[virtio-dev] Re: [PATCH 00/11] Introduce transitional mmr pci device

Michael S. Tsirkin
2023-04-12T05:12:17Z

On Wed, Apr 12, 2023 at 04:52:09AM +0000, Parav Pandit wrote:
>
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Wednesday, April 12, 2023 12:48 AM
>
> > Here is a counter proposal:
> >
> > #define VIRTIO_NET_F_LEGACY_HEADER 52 /* Use the legacy 10 byte
> > header for all packets */
> >
> >
> > Yes, sorry to say, you need to emulate legacy pci in software.
> >
> > With notification hacks, and reset hacks, and legacy interrupt hacks, and
> > writeable mac ... this thing best belongs in vdpa anyway.
>
> What? I don't follow.
> Suddenly you attribute everything as hack with least explanation.
>

Again hacks is not a bad thing but it's an attempt at reusing things in
unexpected ways.

New issue I found today:
- if guest disables MSI-X host can not disable MSI-X.
need some other channel to notify device about this.

Old issues we discussed before today:
- reset needs some special handling because real hardware
can not guarantee returning 0 on the 1st read
- if guest writes into mac, reusing host mac (which is RO)
will not work, need extra registers
- something about notification makes you want to poke
at modern notification register? which of course
is its own can of worms with VIRTIO_F_NOTIFICATION_DATA
changing the format completely.

--
MST