Re: [Qemu-devel] [RFC 00/19] KVM: s390/crypto/vfio: guest dedicated crypto adapters

[Tony Krowiak <akrowiak@linux.vnet.ibm.com>]

On 10/30/2017 04:57 AM, Christian Borntraeger wrote:
> adding qemu devel and add Daniel and Erik from libvirt to keep them in the loop.
>
> On 10/29/2017 12:11 PM, Cornelia Huck wrote:
>> On Fri, 13 Oct 2017 13:38:45 -0400
>> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:
>>
>>> 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'll try to summarize all of this in my own words, both to make sure I
>> understand the design correctly and to give others a different view on
>> this.
>>
>> [I'm completely disregarding control domains here.]
>>
>> On s390, we have cryptographic coprocessor cards, which are modeled on
>> Linux as devices on the AP bus. There's also a concept called domains,
>> which means an individual queue of a crypto device is basically a
>> (card,domain) tuple. We model this something like the following
>> (assuming we have access to cards 3 and 4 and domains 1 and 2):
>>
>> AP -> card3 -> queue (3,1)
>>              -> queue (3,2)
>>     -> card4 -> queue (4,1)
>>              -> queue (4,2)
>>
>> (The AP bus is a bit different for backwards compat.)
>>
>> If we want to virtualize this, we can use a feature provided by the
>> hardware. We basically attach a satellite control block to our main
>> hardware virtualization control block and the hardware takes care of
>> (mostly) everything.
>>
>> For this control block, we don't specify explicit tuples, but a list of
>> cards and a list of domains. The guest will get access to the cross
>> product.
>>
>> Because of this, we need to take care that the lists provided to
>> different guests don't overlap; i.e., we need to enforce sane
>> configurations. Otherwise, one guest may get access to things like
>> secret keys for another guest.
>>
>> The idea of this patch set is to introduce a new device, the matrix
>> device. This matrix device hangs off a different root and acts as the
>> node where mdev devices hang off.
>>
>> If you now want to give the tuples (4,1) and (4,2), you need to do the
>> following:
>>
>> - Unbind the (4,1) and (4,2) tuples from their ap bus driver.
>> - Bind the (4,1) and (4,2) tuples to the ap matrix driver.
>> - Create the mediated device.
>> - Assign card 4 and domains 1 and 2.
>>
>> QEMU will now simply consume the mediated device and things should work.
>>
> This is probably the shortest possible summary I can imagine.
> Tony can you double check if it matches your understanding as well?
>
Yes, this is a concise summary of the patch set.