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Subject: Re: [RFC 00/19] KVM: s390/crypto/vfio: guest dedicated crypto
 adapters
To:     Cornelia Huck <cohuck@redhat.com>
Cc:     Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
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        qemu-s390x@nongnu.org, jjherne@linux.vnet.ibm.com,
        thuth@redhat.com, pasic@linux.vnet.ibm.com
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From:   Pierre Morel <pmorel@linux.vnet.ibm.com>
Date:   Thu, 16 Nov 2017 21:25:16 +0100
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On 16/11/2017 18:03, Cornelia Huck wrote:
> On Thu, 16 Nov 2017 17:06:58 +0100
> Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:
> 
>> On 16/11/2017 16:23, Tony Krowiak wrote:
>>> On 11/14/2017 08:57 AM, Cornelia Huck wrote:
>>>> On Tue, 31 Oct 2017 15:39:09 -0400
>>>> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:
>>>>   
>>>>> On 10/13/2017 01:38 PM, Tony Krowiak wrote:
>>>>> Ping
>>>>>> Tony Krowiak (19):
>>>>>>      KVM: s390: SIE considerations for AP Queue virtualization
>>>>>>      KVM: s390: refactor crypto initialization
>>>>>>      s390/zcrypt: new AP matrix bus
>>>>>>      s390/zcrypt: create an AP matrix device on the AP matrix bus
>>>>>>      s390/zcrypt: base implementation of AP matrix device driver
>>>>>>      s390/zcrypt: register matrix device with VFIO mediated device
>>>>>>        framework
>>>>>>      KVM: s390: introduce AP matrix configuration interface
>>>>>>      s390/zcrypt: support for assigning adapters to matrix mdev
>>>>>>      s390/zcrypt: validate adapter assignment
>>>>>>      s390/zcrypt: sysfs interfaces supporting AP domain assignment
>>>>>>      s390/zcrypt: validate domain assignment
>>>>>>      s390/zcrypt: sysfs support for control domain assignment
>>>>>>      s390/zcrypt: validate control domain assignment
>>>>>>      KVM: s390: Connect the AP mediated matrix device to KVM
>>>>>>      s390/zcrypt: introduce ioctl access to VFIO AP Matrix driver
>>>>>>      KVM: s390: interface to configure KVM guest's AP matrix
>>>>>>      KVM: s390: validate input to AP matrix config interface
>>>>>>      KVM: s390: New ioctl to configure KVM guest's AP matrix
>>>>>>      s390/facilities: enable AP facilities needed by guest
>>>> I think the approach is fine, and the code also looks fine for the most
>>>> part. Some comments:
>>>>
>>>> - various patches can be squashed together to give a better
>>>>     understanding at a glance
>>> Which patches would you squash?
>>>> - this needs documentation (as I already said)
>>> My plan is to take the cover letter patch and incorporate that into
>>> documentation,
>>> then replace the cover letter patch with a more concise summary.
>>>> - some of the driver/device modelling feels a bit awkward (commented in
>>>>     patches) -- I'm not sure that my proposal is better, but I think we
>>>>     should make sure the interdependencies are modeled correctly
>>> I am responding to each patch review individually.
>>
>> I think that instead of responding to each patch individually we should
>> have a discussion on the design because I think a lot could change and
>> discussing about each patch as they may be completely redesigned for the
>> next version may not be very useful.
>>
>> So I totally agree with Conny on that we should stabilize the
>> bus/device/driver modeling.
>>
>> I think it would be here a good place to start the discussion on things
>> like we started to discuss, Harald and I, off-line:
>> - why a matrix bus, in which case we can avoid it
> 
> I thought it had been agreed that we should be able to ditch it?

I have not see any comment on the matrix bus.

> 
>> - which kind of devices we need
> 
> What is still unclear? Which card generations to support?

No, I mean the relation bus/device/driver/mdev...

> 
>> - how to handle the repartition of queues on boot, reset and hotplug
> 
> That's something I'd like to see a writeup for.

yes, and it may have an influence on the bus/device/driver/mdev design

> 
>> - interaction with the host drivers
> 
> The driver model should already handle that, no?

yes it should, but it is not clear for me.

> 
>> - validation of the matrix for guests and host views
> 
> I saw validation code in the patches, although I have not reviewed it.
> 
>>
>> or even features we need to add like
>> - interruptions
> 
> My understanding is that interrupts are optional so they can be left
> out in the first shot. With the gisa (that has not yet been posted), it
> should not be too difficult, no?

you are right I forgot that it is optional

> 
>> - PAPQ/TAPQ-t and APQI interception
> 
> I can't say anything about that, as this is not documented :(

Right we can live without these too.

> 
>> - virtualization of the AP
> 
> Is this really needed? It would complicate everything a lot.

Concern has no sens without interception.
> 
>> - CPU model and KVM capabilities
> 
> That already has been discussed with the individual patches.

Well, if there are no interceptions the individual patches discussions 
are enough.

> 
>>
>> In my understanding these points must be cleared before we really start
>> to discuss the details of the implementation.
> 
> The general design already looks fine to me. Do you really expect that
> a major redesign is needed?
> 

I am worry about the following:
- Will the matrix bus be accepted
- What happens on host reset and hot plug/unplug in host
- What happens with the queues on guest start/halt/restart

Regards,

Pierre

-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany


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