RDMA/efa: Add initialization of AH cache rhashtable

New EFA devices don't support the creation of multiple address handles
to the same remote on the same PD.
To overcome this limitation, introduce an AH cache rhashtable which will
store the user refcounts of the same AH creation on the same PD and will
allow the driver to manage AH reuse. The hashtable key is the
combination of PD and GID. Add initialization and teardown logic for the
rhashtable.

Each entry holds a refcount to manage the entry lifetime in the
hashtable and a user count that indicates how many users are using the
address handle.

Reviewed-by: Firas Jahjah <firasj@amazon.com>
Reviewed-by: Michael Margolin <mrgolin@amazon.com>
Signed-off-by: Yonatan Nachum <ynachum@amazon.com>
Link: https://patch.msgid.link/20260706170008.1039417-2-ynachum@amazon.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/hw/efa/Makefile

@@ -1,9 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
-# Copyright 2018-2019 Amazon.com, Inc. or its affiliates. All rights reserved.
+# Copyright 2018-2026 Amazon.com, Inc. or its affiliates. All rights reserved.
 #
 # Makefile for Amazon Elastic Fabric Adapter (EFA) device driver.
 #
 
 obj-$(CONFIG_INFINIBAND_EFA) += efa.o
 
-efa-y := efa_com_cmd.o efa_com.o efa_main.o efa_verbs.o
+efa-y := efa_com_cmd.o efa_ah_cache.o efa_com.o efa_main.o efa_verbs.o

drivers/infiniband/hw/efa/efa_ah_cache.c

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/*
+ * Copyright 2026 Amazon.com, Inc. or its affiliates. All rights reserved.
+ */
+
+#include <linux/slab.h>
+
+#include "efa_ah_cache.h"
+
+static const struct rhashtable_params ah_cache_params = {
+	.key_len = sizeof(struct efa_ah_cache_key),
+	.key_offset = offsetof(struct efa_ah_cache_entry, key),
+	.head_offset = offsetof(struct efa_ah_cache_entry, linkage),
+};
+
+int efa_ah_cache_init(struct efa_ah_cache *ah_cache)
+{
+	int err;
+
+	mutex_init(&ah_cache->lock);
+	err = rhashtable_init(&ah_cache->hashtable, &ah_cache_params);
+	if (err)
+		mutex_destroy(&ah_cache->lock);
+
+	return err;
+}
+
+static void efa_ah_cache_entry_free(void *ptr, void *arg)
+{
+	struct efa_ah_cache_entry *entry = ptr;
+
+	WARN_ON(entry->usecnt);
+	mutex_destroy(&entry->lock);
+	kfree(entry);
+}
+
+void efa_ah_cache_destroy(struct efa_ah_cache *ah_cache)
+{
+	rhashtable_free_and_destroy(&ah_cache->hashtable, efa_ah_cache_entry_free, NULL);
+	mutex_destroy(&ah_cache->lock);
+}

drivers/infiniband/hw/efa/efa_ah_cache.h

@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause */
+/*
+ * Copyright 2026 Amazon.com, Inc. or its affiliates. All rights reserved.
+ */
+
+#ifndef _EFA_AH_CACHE_H_
+#define _EFA_AH_CACHE_H_
+
+#include <linux/refcount.h>
+#include <linux/rhashtable.h>
+
+#define EFA_AH_GID_SIZE 16
+
+struct efa_ah_cache_key {
+	u8 gid[EFA_AH_GID_SIZE];
+	u16 pd;
+};
+
+struct efa_ah_cache_entry {
+	struct efa_ah_cache_key key;
+	u16 ah;
+	unsigned int usecnt;
+	refcount_t refcount;
+	struct rhash_head linkage;
+	struct mutex lock; /* Serializes device commands per cache entry */
+};
+
+struct efa_ah_cache {
+	struct rhashtable hashtable;
+	struct mutex lock; /* Protects AH cache hashtable */
+};
+
+int efa_ah_cache_init(struct efa_ah_cache *ah_cache);
+void efa_ah_cache_destroy(struct efa_ah_cache *ah_cache);
+
+#endif /* _EFA_AH_CACHE_H_ */

drivers/infiniband/hw/efa/efa_com.c

@@ -724,6 +724,8 @@ void efa_com_admin_destroy(struct efa_com_dev *edev)
 
 	size = aenq->depth * sizeof(*aenq->entries);
 	dma_free_coherent(edev->dmadev, size, aenq->entries, aenq->dma_addr);
+
+	efa_ah_cache_destroy(&edev->ah_cache);
 }
 
 /**
@@ -782,6 +784,12 @@ int efa_com_admin_init(struct efa_com_dev *edev,
 		return -ENODEV;
 	}
 
+	err = efa_ah_cache_init(&edev->ah_cache);
+	if (err) {
+		ibdev_err(edev->efa_dev, "Failed to init AH cache\n");
+		return err;
+	}
+
 	aq->depth = EFA_ADMIN_QUEUE_DEPTH;
 
 	aq->dmadev = edev->dmadev;
@@ -794,7 +802,7 @@ int efa_com_admin_init(struct efa_com_dev *edev,
 
 	err = efa_com_init_comp_ctxt(aq);
 	if (err)
-		return err;
+		goto err_destroy_ah_cache;
 
 	err = efa_com_admin_init_sq(edev);
 	if (err)
@@ -832,6 +840,8 @@ int efa_com_admin_init(struct efa_com_dev *edev,
 			  aq->sq.entries, aq->sq.dma_addr);
 err_destroy_comp_ctxt:
 	devm_kfree(edev->dmadev, aq->comp_ctx);
+err_destroy_ah_cache:
+	efa_ah_cache_destroy(&edev->ah_cache);
 
 	return err;
 }

drivers/infiniband/hw/efa/efa_com.h

@@ -14,6 +14,7 @@
 
 #include <rdma/ib_verbs.h>
 
+#include "efa_ah_cache.h"
 #include "efa_common_defs.h"
 #include "efa_admin_defs.h"
 #include "efa_admin_cmds_defs.h"
@@ -113,6 +114,8 @@ struct efa_com_dev {
 	u32 supported_features;
 	u32 dma_addr_bits;
 
+	struct efa_ah_cache ah_cache;
+
 	u32 dev_api_ver;
 	struct efa_com_mmio_read mmio_read;
 };