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    SubjectRe: [PATCH v6 05/21] KVM: s390: CPU model support for AP virtualization
    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.

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