linux-kernel - Re: [PATCH v1] s390/virtio_ccw: don't allocate/assign airqs for non-existing queues

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Message-ID: <33def1b0-d9d5-46f1-9b61-b0269753ecce@redhat.com>
Date: Mon, 7 Apr 2025 11:13:43 +0200
From: David Hildenbrand <david@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Halil Pasic <pasic@...ux.ibm.com>, linux-kernel@...r.kernel.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 kvm@...r.kernel.org, Chandra Merla <cmerla@...hat.com>,
 Stable@...r.kernel.org, Cornelia Huck <cohuck@...hat.com>,
 Thomas Huth <thuth@...hat.com>, Eric Farman <farman@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Wei Wang <wei.w.wang@...el.com>
Subject: Re: [PATCH v1] s390/virtio_ccw: don't allocate/assign airqs for
 non-existing queues

On 07.04.25 11:11, David Hildenbrand wrote:
> On 07.04.25 10:58, Michael S. Tsirkin wrote:
>> On Mon, Apr 07, 2025 at 10:54:00AM +0200, David Hildenbrand wrote:
>>> On 07.04.25 10:49, Michael S. Tsirkin wrote:
>>>> On Mon, Apr 07, 2025 at 10:44:21AM +0200, David Hildenbrand wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>>> Whoever adds new feat_X *must be aware* about all previous features,
>>>>>>> otherwise we'd be reusing feature bits and everything falls to pieces.
>>>>>>
>>>>>>
>>>>>> The knowledge is supposed be limited to which feature bit to use.
>>>>>
>>>>> I think we also have to know which virtqueue bits can be used, right?
>>>>>
>>>>
>>>> what are virtqueue bits? vq number?
>>>
>>> Yes, sorry.
>>
>> I got confused myself, it's vq index actually now, we made the spec
>> consistent with that terminology. used to be number/index
>> interchangeably.
>>
>>> Assume cross-vm as an example. It would make use of virtqueue indexes 5+6
>>> with their VIRTIO_BALLOON_F_WS_REPORTING.
>>
>>
>> crossvm guys really should have reserved the feature bit even if they
>> did not bother specifying it. Let's reserve it now at least?
> 
> Along with the virtqueue indices, right?
> 
> Note that there was
> 
> https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg02503.html
> 
> and
> 
> https://groups.oasis-open.org/communities/community-home/digestviewer/viewthread?GroupId=3973&MessageKey=afb07613-f56c-4d40-8981-2fad1c723998&CommunityKey=2f26be99-3aa1-48f6-93a5-018dce262226&hlmlt=VT
> 
> But it only was RFC, and as the QEMU implementation didn't materialize,
> nobody seemed to care ...

Heh, but that one said:

+\item[ VIRTIO_BALLOON_F_WS_REPORTING(6) ] The device has support for
Working Set

Which does not seem to reflect reality ...

-- 
Cheers,

David / dhildenb