linux-kernel - Re: [PATCH v6 05/21] KVM: s390: CPU model support for AP virtualization

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Date:   Mon, 2 Jul 2018 18:11:08 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...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, 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
Subject: Re: [PATCH v6 05/21] KVM: s390: CPU model support for AP
 virtualization

On Mon, 2 Jul 2018 11:54:28 -0400
Tony Krowiak <akrowiak@...ux.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@...ux.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@...ibm.com>
> >>>> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
> >>>> Signed-off-by: Tony Krowiak <akrowiak@...ux.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.