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

[David Hildenbrand]

On 07.04.25 10:44, Michael S. Tsirkin wrote:
> Wow great job digging through all these hypervisors!
>
> On Mon, Apr 07, 2025 at 10:38:59AM +0200, David Hildenbrand wrote:
> > crossvm:
> > https://github.com/google/crosvm/blob/main/devices/src/virtio/balloon.rs
> >
> > -> Hard-codes queue numbers; does *not* offer/implement
> >     VIRTIO_BALLOON_F_STATS_VQ but does offer VIRTIO_BALLOON_F_STATS_VQ
> >     and VIRTIO_BALLOON_F_DEFLATE_ON_OOM.
> >
> > -> Implements something that is not in the virtio-spec
> >
> > const VIRTIO_BALLOON_F_WS_REPORTING: u32 = 8; // Working Set Reporting
> > virtqueues
> >
> > and
> >
> > const WS_DATA_VQ: usize = 5;
> > const WS_OP_VQ: usize = 6;
> >
> >
> > IIUC, Linux inside cross-vm might actually be problematic? They would
> > disagree on the virtqueue for free-page-reporting
>
>
> That's why things must be tied to negotiated features, not to offered
> ones.

cross-vm also has this weird comment:

"
const VIRTIO_BALLOON_F_PAGE_REPORTING: u32 = 5; // Page reporting virtqueue
                                                // TODO(b/273973298): 
this should maybe be bit 6? to be changed later
"

Not sure why that should be bit 6, the spec says 5 ...

So maybe whatever they run inside the VM is also out of spec ... Really 
hard to tell.

--
Cheers,

David / dhildenb