linux-kernel - Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback

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Date:   Mon, 11 Jun 2018 08:56:02 -0400
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     pmorel@...ux.ibm.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...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,
        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 v5 11/13] KVM: s390: implement mediated device open
 callback

On 06/11/2018 05:23 AM, Pierre Morel wrote:
> On 08/06/2018 23:59, Tony Krowiak wrote:
>> On 06/07/2018 01:15 PM, Pierre Morel wrote:
>>>
>
> ...snip...
>
>>>>>
>>>>>>
>>>>>> Why maintain a list of kvm_ap_matrix structures if we don't have 
>>>>>> to; it is stored
>>>>>> with the mediated matrix device which is passed in to all of the 
>>>>>> vfio_ap driver
>>>>>> callbacks.
>>>>>
>>>>> Because using the vm_list which is a static in kvm makes you stick 
>>>>> inside the kvm code.
>>
>> I understand your point here, but even if we did maintain a list of 
>> kvm_ap_matrix structures,
>> we still need the kvm code to configure the guest's CRYCB and 
>> eventually ECA.28. There is
>> also code in kvm-ap.c that is called from KVM.
>
> The only code from kvm-ap which is called from KVM is temporary code
> waiting for Harald to offer the clean interface to AP instructions.
>
>> The idea behind kvm-ap.c is that all code
>> related to configuration of AP structures in KVM is in this one spot.
>
> This I understand, but the code can be in one spot inside VFIO_AP instead
> of inside KVM.
> Putting the code inside KVM induce dependencies between KVM and AP
> while the kvm/vfio interface allows to avoid this dependency.
>
>
> The purpose of VFIO_AP is to handle the CRYCB, all get/clear/set crycb 
> masks
> functions should be in VFIO AP.
>
> If we use wrappers in KVM, since the CRYCB is an a SIE extension,
> it is legitimate, the KVM interface to the CRYCB should only
> handle bitmaps and be unaware of the vfio_ap internal structures.
>
>
> Another concern, the kvm_ap_validate_queue_sharing() should not be
> inside KVM because it is a decision of current VFIO_AP driver
> to not share the queues between guest of level 2.
>
> The Z architecture does not allow to share AP queues between
> guests of level 1 but we could re-engineer the AP bus and the '
> VFIO AP to offer queue sharing for guest level 2.
>
> This would be a new VFIO_AP driver (and an AP bus extension).
> We should not have to change KVM for this.

Based on your, Halil's and Janosch's comments, I will make the changes.

>
>
>
> Regards,
>
> Pierre
>
>
>>
>>>
>>>
>>>
>>
>