Re: [PATCH] virtio-net: not enable vq reset feature unconditionally

[Eugenio Perez Martin]

On Sat, May 6, 2023 at 4:25 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Thu,  4 May 2023 12:14:47 +0200, =?utf-8?q?Eugenio_P=C3=A9rez?= 
> <eperezma@redhat.com> wrote:
> > The commit 93a97dc5200a ("virtio-net: enable vq reset feature") enables
> > unconditionally vq reset feature as long as the device is emulated.
> > This makes impossible to actually disable the feature, and it causes
> > migration problems from qemu version previous than 7.2.
> >
> > The entire final commit is unneeded as device system already enable or
> > disable the feature properly.
> >
> > This reverts commit 93a97dc5200a95e63b99cb625f20b7ae802ba413.
> > Fixes: 93a97dc5200a ("virtio-net: enable vq reset feature")
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> >
> > ---
> > Tested by checking feature bit at  /sys/devices/pci.../virtio0/features
> > enabling and disabling queue_reset virtio-net feature and vhost=on/off
> > on net device backend.
>
> Do you mean that this feature cannot be closed?
>
> I tried to close in the guest, it was successful.
>

I'm not sure what you mean with close. If the device dataplane is
emulated in qemu (vhost=off), I'm not able to make the device not
offer it.

> In addition, in this case, could you try to repair the problem instead of
> directly revert.
>

I'm not following this. The revert is not to always disable the feature.

By default, the feature is enabled. If cmdline states queue_reset=on,
the feature is enabled. That is true both before and after applying
this patch.

However, in qemu master, queue_reset=off keeps enabling this feature
on the device. It happens that there is a commit explicitly doing
that, so I'm reverting it.

Let me know if that makes sense to you.

Thanks!