM_CPU_FEAT_AP defer exposing means defer allow_cpu_feat();
> for the STFLE features, defer adding to FACILITIES_KVM_CPUMODEL.
> 
> Anyway, I think the definition should be squashed into #6. Expose the
> features after patch #6 is in place or expose them at the end of the
> series is IMHO a matter of taste -- and I lean towards expose at the
> end of the series.

Squashing with patch 6 and enabling at the end of the series sounds
good to me as well.