net/smc/smc_core.c

/*
 *  Shared Memory Communications over RDMA (SMC-R) and RoCE
 *
 *  Basic Transport Functions exploiting Infiniband API
 *
 *  Copyright IBM Corp. 2016
 *
 *  Author(s):  Ursula Braun <ubraun@linux.vnet.ibm.com>
 */

#include <linux/socket.h>
#include <linux/if_vlan.h>
#include <linux/random.h>
#include <linux/workqueue.h>
#include <net/tcp.h>
#include <net/sock.h>
#include <rdma/ib_verbs.h>

#include "smc.h"
#include "smc_clc.h"
#include "smc_core.h"
#include "smc_ib.h"
#include "smc_wr.h"
#include "smc_llc.h"
#include "smc_cdc.h"
#include "smc_close.h"

#define SMC_LGR_NUM_INCR	256
#define SMC_LGR_FREE_DELAY	(600 * HZ)

static u32 smc_lgr_num;			/* unique link group number */

/* Register connection's alert token in our lookup structure.
 * To use rbtrees we have to implement our own insert core.
 * Requires @conns_lock
 * @smc		connection to register
 * Returns 0 on success, != otherwise.
 */
static void smc_lgr_add_alert_token(struct smc_connection *conn)
{
	struct rb_node **link, *parent = NULL;
	u32 token = conn->alert_token_local;

	link = &conn->lgr->conns_all.rb_node;
	while (*link) {
		struct smc_connection *cur = rb_entry(*link,
					struct smc_connection, alert_node);

		parent = *link;
		if (cur->alert_token_local > token)
			link = &parent->rb_left;
		else
			link = &parent->rb_right;
	}
	/* Put the new node there */
	rb_link_node(&conn->alert_node, parent, link);
	rb_insert_color(&conn->alert_node, &conn->lgr->conns_all);
}

/* Register connection in link group by assigning an alert token
 * registered in a search tree.
 * Requires @conns_lock
 * Note that '0' is a reserved value and not assigned.
 */
static void smc_lgr_register_conn(struct smc_connection *conn)
{
	struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
	static atomic_t nexttoken = ATOMIC_INIT(0);

	/* find a new alert_token_local value not yet used by some connection
	 * in this link group
	 */
	sock_hold(&smc->sk); /* sock_put in smc_lgr_unregister_conn() */
	while (!conn->alert_token_local) {
		conn->alert_token_local = atomic_inc_return(&nexttoken);
		if (smc_lgr_find_conn(conn->alert_token_local, conn->lgr))
			conn->alert_token_local = 0;
	}
	smc_lgr_add_alert_token(conn);
	conn->lgr->conns_num++;
}

/* Unregister connection and reset the alert token of the given connection<
 */
static void __smc_lgr_unregister_conn(struct smc_connection *conn)
{
	struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
	struct smc_link_group *lgr = conn->lgr;

	rb_erase(&conn->alert_node, &lgr->conns_all);
	lgr->conns_num--;
	conn->alert_token_local = 0;
	conn->lgr = NULL;
	sock_put(&smc->sk); /* sock_hold in smc_lgr_register_conn() */
}

/* Unregister connection and trigger lgr freeing if applicable
 */
static void smc_lgr_unregister_conn(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;
	int reduced = 0;

	write_lock_bh(&lgr->conns_lock);
	if (conn->alert_token_local) {
		reduced = 1;
		__smc_lgr_unregister_conn(conn);
	}
	write_unlock_bh(&lgr->conns_lock);
	if (reduced && !lgr->conns_num)
		schedule_delayed_work(&lgr->free_work, SMC_LGR_FREE_DELAY);
}

static void smc_lgr_free_work(struct work_struct *work)
{
	struct smc_link_group *lgr = container_of(to_delayed_work(work),
						  struct smc_link_group,
						  free_work);
	bool conns;

	spin_lock_bh(&smc_lgr_list.lock);
	read_lock_bh(&lgr->conns_lock);
	conns = RB_EMPTY_ROOT(&lgr->conns_all);
	read_unlock_bh(&lgr->conns_lock);
	if (!conns) { /* number of lgr connections is no longer zero */
		spin_unlock_bh(&smc_lgr_list.lock);
		return;
	}
	list_del_init(&lgr->list); /* remove from smc_lgr_list */
	spin_unlock_bh(&smc_lgr_list.lock);
	smc_lgr_free(lgr);
}

/* create a new SMC link group */
static int smc_lgr_create(struct smc_sock *smc, __be32 peer_in_addr,
			  struct smc_ib_device *smcibdev, u8 ibport,
			  char *peer_systemid, unsigned short vlan_id)
{
	struct smc_link_group *lgr;
	struct smc_link *lnk;
	u8 rndvec[3];
	int rc = 0;
	int i;

	lgr = kzalloc(sizeof(*lgr), GFP_KERNEL);
	if (!lgr) {
		rc = -ENOMEM;
		goto out;
	}
	lgr->role = smc->listen_smc ? SMC_SERV : SMC_CLNT;
	lgr->sync_err = false;
	lgr->daddr = peer_in_addr;
	memcpy(lgr->peer_systemid, peer_systemid, SMC_SYSTEMID_LEN);
	lgr->vlan_id = vlan_id;
	rwlock_init(&lgr->sndbufs_lock);
	rwlock_init(&lgr->rmbs_lock);
	for (i = 0; i < SMC_RMBE_SIZES; i++) {
		INIT_LIST_HEAD(&lgr->sndbufs[i]);
		INIT_LIST_HEAD(&lgr->rmbs[i]);
	}
	smc_lgr_num += SMC_LGR_NUM_INCR;
	memcpy(&lgr->id, (u8 *)&smc_lgr_num, SMC_LGR_ID_SIZE);
	INIT_DELAYED_WORK(&lgr->free_work, smc_lgr_free_work);
	lgr->conns_all = RB_ROOT;

	lnk = &lgr->lnk[SMC_SINGLE_LINK];
	/* initialize link */
	lnk->smcibdev = smcibdev;
	lnk->ibport = ibport;
	lnk->path_mtu = smcibdev->pattr[ibport - 1].active_mtu;
	if (!smcibdev->initialized)
		smc_ib_setup_per_ibdev(smcibdev);
	get_random_bytes(rndvec, sizeof(rndvec));
	lnk->psn_initial = rndvec[0] + (rndvec[1] << 8) + (rndvec[2] << 16);
	rc = smc_wr_alloc_link_mem(lnk);
	if (rc)
		goto free_lgr;
	rc = smc_ib_create_protection_domain(lnk);
	if (rc)
		goto free_link_mem;
	rc = smc_ib_create_queue_pair(lnk);
	if (rc)
		goto dealloc_pd;
	rc = smc_wr_create_link(lnk);
	if (rc)
		goto destroy_qp;
	init_completion(&lnk->llc_confirm);
	init_completion(&lnk->llc_confirm_resp);

	smc->conn.lgr = lgr;
	rwlock_init(&lgr->conns_lock);
	spin_lock_bh(&smc_lgr_list.lock);
	list_add(&lgr->list, &smc_lgr_list.list);
	spin_unlock_bh(&smc_lgr_list.lock);
	return 0;

destroy_qp:
	smc_ib_destroy_queue_pair(lnk);
dealloc_pd:
	smc_ib_dealloc_protection_domain(lnk);
free_link_mem:
	smc_wr_free_link_mem(lnk);
free_lgr:
	kfree(lgr);
out:
	return rc;
}

static void smc_buf_unuse(struct smc_connection *conn)
{
	if (conn->sndbuf_desc) {
		conn->sndbuf_desc->used = 0;
		conn->sndbuf_size = 0;
	}
	if (conn->rmb_desc) {
		conn->rmb_desc->reused = true;
		conn->rmb_desc->used = 0;
		conn->rmbe_size = 0;
	}
}

/* remove a finished connection from its link group */
void smc_conn_free(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;

	if (!lgr)
		return;
	smc_cdc_tx_dismiss_slots(conn);
	smc_lgr_unregister_conn(conn);
	smc_buf_unuse(conn);
}

static void smc_link_clear(struct smc_link *lnk)
{
	lnk->peer_qpn = 0;
	smc_ib_modify_qp_reset(lnk);
	smc_wr_free_link(lnk);
	smc_ib_destroy_queue_pair(lnk);
	smc_ib_dealloc_protection_domain(lnk);
	smc_wr_free_link_mem(lnk);
}

static void smc_buf_free(struct smc_buf_desc *buf_desc, struct smc_link *lnk,
			 bool is_rmb)
{
	if (is_rmb) {
		if (buf_desc->mr_rx[SMC_SINGLE_LINK])
			smc_ib_put_memory_region(
					buf_desc->mr_rx[SMC_SINGLE_LINK]);
		smc_ib_buf_unmap_sg(lnk->smcibdev, buf_desc,
				    DMA_FROM_DEVICE);
	} else {
		smc_ib_buf_unmap_sg(lnk->smcibdev, buf_desc,
				    DMA_TO_DEVICE);
	}
	sg_free_table(&buf_desc->sgt[SMC_SINGLE_LINK]);
	if (buf_desc->cpu_addr)
		free_pages((unsigned long)buf_desc->cpu_addr, buf_desc->order);
	kfree(buf_desc);
}

static void __smc_lgr_free_bufs(struct smc_link_group *lgr, bool is_rmb)
{
	struct smc_link *lnk = &lgr->lnk[SMC_SINGLE_LINK];
	struct smc_buf_desc *buf_desc, *bf_desc;
	struct list_head *buf_list;
	int i;

	for (i = 0; i < SMC_RMBE_SIZES; i++) {
		if (is_rmb)
			buf_list = &lgr->rmbs[i];
		else
			buf_list = &lgr->sndbufs[i];
		list_for_each_entry_safe(buf_desc, bf_desc, buf_list,
					 list) {
			list_del(&buf_desc->list);
			smc_buf_free(buf_desc, lnk, is_rmb);
		}
	}
}

static void smc_lgr_free_bufs(struct smc_link_group *lgr)
{
	/* free send buffers */
	__smc_lgr_free_bufs(lgr, false);
	/* free rmbs */
	__smc_lgr_free_bufs(lgr, true);
}

/* remove a link group */
void smc_lgr_free(struct smc_link_group *lgr)
{
	smc_lgr_free_bufs(lgr);
	smc_link_clear(&lgr->lnk[SMC_SINGLE_LINK]);
	kfree(lgr);
}

/* terminate linkgroup abnormally */
void smc_lgr_terminate(struct smc_link_group *lgr)
{
	struct smc_connection *conn;
	struct smc_sock *smc;
	struct rb_node *node;

	spin_lock_bh(&smc_lgr_list.lock);
	if (list_empty(&lgr->list)) {
		/* termination already triggered */
		spin_unlock_bh(&smc_lgr_list.lock);
		return;
	}
	/* do not use this link group for new connections */
	list_del_init(&lgr->list);
	spin_unlock_bh(&smc_lgr_list.lock);

	write_lock_bh(&lgr->conns_lock);
	node = rb_first(&lgr->conns_all);
	while (node) {
		conn = rb_entry(node, struct smc_connection, alert_node);
		smc = container_of(conn, struct smc_sock, conn);
		sock_hold(&smc->sk);
		__smc_lgr_unregister_conn(conn);
		schedule_work(&conn->close_work);
		sock_put(&smc->sk);
		node = rb_first(&lgr->conns_all);
	}
	write_unlock_bh(&lgr->conns_lock);
}

/* Determine vlan of internal TCP socket.
 * @vlan_id: address to store the determined vlan id into
 */
static int smc_vlan_by_tcpsk(struct socket *clcsock, unsigned short *vlan_id)
{
	struct dst_entry *dst = sk_dst_get(clcsock->sk);
	int rc = 0;

	*vlan_id = 0;
	if (!dst) {
		rc = -ENOTCONN;
		goto out;
	}
	if (!dst->dev) {
		rc = -ENODEV;
		goto out_rel;
	}

	if (is_vlan_dev(dst->dev))
		*vlan_id = vlan_dev_vlan_id(dst->dev);

out_rel:
	dst_release(dst);
out:
	return rc;
}

/* determine the link gid matching the vlan id of the link group */
static int smc_link_determine_gid(struct smc_link_group *lgr)
{
	struct smc_link *lnk = &lgr->lnk[SMC_SINGLE_LINK];
	struct ib_gid_attr gattr;
	union ib_gid gid;
	int i;

	if (!lgr->vlan_id) {
		lnk->gid = lnk->smcibdev->gid[lnk->ibport - 1];
		return 0;
	}

	for (i = 0; i < lnk->smcibdev->pattr[lnk->ibport - 1].gid_tbl_len;
	     i++) {
		if (ib_query_gid(lnk->smcibdev->ibdev, lnk->ibport, i, &gid,
				 &gattr))
			continue;
		if (gattr.ndev &&
		    (vlan_dev_vlan_id(gattr.ndev) == lgr->vlan_id)) {
			lnk->gid = gid;
			return 0;
		}
	}
	return -ENODEV;
}

/* create a new SMC connection (and a new link group if necessary) */
int smc_conn_create(struct smc_sock *smc, __be32 peer_in_addr,
		    struct smc_ib_device *smcibdev, u8 ibport,
		    struct smc_clc_msg_local *lcl, int srv_first_contact)
{
	struct smc_connection *conn = &smc->conn;
	struct smc_link_group *lgr;
	unsigned short vlan_id;
	enum smc_lgr_role role;
	int local_contact = SMC_FIRST_CONTACT;
	int rc = 0;

	role = smc->listen_smc ? SMC_SERV : SMC_CLNT;
	rc = smc_vlan_by_tcpsk(smc->clcsock, &vlan_id);
	if (rc)
		return rc;

	if ((role == SMC_CLNT) && srv_first_contact)
		/* create new link group as well */
		goto create;

	/* determine if an existing link group can be reused */
	spin_lock_bh(&smc_lgr_list.lock);
	list_for_each_entry(lgr, &smc_lgr_list.list, list) {
		write_lock_bh(&lgr->conns_lock);
		if (!memcmp(lgr->peer_systemid, lcl->id_for_peer,
			    SMC_SYSTEMID_LEN) &&
		    !memcmp(lgr->lnk[SMC_SINGLE_LINK].peer_gid, &lcl->gid,
			    SMC_GID_SIZE) &&
		    !memcmp(lgr->lnk[SMC_SINGLE_LINK].peer_mac, lcl->mac,
			    sizeof(lcl->mac)) &&
		    !lgr->sync_err &&
		    (lgr->role == role) &&
		    (lgr->vlan_id == vlan_id) &&
		    ((role == SMC_CLNT) ||
		     (lgr->conns_num < SMC_RMBS_PER_LGR_MAX))) {
			/* link group found */
			local_contact = SMC_REUSE_CONTACT;
			conn->lgr = lgr;
			smc_lgr_register_conn(conn); /* add smc conn to lgr */
			write_unlock_bh(&lgr->conns_lock);
			break;
		}
		write_unlock_bh(&lgr->conns_lock);
	}
	spin_unlock_bh(&smc_lgr_list.lock);

	if (role == SMC_CLNT && !srv_first_contact &&
	    (local_contact == SMC_FIRST_CONTACT)) {
		/* Server reuses a link group, but Client wants to start
		 * a new one
		 * send out_of_sync decline, reason synchr. error
		 */
		return -ENOLINK;
	}

create:
	if (local_contact == SMC_FIRST_CONTACT) {
		rc = smc_lgr_create(smc, peer_in_addr, smcibdev, ibport,
				    lcl->id_for_peer, vlan_id);
		if (rc)
			goto out;
		smc_lgr_register_conn(conn); /* add smc conn to lgr */
		rc = smc_link_determine_gid(conn->lgr);
	}
	conn->local_tx_ctrl.common.type = SMC_CDC_MSG_TYPE;
	conn->local_tx_ctrl.len = sizeof(struct smc_cdc_msg);
#ifndef KERNEL_HAS_ATOMIC64
	spin_lock_init(&conn->acurs_lock);
#endif

out:
	return rc ? rc : local_contact;
}

/* try to reuse a sndbuf or rmb description slot for a certain
 * buffer size; if not available, return NULL
 */
static inline
struct smc_buf_desc *smc_buf_get_slot(struct smc_link_group *lgr,
				      int compressed_bufsize,
				      rwlock_t *lock,
				      struct list_head *buf_list)
{
	struct smc_buf_desc *buf_slot;

	read_lock_bh(lock);
	list_for_each_entry(buf_slot, buf_list, list) {
		if (cmpxchg(&buf_slot->used, 0, 1) == 0) {
			read_unlock_bh(lock);
			return buf_slot;
		}
	}
	read_unlock_bh(lock);
	return NULL;
}

/* one of the conditions for announcing a receiver's current window size is
 * that it "results in a minimum increase in the window size of 10% of the
 * receive buffer space" [RFC7609]
 */
static inline int smc_rmb_wnd_update_limit(int rmbe_size)
{
	return min_t(int, rmbe_size / 10, SOCK_MIN_SNDBUF / 2);
}

static struct smc_buf_desc *smc_new_buf_create(struct smc_link_group *lgr,
					       bool is_rmb, int bufsize)
{
	struct smc_buf_desc *buf_desc;
	struct smc_link *lnk;
	int rc;

	/* try to alloc a new buffer */
	buf_desc = kzalloc(sizeof(*buf_desc), GFP_KERNEL);
	if (!buf_desc)
		return ERR_PTR(-ENOMEM);

	buf_desc->cpu_addr =
		(void *)__get_free_pages(GFP_KERNEL | __GFP_NOWARN |
					 __GFP_NOMEMALLOC |
					 __GFP_NORETRY | __GFP_ZERO,
					 get_order(bufsize));
	if (!buf_desc->cpu_addr) {
		kfree(buf_desc);
		return ERR_PTR(-EAGAIN);
	}
	buf_desc->order = get_order(bufsize);

	/* build the sg table from the pages */
	lnk = &lgr->lnk[SMC_SINGLE_LINK];
	rc = sg_alloc_table(&buf_desc->sgt[SMC_SINGLE_LINK], 1,
			    GFP_KERNEL);
	if (rc) {
		smc_buf_free(buf_desc, lnk, is_rmb);
		return ERR_PTR(rc);
	}
	sg_set_buf(buf_desc->sgt[SMC_SINGLE_LINK].sgl,
		   buf_desc->cpu_addr, bufsize);

	/* map sg table to DMA address */
	rc = smc_ib_buf_map_sg(lnk->smcibdev, buf_desc,
			       is_rmb ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
	/* SMC protocol depends on mapping to one DMA address only */
	if (rc != 1)  {
		smc_buf_free(buf_desc, lnk, is_rmb);
		return ERR_PTR(-EAGAIN);
	}

	/* create a new memory region for the RMB */
	if (is_rmb) {
		rc = smc_ib_get_memory_region(lnk->roce_pd,
					      IB_ACCESS_REMOTE_WRITE |
					      IB_ACCESS_LOCAL_WRITE,
					      buf_desc);
		if (rc) {
			smc_buf_free(buf_desc, lnk, is_rmb);
			return ERR_PTR(rc);
		}
	}

	return buf_desc;
}

static int __smc_buf_create(struct smc_sock *smc, bool is_rmb)
{
	struct smc_connection *conn = &smc->conn;
	struct smc_link_group *lgr = conn->lgr;
	struct smc_buf_desc *buf_desc = NULL;
	struct list_head *buf_list;
	int bufsize, bufsize_short;
	int sk_buf_size;
	rwlock_t *lock;

	if (is_rmb)
		/* use socket recv buffer size (w/o overhead) as start value */
		sk_buf_size = smc->sk.sk_rcvbuf / 2;
	else
		/* use socket send buffer size (w/o overhead) as start value */
		sk_buf_size = smc->sk.sk_sndbuf / 2;

	for (bufsize_short = smc_compress_bufsize(smc->sk.sk_sndbuf / 2);
	     bufsize_short >= 0; bufsize_short--) {

		if (is_rmb) {
			lock = &lgr->rmbs_lock;
			buf_list = &lgr->rmbs[bufsize_short];
		} else {
			lock = &lgr->sndbufs_lock;
			buf_list = &lgr->sndbufs[bufsize_short];
		}
		bufsize = smc_uncompress_bufsize(bufsize_short);
		if ((1 << get_order(bufsize)) > SG_MAX_SINGLE_ALLOC)
			continue;

		/* check for reusable slot in the link group */
		buf_desc = smc_buf_get_slot(lgr, bufsize_short, lock, buf_list);
		if (buf_desc) {
			memset(buf_desc->cpu_addr, 0, bufsize);
			break; /* found reusable slot */
		}

		buf_desc = smc_new_buf_create(lgr, is_rmb, bufsize);
		if (PTR_ERR(buf_desc) == -ENOMEM)
			break;
		if (IS_ERR(buf_desc))
			continue;

		buf_desc->used = 1;
		write_lock_bh(lock);
		list_add(&buf_desc->list, buf_list);
		write_unlock_bh(lock);
		break; /* found */
	}

	if (IS_ERR(buf_desc))
		return -ENOMEM;

	if (is_rmb) {
		conn->rmb_desc = buf_desc;
		conn->rmbe_size = bufsize;
		conn->rmbe_size_short = bufsize_short;
		smc->sk.sk_rcvbuf = bufsize * 2;
		atomic_set(&conn->bytes_to_rcv, 0);
		conn->rmbe_update_limit = smc_rmb_wnd_update_limit(bufsize);
	} else {
		conn->sndbuf_desc = buf_desc;
		conn->sndbuf_size = bufsize;
		smc->sk.sk_sndbuf = bufsize * 2;
		atomic_set(&conn->sndbuf_space, bufsize);
	}
	return 0;
}

void smc_sndbuf_sync_sg_for_cpu(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;

	smc_ib_sync_sg_for_cpu(lgr->lnk[SMC_SINGLE_LINK].smcibdev,
			       conn->sndbuf_desc, DMA_TO_DEVICE);
}

void smc_sndbuf_sync_sg_for_device(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;

	smc_ib_sync_sg_for_device(lgr->lnk[SMC_SINGLE_LINK].smcibdev,
				  conn->sndbuf_desc, DMA_TO_DEVICE);
}

void smc_rmb_sync_sg_for_cpu(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;

	smc_ib_sync_sg_for_cpu(lgr->lnk[SMC_SINGLE_LINK].smcibdev,
			       conn->rmb_desc, DMA_FROM_DEVICE);
}

void smc_rmb_sync_sg_for_device(struct smc_connection *conn)
{
	struct smc_link_group *lgr = conn->lgr;

	smc_ib_sync_sg_for_device(lgr->lnk[SMC_SINGLE_LINK].smcibdev,
				  conn->rmb_desc, DMA_FROM_DEVICE);
}

/* create the send and receive buffer for an SMC socket;
 * receive buffers are called RMBs;
 * (even though the SMC protocol allows more than one RMB-element per RMB,
 * the Linux implementation uses just one RMB-element per RMB, i.e. uses an
 * extra RMB for every connection in a link group
 */
int smc_buf_create(struct smc_sock *smc)
{
	int rc;

	/* create send buffer */
	rc = __smc_buf_create(smc, false);
	if (rc)
		return rc;
	/* create rmb */
	rc = __smc_buf_create(smc, true);
	if (rc)
		smc_buf_free(smc->conn.sndbuf_desc,
			     &smc->conn.lgr->lnk[SMC_SINGLE_LINK], false);
	return rc;
}

static inline int smc_rmb_reserve_rtoken_idx(struct smc_link_group *lgr)
{
	int i;

	for_each_clear_bit(i, lgr->rtokens_used_mask, SMC_RMBS_PER_LGR_MAX) {
		if (!test_and_set_bit(i, lgr->rtokens_used_mask))
			return i;
	}
	return -ENOSPC;
}

/* save rkey and dma_addr received from peer during clc handshake */
int smc_rmb_rtoken_handling(struct smc_connection *conn,
			    struct smc_clc_msg_accept_confirm *clc)
{
	u64 dma_addr = be64_to_cpu(clc->rmb_dma_addr);
	struct smc_link_group *lgr = conn->lgr;
	u32 rkey = ntohl(clc->rmb_rkey);
	int i;

	for (i = 0; i < SMC_RMBS_PER_LGR_MAX; i++) {
		if ((lgr->rtokens[i][SMC_SINGLE_LINK].rkey == rkey) &&
		    (lgr->rtokens[i][SMC_SINGLE_LINK].dma_addr == dma_addr) &&
		    test_bit(i, lgr->rtokens_used_mask)) {
			conn->rtoken_idx = i;
			return 0;
		}
	}
	conn->rtoken_idx = smc_rmb_reserve_rtoken_idx(lgr);
	if (conn->rtoken_idx < 0)
		return conn->rtoken_idx;
	lgr->rtokens[conn->rtoken_idx][SMC_SINGLE_LINK].rkey = rkey;
	lgr->rtokens[conn->rtoken_idx][SMC_SINGLE_LINK].dma_addr = dma_addr;
	return 0;
}