[PATCH net-next 02/14] net/smc: Decouple sf and attached send_buf in smc_loopback

Alexandra Winter
2025-09-05T14:54:43Z

Before this patch there was the following assumption in
smc_loopback.c>smc_lo_move_data():
sf (signalling flag) == 0 : data is already in an attached target dmb
sf == 1 : data is not yet in the target dmb

This is true for the 2 callers in smc client
smcd_cdc_msg_send() : sf=1
smcd_tx_rdma_writes() : sf=0
but should not be a general assumption.

Add a bool to struct smc_buf_desc to indicate whether an SMC-D sndbuf_desc
is an attached buffer. Don't call move_data() for attached send_buffers,
because it is not necessary.

Move the data in smc_lo_move_data() if len != 0 and signal when requested.

Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Mahanta Jambigi <mjambigi@linux.ibm.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
---
net/smc/smc_core.h | 5 +++++
net/smc/smc_ism.c | 1 +
net/smc/smc_loopback.c | 9 +++------
net/smc/smc_tx.c | 3 +++
4 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
index 48a1b1dcb576..a5a78cbff341 100644
--- a/net/smc/smc_core.h
+++ b/net/smc/smc_core.h
@@ -13,6 +13,7 @@
#define _SMC_CORE_H

#include <linux/atomic.h>
+#include <linux/types.h>
#include <linux/smc.h>
#include <linux/pci.h>
#include <rdma/ib_verbs.h>
@@ -221,6 +222,10 @@ struct smc_buf_desc {
/* virtually contiguous */
};
struct { /* SMC-D */
+ /* SMC-D tx buffer */
+ bool is_attached;
+ /* no need for explicit writes */
+ /* SMC-D rx buffer: */
unsigned short sba_idx;
/* SBA index number */
u64 token;
diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
index fca01b95b65a..503a9f93b392 100644
--- a/net/smc/smc_ism.c
+++ b/net/smc/smc_ism.c
@@ -274,6 +274,7 @@ int smc_ism_attach_dmb(struct smcd_dev *dev, u64 token,
dmb_desc->cpu_addr = dmb.cpu_addr;
dmb_desc->dma_addr = dmb.dma_addr;
dmb_desc->len = dmb.dmb_len;
+ dmb_desc->is_attached = true;
}
return rc;
}
diff --git a/net/smc/smc_loopback.c b/net/smc/smc_loopback.c
index 0eb00bbefd17..1853c26fbbbb 100644
--- a/net/smc/smc_loopback.c
+++ b/net/smc/smc_loopback.c
@@ -224,12 +224,6 @@ static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
struct smc_lo_dev *ldev = smcd->priv;
struct smc_connection *conn;

- if (!sf)
- /* since sndbuf is merged with peer DMB, there is
- * no need to copy data from sndbuf to peer DMB.
- */
- return 0;
-
read_lock_bh(&ldev->dmb_ht_lock);
hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb_tok) {
if (tmp_node->token == dmb_tok) {
@@ -244,6 +238,9 @@ static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
memcpy((char *)rmb_node->cpu_addr + offset, data, size);
read_unlock_bh(&ldev->dmb_ht_lock);

+ if (!sf)
+ return 0;
+
conn = smcd->conn[rmb_node->sba_idx];
if (!conn || conn->killed)
return -EPIPE;
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 214ac3cbcf9a..3144b4b1fe29 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -426,6 +426,9 @@ static int smcd_tx_rdma_writes(struct smc_connection *conn, size_t len,
int srcchunk, dstchunk;
int rc;

+ if (conn->sndbuf_desc->is_attached)
+ return 0;
+
for (dstchunk = 0; dstchunk < 2; dstchunk++) {
for (srcchunk = 0; srcchunk < 2; srcchunk++) {
void *data = conn->sndbuf_desc->cpu_addr + src_off;
--
2.48.1