git: aabdf5b6e8e8 - main - if_vtnet: Support VIRTIO_NET_F_MTU

[Bryan Venteicher]

The branch main has been updated by bryanv:

URL: https://cgit.FreeBSD.org/src/commit/?id=aabdf5b6e8e82cda0ca2064ef78e2724bd486e7e

commit aabdf5b6e8e82cda0ca2064ef78e2724bd486e7e
Author:     Bryan Venteicher <bryanv at FreeBSD.org>
AuthorDate: 2021-01-19 04:55:24 +0000
Commit:     Bryan Venteicher <bryanv at FreeBSD.org>
CommitDate: 2021-01-19 04:55:24 +0000

    if_vtnet: Support VIRTIO_NET_F_MTU
    
    This feature lets the guest driver know the maximum MTU size
    supported by the host device. If set, use this to limit the
    acceptable MTUs, and improve how the receive mbuf cluster size
    then is selected.
    
    Reviewed by: grehan (mentor)
    Differential Revision: https://reviews.freebsd.org/D27907
---
 sys/dev/virtio/network/if_vtnet.c    | 15 ++++++++++-----
 sys/dev/virtio/network/if_vtnetvar.h |  2 ++
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/sys/dev/virtio/network/if_vtnet.c b/sys/dev/virtio/network/if_vtnet.c
index d90fd3bc43aa..ca60e51c57d2 100644
--- a/sys/dev/virtio/network/if_vtnet.c
+++ b/sys/dev/virtio/network/if_vtnet.c
@@ -668,6 +668,12 @@ vtnet_setup_features(struct vtnet_softc *sc)
 		sc->vtnet_flags |= VTNET_FLAG_MAC;
 	}
 
+	if (virtio_with_feature(dev, VIRTIO_NET_F_MTU)) {
+		sc->vtnet_max_mtu = virtio_read_dev_config_2(dev,
+		    offsetof(struct virtio_net_config, mtu));
+	} else
+		sc->vtnet_max_mtu = VTNET_MAX_MTU;
+
 	if (virtio_with_feature(dev, VIRTIO_NET_F_MRG_RXBUF)) {
 		sc->vtnet_flags |= VTNET_FLAG_MRG_RXBUFS;
 		sc->vtnet_hdr_size = sizeof(struct virtio_net_hdr_mrg_rxbuf);
@@ -1094,10 +1100,9 @@ vtnet_rx_cluster_size(struct vtnet_softc *sc, int mtu)
 		return (MCLBYTES);
 
 	/*
-	 * Try to scale the receive mbuf cluster size from the MTU. Without
-	 * the GUEST_TSO[46] features, the VirtIO specification says the
-	 * driver must only be able to receive ~1500 byte frames. But if
-	 * jumbo frames can be transmitted then try to receive jumbo.
+	 * Try to scale the receive mbuf cluster size from the MTU. We
+	 * could also use the VQ size to influence the selected size,
+	 * but that would only matter for very small queues.
 	 */
 	if (vtnet_modern(sc)) {
 		MPASS(sc->vtnet_hdr_size == sizeof(struct virtio_net_hdr_v1));
@@ -1128,7 +1133,7 @@ vtnet_ioctl_mtu(struct vtnet_softc *sc, int mtu)
 
 	if (ifp->if_mtu == mtu)
 		return (0);
-	else if (mtu < ETHERMIN || mtu > VTNET_MAX_MTU)
+	else if (mtu < ETHERMIN || mtu > sc->vtnet_max_mtu)
 		return (EINVAL);
 
 	ifp->if_mtu = mtu;
diff --git a/sys/dev/virtio/network/if_vtnetvar.h b/sys/dev/virtio/network/if_vtnetvar.h
index eaf6eaf8d504..29a0dbbb734f 100644
--- a/sys/dev/virtio/network/if_vtnetvar.h
+++ b/sys/dev/virtio/network/if_vtnetvar.h
@@ -164,6 +164,7 @@ struct vtnet_softc {
 	int			 vtnet_tx_intr_thresh;
 	int			 vtnet_tx_nsegs;
 	int			 vtnet_if_flags;
+	int			 vtnet_max_mtu;
 	int			 vtnet_act_vq_pairs;
 	int			 vtnet_max_vq_pairs;
 	int			 vtnet_requested_vq_pairs;
@@ -297,6 +298,7 @@ CTASSERT(sizeof(struct vtnet_mac_filter) <= PAGE_SIZE);
 #define VTNET_COMMON_FEATURES \
     (VIRTIO_NET_F_MAC			| \
      VIRTIO_NET_F_STATUS		| \
+     VIRTIO_NET_F_MTU			| \
      VIRTIO_NET_F_CTRL_VQ		| \
      VIRTIO_NET_F_CTRL_RX		| \
      VIRTIO_NET_F_CTRL_MAC_ADDR		| \