Linux Virtualization - Apr 2023 - [PATCH net] virtio-net: reject small vring sizes

On Mon, 17 Apr 2023 06:38:43 +0000, Alvaro Karsz <alvaro.karsz at
solid-run.com> wrote:
> > Actually, I think that all you need to do is disable NETIF_F_SG,
> > and things will work, no?
>
> I think that this is not so simple, if I understand correctly, by disabling
NETIF_F_SG we will never receive a chained skbs to transmit, but we still have
more functionality to address, for example:
> * The TX timeouts.
Why tx timeout without frags?
> * Guest GSO/big MTU (without VIRTIO_NET_F_MRG_RXBUF?), we can't chain
page size buffers anymore.

Or, we disable the GUEST_GSO, HOST_GSO......

Thanks.
>
> > Alvaro, can you try?
>
> It won't matter at the moment, we'll get TX timeout after the first
tx packet, we need to address this part as well.

> Why tx timeout without frags?
Please see my response to Michael.
> > * Guest GSO/big MTU (without VIRTIO_NET_F_MRG_RXBUF?), we can't
chain page size buffers anymore.
> 
> 
> Or, we disable the GUEST_GSO, HOST_GSO......
> 
And disable VIRTIO_NET_F_MTU, quoting the spec:
"A driver SHOULD negotiate VIRTIO_NET_F_MTU if the device offers it."

We can find a way around using buffers bigger than a page size like Michael
implied.