Re: [PATCH] vhost-vdpa: filter VIRTIO_F_RING_PACKED feature

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On Mon, Jun 05, 2023 at 09:00:25AM -0400, Michael S. Tsirkin wrote:
On Mon, Jun 05, 2023 at 02:54:20PM +0200, Stefano Garzarella wrote:
On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S. Tsirkin wrote:
> On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano Garzarella wrote:
> > don't support packed virtqueue well yet, so let's filter the
> > VIRTIO_F_RING_PACKED feature for now in vhost_vdpa_get_features().
> >
> > This way, even if the device supports it, we don't risk it being
> > negotiated, then the VMM is unable to set the vring state properly.
> >
> > Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> > ---
> >
> > Notes:
> >     This patch should be applied before the "[PATCH v2 0/3] vhost_vdpa:
> >     better PACKED support" series [1] and backported in stable branches.
> >
> >     We can revert it when we are sure that everything is working with
> >     packed virtqueues.
> >
> >     Thanks,
> >     Stefano
> >
> >     [1]
> I'm a bit lost here. So why am I merging "better PACKED support" then?

To really support packed virtqueue with vhost-vdpa, at that point we would
also have to revert this patch.

I wasn't sure if you wanted to queue the series for this merge window.
In that case do you think it is better to send this patch only for stable
> Does this patch make them a NOP?

Yep, after applying the "better PACKED support" series and being sure that
the IOCTLs of vhost-vdpa support packed virtqueue, we should revert this

Let me know if you prefer a different approach.

I'm concerned that QEMU uses vhost-vdpa IOCTLs thinking that the kernel
interprets them the right way, when it does not.


If this fixes a bug can you add Fixes tags to each of them? Then it's ok
to merge in this window. Probably easier than the elaborate
mask/unmask dance.

CCing Shannon (the original author of the "better PACKED support"

IIUC Shannon is going to send a v3 of that series to fix the
documentation, so Shannon can you also add the Fixes tags?


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