[dpdk-dev] [PATCH v3 7/9] net/virtio: Add MTU feature support

[Maxime Coquelin <maxime.coquelin@redhat.com>]

This patch implements support for the Virtio MTU feature.
When negotiated, the host shares its maximum supported MTU,
which is used as initial MTU and as maximum MTU the application
can set.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 doc/guides/nics/features/virtio.ini |  1 +
 drivers/net/virtio/virtio_ethdev.c  | 45 +++++++++++++++++++++++++++++++++++--
 drivers/net/virtio/virtio_ethdev.h  |  3 ++-
 drivers/net/virtio/virtio_pci.h     |  3 +++
 4 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/doc/guides/nics/features/virtio.ini b/doc/guides/nics/features/virtio.ini
index 84d2012..8e3aca1 100644
--- a/doc/guides/nics/features/virtio.ini
+++ b/doc/guides/nics/features/virtio.ini
@@ -25,3 +25,4 @@ ARMv8                = Y
 x86-32               = Y
 x86-64               = Y
 Usage doc            = Y
+MTU update           = Y
diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
index 4dc03b9..fd1213c 100644
--- a/drivers/net/virtio/virtio_ethdev.c
+++ b/drivers/net/virtio/virtio_ethdev.c
@@ -721,10 +721,13 @@ virtio_mtu_set(struct rte_eth_dev *dev, uint16_t mtu)
 	uint32_t ether_hdr_len = ETHER_HDR_LEN + VLAN_TAG_LEN +
 				 hw->vtnet_hdr_size;
 	uint32_t frame_size = mtu + ether_hdr_len;
+	uint32_t max_frame_size = hw->max_mtu + ether_hdr_len;
 
-	if (mtu < ETHER_MIN_MTU || frame_size > VIRTIO_MAX_RX_PKTLEN) {
+	max_frame_size = RTE_MIN(max_frame_size, VIRTIO_MAX_RX_PKTLEN);
+
+	if (mtu < ETHER_MIN_MTU || frame_size > max_frame_size) {
 		PMD_INIT_LOG(ERR, "MTU should be between %d and %d",
-			ETHER_MIN_MTU, VIRTIO_MAX_RX_PKTLEN - ether_hdr_len);
+			ETHER_MIN_MTU, max_frame_size - ether_hdr_len);
 		return -EINVAL;
 	}
 	return 0;
@@ -1158,6 +1161,18 @@ virtio_negotiate_features(struct virtio_hw *hw, uint64_t req_features)
 	PMD_INIT_LOG(DEBUG, "host_features before negotiate = %" PRIx64,
 		host_features);
 
+	/* If supported, ensure MTU value is valid before acknowledging it. */
+	if (host_features & req_features & (1ULL << VIRTIO_NET_F_MTU)) {
+		struct virtio_net_config config;
+
+		vtpci_read_dev_config(hw,
+			offsetof(struct virtio_net_config, mtu),
+			&config.mtu, sizeof(config.mtu));
+
+		if (config.mtu < ETHER_MIN_MTU)
+			req_features &= ~(1ULL << VIRTIO_NET_F_MTU);
+	}
+
 	/*
 	 * Negotiate features: Subset of device feature bits are written back
 	 * guest feature bits.
@@ -1392,6 +1407,32 @@ virtio_init_device(struct rte_eth_dev *eth_dev, uint64_t req_features)
 
 		hw->max_queue_pairs = config->max_virtqueue_pairs;
 
+		if (vtpci_with_feature(hw, VIRTIO_NET_F_MTU)) {
+			vtpci_read_dev_config(hw,
+				offsetof(struct virtio_net_config, mtu),
+				&config->mtu,
+				sizeof(config->mtu));
+
+			/*
+			 * MTU value has already been checked at negotiation
+			 * time, but check again in case it has changed since
+			 * then, which should not happen.
+			 */
+			if (config->mtu < ETHER_MIN_MTU) {
+				PMD_INIT_LOG(ERR, "invalid max MTU value (%u)",
+						config->mtu);
+				return -1;
+			}
+
+			hw->max_mtu = config->mtu;
+			/* Set initial MTU to maximum one supported by vhost */
+			eth_dev->data->mtu = config->mtu;
+
+		} else {
+			hw->max_mtu = VIRTIO_MAX_RX_PKTLEN - ETHER_HDR_LEN -
+				VLAN_TAG_LEN - hw->vtnet_hdr_size;
+		}
+
 		PMD_INIT_LOG(DEBUG, "config->max_virtqueue_pairs=%d",
 				config->max_virtqueue_pairs);
 		PMD_INIT_LOG(DEBUG, "config->status=%d", config->status);
diff --git a/drivers/net/virtio/virtio_ethdev.h b/drivers/net/virtio/virtio_ethdev.h
index 777a14b..aa78adc 100644
--- a/drivers/net/virtio/virtio_ethdev.h
+++ b/drivers/net/virtio/virtio_ethdev.h
@@ -51,7 +51,7 @@
 #define VIRTIO_MAX_TX_QUEUES 128U
 #define VIRTIO_MAX_MAC_ADDRS 64
 #define VIRTIO_MIN_RX_BUFSIZE 64
-#define VIRTIO_MAX_RX_PKTLEN  9728
+#define VIRTIO_MAX_RX_PKTLEN  9728U
 
 /* Features desired/implemented by this driver. */
 #define VIRTIO_PMD_DEFAULT_GUEST_FEATURES	\
@@ -66,6 +66,7 @@
 	 1u << VIRTIO_NET_F_HOST_TSO4	  |	\
 	 1u << VIRTIO_NET_F_HOST_TSO6	  |	\
 	 1u << VIRTIO_NET_F_MRG_RXBUF	  |	\
+	 1u << VIRTIO_NET_F_MTU	| \
 	 1u << VIRTIO_RING_F_INDIRECT_DESC |    \
 	 1ULL << VIRTIO_F_VERSION_1       |	\
 	 1ULL << VIRTIO_F_IOMMU_PLATFORM)
diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
index 59e45c4..771f5b1 100644
--- a/drivers/net/virtio/virtio_pci.h
+++ b/drivers/net/virtio/virtio_pci.h
@@ -106,6 +106,7 @@ struct virtnet_ctl;
 /* The feature bitmap for virtio net */
 #define VIRTIO_NET_F_CSUM	0	/* Host handles pkts w/ partial csum */
 #define VIRTIO_NET_F_GUEST_CSUM	1	/* Guest handles pkts w/ partial csum */
+#define VIRTIO_NET_F_MTU	3	/* Initial MTU advice. */
 #define VIRTIO_NET_F_MAC	5	/* Host has given MAC address. */
 #define VIRTIO_NET_F_GUEST_TSO4	7	/* Guest can handle TSOv4 in. */
 #define VIRTIO_NET_F_GUEST_TSO6	8	/* Guest can handle TSOv6 in. */
@@ -251,6 +252,7 @@ struct virtio_hw {
 	uint64_t    req_guest_features;
 	uint64_t    guest_features;
 	uint32_t    max_queue_pairs;
+	uint16_t	max_mtu;
 	uint16_t    vtnet_hdr_size;
 	uint8_t	    vlan_strip;
 	uint8_t	    use_msix;
@@ -296,6 +298,7 @@ struct virtio_net_config {
 	/* See VIRTIO_NET_F_STATUS and VIRTIO_NET_S_* above */
 	uint16_t   status;
 	uint16_t   max_virtqueue_pairs;
+	uint16_t   mtu;
 } __attribute__((packed));
 
 /*
-- 
2.9.3