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

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Message-Id: <ecb24dd6-3fb9-6a5f-165c-dfb7344c5743@linux.ibm.com>
Date:   Tue, 3 Jul 2018 10:44:10 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Halil Pasic <pasic@...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 07/02/2018 12:28 PM, Cornelia Huck wrote:
> On Mon, 2 Jul 2018 18:20:55 +0200
> Halil Pasic <pasic@...ux.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@...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.
>>>    
>> 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.

Consider it done.

>