[PATCH v4 net-next 06/21] nvme-tcp: Add DDP offload control path

Boris Pismenny
2021-02-11T21:11:54Z

This commit introduces direct data placement offload to NVME
TCP. There is a context per queue, which is established after the
handshake using the tcp_ddp_sk_add/del NDOs.

Additionally, a resynchronization routine is used to assist
hardware recovery from TCP OOO, and continue the offload.
Resynchronization operates as follows:

1. TCP OOO causes the NIC HW to stop the offload

2. NIC HW identifies a PDU header at some TCP sequence number,
and asks NVMe-TCP to confirm it.
This request is delivered from the NIC driver to NVMe-TCP by first
finding the socket for the packet that triggered the request, and
then finding the nvme_tcp_queue that is used by this routine.
Finally, the request is recorded in the nvme_tcp_queue.

3. When NVMe-TCP observes the requested TCP sequence, it will compare
it with the PDU header TCP sequence, and report the result to the
NIC driver (tcp_ddp_resync), which will update the HW,
and resume offload when all is successful.

Furthermore, we let the offloading driver advertise what is the max hw
sectors/segments via tcp_ddp_limits.

A follow-up patch introduces the data-path changes required for this
offload.

Signed-off-by: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Ben Ben-Ishay <benishay@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Yoray Zack <yorayz@mellanox.com>
---
drivers/nvme/host/tcp.c | 177 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 175 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 881d28eb15e9..36de4391ba76 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -14,6 +14,7 @@
#include <linux/blk-mq.h>
#include <crypto/hash.h>
#include <net/busy_poll.h>
+#include <net/tcp_ddp.h>

#include "nvme.h"
#include "fabrics.h"
@@ -62,6 +63,7 @@ enum nvme_tcp_queue_flags {
NVME_TCP_Q_ALLOCATED = 0,
NVME_TCP_Q_LIVE = 1,
NVME_TCP_Q_POLLING = 2,
+ NVME_TCP_Q_OFF_DDP = 3,
};

enum nvme_tcp_recv_state {
@@ -111,6 +113,8 @@ struct nvme_tcp_queue {
void (*state_change)(struct sock *);
void (*data_ready)(struct sock *);
void (*write_space)(struct sock *);
+
+ atomic64_t resync_req;
};

struct nvme_tcp_ctrl {
@@ -129,6 +133,8 @@ struct nvme_tcp_ctrl {
struct delayed_work connect_work;
struct nvme_tcp_request async_req;
u32 io_queues[HCTX_MAX_TYPES];
+
+ struct net_device *offloading_netdev;
};

static LIST_HEAD(nvme_tcp_ctrl_list);
@@ -223,6 +229,164 @@ static inline size_t nvme_tcp_pdu_last_send(struct nvme_tcp_request *req,
return nvme_tcp_pdu_data_left(req) <= len;
}

+#ifdef CONFIG_TCP_DDP
+
+static bool nvme_tcp_resync_request(struct sock *sk, u32 seq, u32 flags);
+static const struct tcp_ddp_ulp_ops nvme_tcp_ddp_ulp_ops = {
+ .resync_request = nvme_tcp_resync_request,
+};
+
+static int nvme_tcp_offload_socket(struct nvme_tcp_queue *queue)
+{
+ struct net_device *netdev = queue->ctrl->offloading_netdev;
+ struct nvme_tcp_ddp_config config = {};
+ int ret;
+
+ if (!(netdev->features & NETIF_F_HW_TCP_DDP))
+ return -EOPNOTSUPP;
+
+ config.cfg.type = TCP_DDP_NVME;
+ config.pfv = NVME_TCP_PFV_1_0;
+ config.cpda = 0;
+ config.dgst = queue->hdr_digest ?
+ NVME_TCP_HDR_DIGEST_ENABLE : 0;
+ config.dgst |= queue->data_digest ?
+ NVME_TCP_DATA_DIGEST_ENABLE : 0;
+ config.queue_size = queue->queue_size;
+ config.queue_id = nvme_tcp_queue_id(queue);
+ config.io_cpu = queue->io_cpu;
+
+ dev_hold(netdev); /* put by unoffload_socket */
+ ret = netdev->tcp_ddp_ops->tcp_ddp_sk_add(netdev,
+ queue->sock->sk,
+ &config.cfg);
+ if (ret) {
+ dev_put(netdev);
+ return ret;
+ }
+
+ inet_csk(queue->sock->sk)->icsk_ulp_ddp_ops = &nvme_tcp_ddp_ulp_ops;
+ if (netdev->features & NETIF_F_HW_TCP_DDP)
+ set_bit(NVME_TCP_Q_OFF_DDP, &queue->flags);
+
+ return ret;
+}
+
+static void nvme_tcp_unoffload_socket(struct nvme_tcp_queue *queue)
+{
+ struct net_device *netdev = queue->ctrl->offloading_netdev;
+
+ if (!netdev) {
+ dev_info_ratelimited(queue->ctrl->ctrl.device, "netdev not found\n");
+ return;
+ }
+
+ netdev->tcp_ddp_ops->tcp_ddp_sk_del(netdev, queue->sock->sk);
+
+ inet_csk(queue->sock->sk)->icsk_ulp_ddp_ops = NULL;
+ dev_put(netdev); /* held by offload_socket */
+}
+
+static int nvme_tcp_offload_limits(struct nvme_tcp_queue *queue)
+{
+ struct net_device *netdev = get_netdev_for_sock(queue->sock->sk, true);
+ struct tcp_ddp_limits limits;
+ int ret = 0;
+
+ if (!netdev) {
+ dev_info_ratelimited(queue->ctrl->ctrl.device, "netdev not found\n");
+ queue->ctrl->offloading_netdev = NULL;
+ return -ENODEV;
+ }
+
+ if (netdev->features & NETIF_F_HW_TCP_DDP &&
+ netdev->tcp_ddp_ops &&
+ netdev->tcp_ddp_ops->tcp_ddp_limits)
+ ret = netdev->tcp_ddp_ops->tcp_ddp_limits(netdev, &limits);
+ else
+ ret = -EOPNOTSUPP;
+
+ if (!ret) {
+ queue->ctrl->offloading_netdev = netdev;
+ dev_dbg_ratelimited(queue->ctrl->ctrl.device,
+ "netdev %s offload limits: max_ddp_sgl_len %d\n",
+ netdev->name, limits.max_ddp_sgl_len);
+ queue->ctrl->ctrl.max_segments = limits.max_ddp_sgl_len;
+ queue->ctrl->ctrl.max_hw_sectors =
+ limits.max_ddp_sgl_len << (ilog2(SZ_4K) - 9);
+ } else {
+ queue->ctrl->offloading_netdev = NULL;
+ }
+
+ /* release the device as no offload context is established yet. */
+ dev_put(netdev);
+
+ return ret;
+}
+
+static void nvme_tcp_resync_response(struct nvme_tcp_queue *queue,
+ struct sk_buff *skb, unsigned int offset)
+{
+ u64 pdu_seq = TCP_SKB_CB(skb)->seq + offset - queue->pdu_offset;
+ struct net_device *netdev = queue->ctrl->offloading_netdev;
+ u64 resync_val;
+ u32 resync_seq;
+
+ resync_val = atomic64_read(&queue->resync_req);
+ /* Lower 32 bit flags. Check validity of the request */
+ if ((resync_val & TCP_DDP_RESYNC_REQ) == 0)
+ return;
+
+ /* Obtain and check requested sequence number: is this PDU header before the request? */
+ resync_seq = resync_val >> 32;
+ if (before(pdu_seq, resync_seq))
+ return;
+
+ if (unlikely(!netdev)) {
+ pr_info_ratelimited("%s: netdev not found\n", __func__);
+ return;
+ }
+
+ /**
+ * The atomic operation gurarantees that we don't miss any NIC driver
+ * resync requests submitted after the above checks.
+ */
+ if (atomic64_cmpxchg(&queue->resync_req, resync_val,
+ resync_val & ~TCP_DDP_RESYNC_REQ))
+ netdev->tcp_ddp_ops->tcp_ddp_resync(netdev, queue->sock->sk, pdu_seq);
+}
+
+static bool nvme_tcp_resync_request(struct sock *sk, u32 seq, u32 flags)
+{
+ struct nvme_tcp_queue *queue = sk->sk_user_data;
+
+ atomic64_set(&queue->resync_req,
+ (((uint64_t)seq << 32) | flags));
+
+ return true;
+}
+
+#else
+
+static int nvme_tcp_offload_socket(struct nvme_tcp_queue *queue)
+{
+ return -EINVAL;
+}
+
+static void nvme_tcp_unoffload_socket(struct nvme_tcp_queue *queue)
+{}
+
+static int nvme_tcp_offload_limits(struct nvme_tcp_queue *queue)
+{
+ return -EINVAL;
+}
+
+static void nvme_tcp_resync_response(struct nvme_tcp_queue *queue,
+ struct sk_buff *skb, unsigned int offset)
+{}
+
+#endif
+
static void nvme_tcp_init_iter(struct nvme_tcp_request *req,
unsigned int dir)
{
@@ -638,6 +802,9 @@ static int nvme_tcp_recv_pdu(struct nvme_tcp_queue *queue, struct sk_buff *skb,
size_t rcv_len = min_t(size_t, *len, queue->pdu_remaining);
int ret;

+ if (test_bit(NVME_TCP_Q_OFF_DDP, &queue->flags))
+ nvme_tcp_resync_response(queue, skb, *offset);
+
ret = skb_copy_bits(skb, *offset,
&pdu[queue->pdu_offset], rcv_len);
if (unlikely(ret))
@@ -1532,6 +1699,9 @@ static void __nvme_tcp_stop_queue(struct nvme_tcp_queue *queue)
kernel_sock_shutdown(queue->sock, SHUT_RDWR);
nvme_tcp_restore_sock_calls(queue);
cancel_work_sync(&queue->io_work);
+
+ if (test_bit(NVME_TCP_Q_OFF_DDP, &queue->flags))
+ nvme_tcp_unoffload_socket(queue);
}

static void nvme_tcp_stop_queue(struct nvme_ctrl *nctrl, int qid)
@@ -1550,10 +1720,13 @@ static int nvme_tcp_start_queue(struct nvme_ctrl *nctrl, int idx)
struct nvme_tcp_ctrl *ctrl = to_tcp_ctrl(nctrl);
int ret;

- if (idx)
+ if (idx) {
ret = nvmf_connect_io_queue(nctrl, idx, false);
- else
+ nvme_tcp_offload_socket(&ctrl->queues[idx]);
+ } else {
ret = nvmf_connect_admin_queue(nctrl);
+ nvme_tcp_offload_limits(&ctrl->queues[idx]);
+ }

if (!ret) {
set_bit(NVME_TCP_Q_LIVE, &ctrl->queues[idx].flags);