From: Pierre Morel <pmorel@linux.ibm.com>
To: Tony Krowiak <akrowiak@linux.vnet.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org
Cc: freude@de.ibm.com, schwidefsky@de.ibm.com,
heiko.carstens@de.ibm.com, borntraeger@de.ibm.com,
cohuck@redhat.com, kwankhede@nvidia.com,
bjsdjshi@linux.vnet.ibm.com, pbonzini@redhat.com,
alex.williamson@redhat.com, pmorel@linux.vnet.ibm.com,
alifm@linux.vnet.ibm.com, mjrosato@linux.vnet.ibm.com,
jjherne@linux.vnet.ibm.com, thuth@redhat.com,
pasic@linux.vnet.ibm.com, berrange@redhat.com,
fiuczy@linux.vnet.ibm.com, buendgen@de.ibm.com
Subject: Re: [PATCH v5 11/13] KVM: s390: implement mediated device open callback
Date: Thu, 7 Jun 2018 17:20:40 +0200 [thread overview]
Message-ID: <ea5c2c2f-27fe-b2bf-2aa8-fbe80e77ce81@linux.ibm.com> (raw)
In-Reply-To: <f74f2d2d-36d3-7910-5511-3691a483b89f@linux.vnet.ibm.com>
On 07/06/2018 15:54, Tony Krowiak wrote:
> On 06/06/2018 01:40 PM, Pierre Morel wrote:
>> On 06/06/2018 18:08, Pierre Morel wrote:
>>> On 06/06/2018 16:28, Tony Krowiak wrote:
>>>> On 06/05/2018 08:19 AM, Pierre Morel wrote:
>>>>> On 30/05/2018 16:33, Tony Krowiak wrote:
>>>>>> On 05/24/2018 05:08 AM, Pierre Morel wrote:
>>>>>>> On 23/05/2018 16:45, Tony Krowiak wrote:
>>>>>>>> On 05/16/2018 04:03 AM, Pierre Morel wrote:
>>>>>>>>> On 07/05/2018 17:11, Tony Krowiak wrote:
>>>>>>>>>> Implements the open callback on the mediated matrix device.
>>>>>>>>>> The function registers a group notifier to receive notification
>>>>>>>>>> of the VFIO_GROUP_NOTIFY_SET_KVM event. When notified,
>>>>>>>>>> the vfio_ap device driver will get access to the guest's
>>>>>>>>>> kvm structure. With access to this structure the driver will:
>>>>>>>>>>
>>>>>>>>>> 1. Ensure that only one mediated device is opened for the guest
>>>>>>>
>>>>>>> You should explain why.
>>>>>>>
>>>>>>>>>>
>>>>>>>>>> 2. Configure access to the AP devices for the guest.
>>>>>>>>>>
>>>>>>> ...snip...
>>>>>>>>>> +void kvm_ap_refcount_inc(struct kvm *kvm)
>>>>>>>>>> +{
>>>>>>>>>> + atomic_inc(&kvm->arch.crypto.aprefs);
>>>>>>>>>> +}
>>>>>>>>>> +EXPORT_SYMBOL(kvm_ap_refcount_inc);
>>>>>>>>>> +
>>>>>>>>>> +void kvm_ap_refcount_dec(struct kvm *kvm)
>>>>>>>>>> +{
>>>>>>>>>> + atomic_dec(&kvm->arch.crypto.aprefs);
>>>>>>>>>> +}
>>>>>>>>>> +EXPORT_SYMBOL(kvm_ap_refcount_dec);
>>>>>>>>>
>>>>>>>>> Why are these functions inside kvm-ap ?
>>>>>>>>> Will anyone use this outer of vfio-ap ?
>>>>>>>>
>>>>>>>> As I've stated before, I made the choice to contain all
>>>>>>>> interfaces that
>>>>>>>> access KVM in kvm-ap because I don't think it is appropriate
>>>>>>>> for the device
>>>>>>>> driver to have to have "knowledge" of the inner workings of
>>>>>>>> KVM. Why does
>>>>>>>> it matter whether any entity outside of the vfio_ap device
>>>>>>>> driver calls
>>>>>>>> these functions? I could ask a similar question if the
>>>>>>>> interfaces were
>>>>>>>> contained in vfio-ap; what if another device driver needs
>>>>>>>> access to these
>>>>>>>> interfaces?
>>>>>>>
>>>>>>> This is very driver specific and only used during initialization.
>>>>>>> It is not a common property of the cryptographic interface.
>>>>>>>
>>>>>>> I really think you should handle this inside the driver.
>>>>>>
>>>>>> We are going to have to agree to disagree on this one. Is it not
>>>>>> possible
>>>>>> that future drivers - e.g., when full virtualization is
>>>>>> implemented - will
>>>>>> require access to KVM?
>>>>>
>>>>> I do not think that an access to KVM is required for full
>>>>> virtualization.
>>>>
>>>> You may be right, but at this point, there is no guarantee. I stand
>>>> by my
>>>> design on this one.
>>>
>>> I really regret that we abandoned the initial design with the matrix
>>> bus and one
>>> single parent matrix device per guest.
>>> We would not have the problem of these KVM dependencies.
>>>
>>> It had the advantage of taking care of having only one device per guest
>>> (available_instance = 1), could take care of provisioning as you have
>>> sysfs entries available for a matrix without having a guest and a
>>> mediated
>>> device.
>>>
>>> it also had advantage for virtualization to keep host side and guest
>>> side matrix
>>> separate inside parent (host side) and mediated device (guest side).
>>>
>>> Shouldn't we treat this problem with a design using standard interfaces
>>> Instead of adding new dedicated interfaces?
>>>
>>> Regards,
>>>
>>> Pierre
>>>
>>>
>>
>> Forget it.
>>
>> I am not happy with the design but the design I was speaking of may
>> not be the solution either.
>
> The AP architecture makes virtualization of AP devices complex. We
> tried the solution you
> described and found it to be sorely lacking which is why we ended up
> where we are now.
I did not see any explanation on why between v1 and v2 as it was abandoned.
We have internal structures like the ap_matrix and kvm_ap_matrix
which look like the bus/devices we had previously but are differently
or not at all integrated with the LDD.
Also I think that with a little data structure refactoring you can avoid
most of
the code in the arch/s390/kvm.
For example, storing the kvm pointer inside the kvm_ap_matrix and
maintaining a list of the kvm_ap_matrix structures allows to easily know
if a guest already has an associated mediated device.
Pierre
>
>>
>>
>> Sorry for the noise.
>>
>> Regards,
>>
>> Pierre
>>
>>
>
--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany
next prev parent reply other threads:[~2018-06-07 15:20 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-07 15:11 [PATCH v5 00/13] s390: vfio-ap: guest dedicated crypto adapters Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 01/13] KVM: s390: Interface to test whether APXA installed Tony Krowiak
2018-05-16 10:21 ` Cornelia Huck
2018-05-16 10:45 ` Tony Krowiak
2018-05-17 9:11 ` Harald Freudenberger
2018-05-17 9:44 ` Cornelia Huck
2018-05-07 15:11 ` [PATCH v5 02/13] KVM: s390: refactor crypto initialization Tony Krowiak
2018-05-16 8:51 ` Pierre Morel
2018-05-16 11:14 ` Tony Krowiak
2018-05-16 12:17 ` Pierre Morel
2018-05-16 12:21 ` Cornelia Huck
2018-05-07 15:11 ` [PATCH v5 03/13] KVM: s390: CPU model support for AP virtualization Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 04/13] s390: vfio-ap: base implementation of VFIO AP device driver Tony Krowiak
2018-05-16 8:21 ` Pierre Morel
2018-05-16 11:29 ` Tony Krowiak
2018-05-16 11:45 ` Tony Krowiak
2018-06-07 8:57 ` Pierre Morel
2018-06-13 7:41 ` Pierre Morel
2018-06-13 7:48 ` Cornelia Huck
2018-06-13 10:54 ` Pierre Morel
2018-06-13 11:14 ` Cornelia Huck
2018-06-13 12:01 ` Pierre Morel
2018-06-13 12:12 ` Cornelia Huck
2018-06-13 12:16 ` Pierre Morel
2018-06-14 13:04 ` Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 05/13] s390: vfio-ap: register matrix device with VFIO mdev framework Tony Krowiak
2018-05-11 17:18 ` Halil Pasic
2018-05-14 19:42 ` Tony Krowiak
2018-05-15 14:17 ` Pierre Morel
2018-05-15 15:16 ` Tony Krowiak
2018-05-15 15:48 ` Halil Pasic
2018-05-15 16:11 ` Tony Krowiak
2018-05-17 7:44 ` Cornelia Huck
2018-05-21 15:13 ` Tony Krowiak
2018-05-22 8:19 ` Cornelia Huck
2018-05-22 21:41 ` Tony Krowiak
2018-05-16 10:42 ` Cornelia Huck
2018-05-16 12:48 ` Tony Krowiak
2018-05-16 12:58 ` Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 06/13] KVM: s390: interfaces to manage guest's AP matrix Tony Krowiak
2018-05-11 16:08 ` Halil Pasic
2018-05-16 14:29 ` Tony Krowiak
2018-05-16 14:41 ` Pierre Morel
2018-05-21 15:23 ` Tony Krowiak
2018-05-15 14:55 ` Pierre Morel
2018-05-15 16:07 ` Tony Krowiak
2018-05-16 7:48 ` Pierre Morel
2018-05-16 13:12 ` Tony Krowiak
2018-05-16 13:15 ` Pierre Morel
2018-05-16 13:48 ` Tony Krowiak
2018-05-18 8:55 ` Pierre Morel
2018-05-23 14:29 ` Tony Krowiak
2018-05-24 7:46 ` Pierre Morel
2018-05-07 15:11 ` [PATCH v5 07/13] s390: vfio-ap: sysfs interfaces to configure adapters Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 08/13] s390: vfio-ap: sysfs interfaces to configure domains Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 09/13] s390: vfio-ap: sysfs interfaces to configure control domains Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 10/13] s390: vfio-ap: sysfs interface to view matrix mdev matrix Tony Krowiak
2018-05-16 7:55 ` Pierre Morel
2018-05-23 14:38 ` Tony Krowiak
2018-05-24 9:10 ` Pierre Morel
2018-05-30 14:28 ` Tony Krowiak
2018-06-05 12:40 ` Pierre Morel
2018-06-06 14:24 ` Tony Krowiak
2018-06-06 15:10 ` Pierre Morel
2018-06-07 12:53 ` Tony Krowiak
2018-06-07 13:16 ` Halil Pasic
2018-06-07 14:33 ` Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 11/13] KVM: s390: implement mediated device open callback Tony Krowiak
2018-05-16 8:03 ` Pierre Morel
2018-05-23 14:45 ` Tony Krowiak
2018-05-24 9:08 ` Pierre Morel
2018-05-30 14:33 ` Tony Krowiak
2018-06-05 12:19 ` Pierre Morel
2018-06-06 14:28 ` Tony Krowiak
2018-06-06 16:08 ` Pierre Morel
2018-06-06 17:40 ` Pierre Morel
2018-06-07 13:54 ` Tony Krowiak
2018-06-07 15:20 ` Pierre Morel [this message]
2018-06-07 16:30 ` Tony Krowiak
2018-06-07 17:15 ` Pierre Morel
2018-06-08 21:59 ` Tony Krowiak
2018-06-11 9:23 ` Pierre Morel
2018-06-11 11:32 ` Halil Pasic
2018-06-11 11:49 ` Janosch Frank
2018-06-11 16:26 ` Tony Krowiak
2018-06-11 16:50 ` Halil Pasic
2018-06-11 16:54 ` Tony Krowiak
2018-06-11 12:50 ` Tony Krowiak
2018-06-11 12:56 ` Tony Krowiak
2018-06-07 13:52 ` Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 12/13] s390: vfio-ap: implement VFIO_DEVICE_GET_INFO ioctl Tony Krowiak
2018-05-07 15:11 ` [PATCH v5 13/13] s390: doc: detailed specifications for AP virtualization Tony Krowiak
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