[PATCH] net/gve: advertise Rx scatter in GQI queue format

[PATCH] net/gve: advertise Rx scatter in GQI queue format

[Ryan Wolfe]

Since jumbo frame support for GQI, a frame that does not fit in one Rx
buffer arrives as several descriptors with GVE_RXF_PKT_CONT set on all
but the last, and gve_rx_burst() chains them into one multi-segment
mbuf. The driver never reports RTE_ETH_RX_OFFLOAD_SCATTER, though, so
an application that enables multi-segment receive only when the port
claims it treats every packet as one segment. VPP is one: it masks its
requested Rx offloads with rx_offload_capa, so on a GQI gVNIC it never
sets its multi-segment flag, reads only the first buffer of a jumbo
frame and drops it as malformed. With 4 KB buffers that caps the usable
MTU near 4000 bytes on a VPC whose MTU is 8896.

Report SCATTER for GQI. DQO posts one buffer per packet and does not
chain, so it is unchanged.

Fixes: 496d4d2c8b54 ("net/gve: support jumbo frame for GQI")
Cc: stable@dpdk.org

Signed-off-by: Ryan Wolfe <rnwolfe@google.com>
---
 .mailmap                         | 1 +
 doc/guides/nics/features/gve.ini | 1 +
 drivers/net/gve/gve_ethdev.c     | 5 +++++
 3 files changed, 7 insertions(+)

diff --git a/.mailmap b/.mailmap
index 6d9e262cfb..87c544947c 100644
--- a/.mailmap
+++ b/.mailmap
@@ -1477,6 +1477,7 @@ Ruifeng Wang <ruifeng.wang@arm.com>
 Rupesh Chiluka <rchiluka@marvell.com>
 Rushil Gupta <rushilg@google.com>
 Ryan E Hall <ryan.e.hall@intel.com>
+Ryan Wolfe <rnwolfe@google.com>
 Sabyasachi Sengupta <sabyasg@hpe.com>
 Sachin Saxena <sachin.saxena@nxp.com> <sachin.saxena@oss.nxp.com>
 Sagar Abhang <sabhang@brocade.com>
diff --git a/doc/guides/nics/features/gve.ini b/doc/guides/nics/features/gve.ini
index 9f3835edf6..5566511b6b 100644
--- a/doc/guides/nics/features/gve.ini
+++ b/doc/guides/nics/features/gve.ini
@@ -7,6 +7,7 @@
 Speed capabilities   = Y
 Queue start/stop     = Y
 MTU update           = Y
+Scattered Rx         = P
 TSO                  = Y
 RSS hash             = Y
 RSS key update       = Y
diff --git a/drivers/net/gve/gve_ethdev.c b/drivers/net/gve/gve_ethdev.c
index 3c8d1a76e4..92a5a7679f 100644
--- a/drivers/net/gve/gve_ethdev.c
+++ b/drivers/net/gve/gve_ethdev.c
@@ -897,6 +897,11 @@ gve_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	dev_info->min_mtu = RTE_ETHER_MIN_MTU;
 
 	dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_RSS_HASH;
+	/* GQI receives a frame larger than one Rx buffer as a chain of
+	 * buffers (gve_rx_burst follows GVE_RXF_PKT_CONT).
+	 */
+	if (gve_is_gqi(priv))
+		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_SCATTER;
 	if (priv->clk_read_type != GVE_DEV_CLK_UNSUPPORTED &&
 	    priv->nic_ts_report_mz != NULL)
 		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_TIMESTAMP;

Re: [PATCH] net/gve: advertise Rx scatter in GQI queue format

[Stephen Hemminger]

On Sun, 18 Oct 2026 22:28:24 -0400
Ryan Wolfe <rnwolfe@google.com> wrote:

> Since jumbo frame support for GQI, a frame that does not fit in one Rx
> buffer arrives as several descriptors with GVE_RXF_PKT_CONT set on all
> but the last, and gve_rx_burst() chains them into one multi-segment
> mbuf. The driver never reports RTE_ETH_RX_OFFLOAD_SCATTER, though, so
> an application that enables multi-segment receive only when the port
> claims it treats every packet as one segment. VPP is one: it masks its
> requested Rx offloads with rx_offload_capa, so on a GQI gVNIC it never
> sets its multi-segment flag, reads only the first buffer of a jumbo
> frame and drops it as malformed. With 4 KB buffers that caps the usable
> MTU near 4000 bytes on a VPC whose MTU is 8896.
> 
> Report SCATTER for GQI. DQO posts one buffer per packet and does not
> chain, so it is unchanged.
> 
> Fixes: 496d4d2c8b54 ("net/gve: support jumbo frame for GQI")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Ryan Wolfe <rnwolfe@google.com>
> ---
Subject: Re: [PATCH] net/gve: advertise Rx scatter in GQI queue format

Applies to main and builds with -Dwerror=true. The Fixes hash
resolves.

Warnings

1. GQI chains buffers whether or not the application enabled scatter.

   With this patch an application can request
   RTE_ETH_RX_OFFLOAD_SCATTER, but gve_rx() follows GVE_RXF_PKT_CONT
   regardless, so one that does not still gets multi-segment mbufs
   whenever the MTU exceeds the Rx buffer. Advertising the capability
   is only half the contract; without SCATTER the driver must refuse
   the configuration rather than hand back chains the application
   did not ask for. Check it in gve_rx_queue_setup() before the rxq
   allocation:

       uint64_t offloads = dev->data->dev_conf.rxmode.offloads |
                           conf->offloads;
       uint32_t buf_len = RTE_MIN((uint32_t)GVE_RX_MAX_BUF_SIZE_GQI,
               RTE_ALIGN_FLOOR(rte_pktmbuf_data_room_size(pool) -
                               RTE_PKTMBUF_HEADROOM,
                               GVE_RX_BUF_ALIGN_GQI));

       if (!(offloads & RTE_ETH_RX_OFFLOAD_SCATTER) &&
           dev->data->mtu + RTE_ETHER_HDR_LEN + GVE_RX_PAD > buf_len) {
               PMD_DRV_LOG(ERR, "MTU %u needs Rx scatter",
                           dev->data->mtu);
               return -EINVAL;
       }

   and apply the same test in gve_dev_mtu_set() against the configured
   Rx queues, since the MTU can change after queue setup. A separate
   patch in the same series is fine.

Info

2. The commit message says DQO "does not chain, so it is unchanged".
   DQO Rx ignores end_of_packet, so with buffers smaller than the
   frame (2 KB mbufs, 8896 MTU) each buffer is delivered as its own
   packet. Not introduced here, but DQO should either chain or refuse
   that configuration too.

[PATCH v2 0/2] net/gve: Rx scatter for GQI

[Ryan Wolfe]

GQI receives a frame larger than one Rx buffer as a chain of mbufs, but
the driver doesn't report RTE_ETH_RX_OFFLOAD_SCATTER, and it chains
whether or not the application enabled it. 1/2 reports SCATTER for GQI
so an application that gates multi-segment receive on the capability,
such as VPP, can turn it on. 2/2 refuses an Rx queue setup or an MTU
change that would need scatter when the application hasn't enabled it.

Both patches change only the GQI queue format. DQO has a related
problem that this series leaves alone: its Rx path ignores
end_of_packet, so with Rx buffers smaller than the frame each buffer
is delivered as its own packet. DQO should either chain those buffers
or refuse that configuration too; that is left for a follow-up.

One more gap 2/2 doesn't close: the check reads dev->data->mtu, but gve
never pushes that value to the device. rte_eth_dev_configure() sets it
without calling mtu_set, so an application that never calls
rte_eth_dev_set_mtu() passes the check at 1500 while the device keeps
the MTU from its device descriptor, and on a jumbo VPC it can still get
chained frames. Applying dev->data->mtu at configure or start would fix
that but changes behavior and needs hardware to test, so it is left for
the same follow-up.

v2:
- add 2/2 to refuse MTUs that need scatter when it isn't enabled
  (Stephen)
- correct the DQO statement in 1/2

Ryan Wolfe (2):
  net/gve: advertise Rx scatter in GQI queue format
  net/gve: refuse an MTU that needs Rx scatter when it is off

 .mailmap                         |  1 +
 doc/guides/nics/features/gve.ini |  1 +
 drivers/net/gve/gve_ethdev.c     | 23 +++++++++++++++++++++++
 drivers/net/gve/gve_ethdev.h     |  9 +++++++++
 drivers/net/gve/gve_rx.c         | 31 +++++++++++++++++++++++++------
 5 files changed, 59 insertions(+), 6 deletions(-)

-- 
2.56.0.218.g1ec904b173-goog

[PATCH v2 1/2] net/gve: advertise Rx scatter in GQI queue format

[Ryan Wolfe]

Since jumbo frame support for GQI, a frame that does not fit in one Rx
buffer arrives as several descriptors with GVE_RXF_PKT_CONT set on all
but the last, and gve_rx_burst() chains them into one multi-segment
mbuf. The driver never reports RTE_ETH_RX_OFFLOAD_SCATTER, though, so
an application that enables multi-segment receive only when the port
claims it treats every packet as one segment. VPP is one: it masks its
requested Rx offloads with rx_offload_capa, so on a GQI gVNIC it never
sets its multi-segment flag, reads only the first buffer of a jumbo
frame and drops it as malformed. With 4 KB buffers that caps the usable
MTU near 4000 bytes on a VPC whose MTU is 8896.

Report SCATTER for GQI only. The DQO Rx path is not touched by this
patch.

Fixes: 496d4d2c8b54 ("net/gve: support jumbo frame for GQI")
Cc: stable@dpdk.org

Signed-off-by: Ryan Wolfe <rnwolfe@google.com>
---
 .mailmap                         | 1 +
 doc/guides/nics/features/gve.ini | 1 +
 drivers/net/gve/gve_ethdev.c     | 5 +++++
 3 files changed, 7 insertions(+)

diff --git a/.mailmap b/.mailmap
index 6d9e262cfb..87c544947c 100644
--- a/.mailmap
+++ b/.mailmap
@@ -1477,6 +1477,7 @@ Ruifeng Wang <ruifeng.wang@arm.com>
 Rupesh Chiluka <rchiluka@marvell.com>
 Rushil Gupta <rushilg@google.com>
 Ryan E Hall <ryan.e.hall@intel.com>
+Ryan Wolfe <rnwolfe@google.com>
 Sabyasachi Sengupta <sabyasg@hpe.com>
 Sachin Saxena <sachin.saxena@nxp.com> <sachin.saxena@oss.nxp.com>
 Sagar Abhang <sabhang@brocade.com>
diff --git a/doc/guides/nics/features/gve.ini b/doc/guides/nics/features/gve.ini
index 9f3835edf6..5566511b6b 100644
--- a/doc/guides/nics/features/gve.ini
+++ b/doc/guides/nics/features/gve.ini
@@ -7,6 +7,7 @@
 Speed capabilities   = Y
 Queue start/stop     = Y
 MTU update           = Y
+Scattered Rx         = P
 TSO                  = Y
 RSS hash             = Y
 RSS key update       = Y
diff --git a/drivers/net/gve/gve_ethdev.c b/drivers/net/gve/gve_ethdev.c
index 3c8d1a76e4..92a5a7679f 100644
--- a/drivers/net/gve/gve_ethdev.c
+++ b/drivers/net/gve/gve_ethdev.c
@@ -897,6 +897,11 @@ gve_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
 	dev_info->min_mtu = RTE_ETHER_MIN_MTU;
 
 	dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_RSS_HASH;
+	/* GQI receives a frame larger than one Rx buffer as a chain of
+	 * buffers (gve_rx_burst follows GVE_RXF_PKT_CONT).
+	 */
+	if (gve_is_gqi(priv))
+		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_SCATTER;
 	if (priv->clk_read_type != GVE_DEV_CLK_UNSUPPORTED &&
 	    priv->nic_ts_report_mz != NULL)
 		dev_info->rx_offload_capa |= RTE_ETH_RX_OFFLOAD_TIMESTAMP;
-- 
2.56.0.218.g1ec904b173-goog

[PATCH v2 2/2] net/gve: refuse an MTU that needs Rx scatter when it is off

[Ryan Wolfe]

GQI chains a frame larger than one Rx buffer into a multi-segment mbuf
whether or not the application enabled RTE_ETH_RX_OFFLOAD_SCATTER, so
an application that did not ask for scatter can still receive chained
mbufs once the MTU exceeds the Rx buffer.

Refuse such a configuration on GQI. Rx queue setup fails when the
current MTU plus the Ethernet header and the GVE_RX_PAD bytes ahead of
the frame does not fit in the queue's Rx buffer, and an MTU change
fails on the same test against each configured Rx queue. The buffer
length comes from one helper shared with queue setup, so the check
matches the size the device is given. DQO is unchanged.

Fixes: 496d4d2c8b54 ("net/gve: support jumbo frame for GQI")
Cc: stable@dpdk.org

Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Ryan Wolfe <rnwolfe@google.com>
---
 drivers/net/gve/gve_ethdev.c | 18 ++++++++++++++++++
 drivers/net/gve/gve_ethdev.h |  9 +++++++++
 drivers/net/gve/gve_rx.c     | 31 +++++++++++++++++++++++++------
 3 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/drivers/net/gve/gve_ethdev.c b/drivers/net/gve/gve_ethdev.c
index 92a5a7679f..e47ec0c55b 100644
--- a/drivers/net/gve/gve_ethdev.c
+++ b/drivers/net/gve/gve_ethdev.c
@@ -1031,6 +1031,24 @@ gve_dev_mtu_set(struct rte_eth_dev *dev, uint16_t mtu)
 		return -EBUSY;
 	}
 
+	/* GQI chains a frame larger than one Rx buffer into a multi-segment
+	 * mbuf. No Rx offload is per-queue here, so check the port offloads.
+	 */
+	if (gve_is_gqi(priv) &&
+	    !(dev->data->dev_conf.rxmode.offloads & RTE_ETH_RX_OFFLOAD_SCATTER)) {
+		for (uint16_t i = 0; i < dev->data->nb_rx_queues; i++) {
+			struct gve_rx_queue *rxq = dev->data->rx_queues[i];
+
+			if (rxq != NULL &&
+			    gve_rx_gqi_needs_scatter(mtu, rxq->rx_buf_len)) {
+				PMD_DRV_LOG(ERR,
+					    "MTU %u needs Rx scatter with %u byte Rx buffers",
+					    mtu, rxq->rx_buf_len);
+				return -EINVAL;
+			}
+		}
+	}
+
 	err = process_priv->ctrl_ops->set_mtu(priv, mtu);
 	if (err) {
 		PMD_DRV_LOG(ERR, "Failed to set mtu as %u err = %d", mtu, err);
diff --git a/drivers/net/gve/gve_ethdev.h b/drivers/net/gve/gve_ethdev.h
index 19eac9ec0b..f4b72a9159 100644
--- a/drivers/net/gve/gve_ethdev.h
+++ b/drivers/net/gve/gve_ethdev.h
@@ -454,6 +454,15 @@ gve_is_gqi(struct gve_priv *priv)
 		priv->queue_format == GVE_GQI_QPL_FORMAT;
 }
 
+/* GQI places GVE_RX_PAD bytes ahead of the frame in its first Rx buffer
+ * and chains the rest of a larger frame into further buffers.
+ */
+static inline bool
+gve_rx_gqi_needs_scatter(uint16_t mtu, uint16_t rx_buf_len)
+{
+	return (uint32_t)mtu + RTE_ETHER_HDR_LEN + GVE_RX_PAD > rx_buf_len;
+}
+
 static inline bool
 gve_get_admin_queue_ok(struct gve_priv *priv)
 {
diff --git a/drivers/net/gve/gve_rx.c b/drivers/net/gve/gve_rx.c
index 09f9d8d480..4a455b3067 100644
--- a/drivers/net/gve/gve_rx.c
+++ b/drivers/net/gve/gve_rx.c
@@ -297,6 +297,16 @@ gve_rx_queue_release(struct rte_eth_dev *dev, uint16_t qid)
 	dev->data->rx_queues[qid] = NULL;
 }
 
+static uint16_t
+gve_rx_buf_len_gqi(struct rte_mempool *pool)
+{
+	uint32_t mbuf_len =
+		rte_pktmbuf_data_room_size(pool) - RTE_PKTMBUF_HEADROOM;
+
+	return RTE_MIN((uint16_t)GVE_RX_MAX_BUF_SIZE_GQI,
+		       RTE_ALIGN_FLOOR(mbuf_len, GVE_RX_BUF_ALIGN_GQI));
+}
+
 int
 gve_rx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_id,
 		uint16_t nb_desc, unsigned int socket_id,
@@ -306,7 +316,8 @@ gve_rx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_id,
 	const struct rte_memzone *mz;
 	struct gve_rx_queue *rxq;
 	uint16_t free_thresh;
-	uint32_t mbuf_len;
+	uint16_t rx_buf_len;
+	uint64_t offloads;
 	int err = 0;
 
 	/* Ring size is required to be a power of two. */
@@ -316,6 +327,18 @@ gve_rx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_id,
 		return -EINVAL;
 	}
 
+	/* A frame larger than one Rx buffer is chained into a multi-segment
+	 * mbuf, which the application must have asked for.
+	 */
+	offloads = dev->data->dev_conf.rxmode.offloads | conf->offloads;
+	rx_buf_len = gve_rx_buf_len_gqi(pool);
+	if (!(offloads & RTE_ETH_RX_OFFLOAD_SCATTER) &&
+	    gve_rx_gqi_needs_scatter(dev->data->mtu, rx_buf_len)) {
+		PMD_DRV_LOG(ERR, "MTU %u needs Rx scatter with %u byte Rx buffers",
+			    dev->data->mtu, rx_buf_len);
+		return -EINVAL;
+	}
+
 	/* Free memory if needed. */
 	if (dev->data->rx_queues[queue_id]) {
 		gve_rx_queue_release(dev, queue_id);
@@ -351,11 +374,7 @@ gve_rx_queue_setup(struct rte_eth_dev *dev, uint16_t queue_id,
 	rxq->hw = hw;
 	rxq->ntfy_addr = &hw->db_bar[rte_be_to_cpu_32(hw->irq_dbs[rxq->ntfy_id].id)];
 
-	mbuf_len =
-		rte_pktmbuf_data_room_size(rxq->mpool) - RTE_PKTMBUF_HEADROOM;
-	rxq->rx_buf_len =
-		RTE_MIN((uint16_t)GVE_RX_MAX_BUF_SIZE_GQI,
-			RTE_ALIGN_FLOOR(mbuf_len, GVE_RX_BUF_ALIGN_GQI));
+	rxq->rx_buf_len = rx_buf_len;
 
 	/* Allocate software ring */
 	rxq->sw_ring = rte_zmalloc_socket("gve rx sw ring", sizeof(struct rte_mbuf *) * nb_desc,
-- 
2.56.0.218.g1ec904b173-goog