linux-kernel - Re: [PATCH 1/4] virtio-net: add definitions for host USO feature

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Date:   Tue, 11 May 2021 12:21:04 +0300
From:   Yuri Benditovich <yuri.benditovich@...nix.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        Yan Vugenfirer <yan@...nix.com>
Subject: Re: [PATCH 1/4] virtio-net: add definitions for host USO feature

On Tue, May 11, 2021 at 11:24 AM Jason Wang <jasowang@...hat.com> wrote:
>
> On Tue, May 11, 2021 at 4:12 PM Yuri Benditovich
> <yuri.benditovich@...nix.com> wrote:
> >
> > On Tue, May 11, 2021 at 9:47 AM Jason Wang <jasowang@...hat.com> wrote:
> > >
> > >
> > > 在 2021/5/11 下午12:42, Yuri Benditovich 写道:
> > > > Define feature bit and GSO type according to the VIRTIO
> > > > specification.
> > > >
> > > > Signed-off-by: Yuri Benditovich <yuri.benditovich@...nix.com>
> > > > ---
> > > >   include/uapi/linux/virtio_net.h | 2 ++
> > > >   1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h
> > > > index 3f55a4215f11..a556ac735d7f 100644
> > > > --- a/include/uapi/linux/virtio_net.h
> > > > +++ b/include/uapi/linux/virtio_net.h
> > > > @@ -57,6 +57,7 @@
> > > >                                        * Steering */
> > > >   #define VIRTIO_NET_F_CTRL_MAC_ADDR 23       /* Set MAC address */
> > > >
> > > > +#define VIRTIO_NET_F_HOST_USO     56 /* Host can handle USO packets */
> >
> > This is the virtio-net feature
>
> Right, I miss this part.
>
> >
> > > >   #define VIRTIO_NET_F_HASH_REPORT  57        /* Supports hash report */
> > > >   #define VIRTIO_NET_F_RSS      60    /* Supports RSS RX steering */
> > > >   #define VIRTIO_NET_F_RSC_EXT          61    /* extended coalescing info */
> > > > @@ -130,6 +131,7 @@ struct virtio_net_hdr_v1 {
> > > >   #define VIRTIO_NET_HDR_GSO_TCPV4    1       /* GSO frame, IPv4 TCP (TSO) */
> > > >   #define VIRTIO_NET_HDR_GSO_UDP              3       /* GSO frame, IPv4 UDP (UFO) */
> > > >   #define VIRTIO_NET_HDR_GSO_TCPV6    4       /* GSO frame, IPv6 TCP */
> > > > +#define VIRTIO_NET_HDR_GSO_UDP_L4    5       /* GSO frame, IPv4 UDP (USO) */
> >
> > This is respective GSO type
> >
> > >
> > >
> > > This is the gso_type not the feature actually.
> > >
> > > I wonder what's the reason for not
> > >
> > > 1) introducing a dedicated virtio-net feature bit for this
> > > (VIRTIO_NET_F_GUEST_GSO_UDP_L4.
> >
> > This series is not for GUEST's feature, it is only for host feature.
> >
> > > 2) toggle the NETIF_F_GSO_UDP_L4  feature for tuntap based on the
> > > negotiated feature.
> >
> > The NETIF_F_GSO_UDP_L4 would be required for the guest RX path.
> > The guest TX path does not require any flags to be propagated, it only
> > allows the guest to transmit large UDP packets and have them
> > automatically splitted.
> > (This is similar to HOST_UFO but does packet segmentation instead of
> > fragmentation. GUEST_UFO indeed requires a respective NETIF flag, as
> > it is unclear whether the guest is capable of receiving such packets).
>
> So I think it's better to implement TX/RX in the same series unless
> there's something missed:
>
> For Guest TX, NETIF_F_GSO_UDP_L4 needs to be enabled in the guest
> virtio-net only when VIRTIO_NET_F_HOST_USO is negotiated.

I understand that this is what should be done when this feature will
be added to Linux virtio-net driver.
But at the moment we do not have enough resources to work on it.
Currently we have a clear use case and ability to test in on Windows guest.
Respective QEMU changes are pending for kernel patches, current
reference is https://github.com/daynix/qemu/tree/uso

> For guest RX, NETIF_F_GSO_UDP_L4 needs to be enabled on the host
> tuntap only when VIRTIO_NET_F_GUEST_USO is neogiated.

Currently we are not able to use guest RX UDP GSO.
In order to do that we at least should be able to build our Windows
drivers with the most updated driver development kit (2004+).
At the moment we can't, this task is in a plan but can take several
months. So we do not have a test/use case with Windows VM.


>
> Thanks
>
> >
> > >
> > > Thanks
> > >
> > >
> > > >   #define VIRTIO_NET_HDR_GSO_ECN              0x80    /* TCP has ECN set */
> > > >       __u8 gso_type;
> > > >       __virtio16 hdr_len;     /* Ethernet + IP + tcp/udp hdrs */
> > >
> >
>