rdma_rxe: Stop passing AV from user space

This patch shows it is possible to replace the current
method used by rdma_rxe to handle UD transport where
user space creates and then passes an rxe_av *av to the
kernel driver as part of each rxe_send_wqe.

Here user space passes the handle created by the call to
ibv_create_ah in the send wqe. The kernel driver uses that
handle to get a pointer to the 'real' rxe_av that was
created in the kernel by the create ah verb.

To do this requires executing code in the driver that mimics
what is done in rdma_core to convert handles to objects.
This is not ideal but gets the job done. It would probably be
better for rdma_core to provide a service that can do this
for software drivers that have to do this.

The alternative (used by the MW code) is to create a driver
private index and pass that back from the create verb to
user space and then have user space use that in the send wqe.

I would like to avoid replicating work already being done by
rdma core by using the handle that already exists. I don't
know the relative performance of the lookup in rdma_core and
the red black tree used by rxe currently.

There is a matching change to provider/rxe.

Signed-off-by: Bob Pearson <rpearson@hpe.com>

drivers/infiniband/core/rdma_core.c

@@ -436,6 +436,7 @@ struct ib_uobject *rdma_lookup_get_uobject(const struct uverbs_api_object *obj,
 	uverbs_uobject_put(uobj);
 	return ERR_PTR(ret);
 }
+EXPORT_SYMBOL(rdma_lookup_get_uobject);
 
 static struct ib_uobject *
 alloc_begin_idr_uobject(const struct uverbs_api_object *obj,
@@ -726,6 +727,7 @@ void rdma_lookup_put_uobject(struct ib_uobject *uobj,
 	/* Pairs with the kref obtained by type->lookup_get */
 	uverbs_uobject_put(uobj);
 }
+EXPORT_SYMBOL(rdma_lookup_put_uobject);
 
 void setup_ufile_idr_uobject(struct ib_uverbs_file *ufile)
 {

drivers/infiniband/sw/rxe/rxe_av.c

@@ -33,6 +33,8 @@
 
 #include "rxe.h"
 #include "rxe_loc.h"
+#include "../../core/uverbs.h"
+#include "../../core/rdma_core.h"
 
 void rxe_init_av(struct rdma_ah_attr *attr, struct rxe_av *av)
 {
@@ -99,13 +101,50 @@ void rxe_av_fill_ip_info(struct rxe_av *av, struct rdma_ah_attr *attr)
 	av->network_type = rdma_gid_attr_network_type(sgid_attr);
 }
 
+static struct ib_ah *get_ah_from_handle(struct rxe_qp *qp, u32 handle)
+{
+	struct ib_uverbs_file *ufile;
+	struct uverbs_api *uapi;
+	const struct uverbs_api_object *type;
+	struct ib_uobject *uobj;
+
+	ufile = qp->ibqp.uobject->uevent.uobject.ufile;
+	uapi = ufile->device->uapi;
+	type = uapi_get_object(uapi, UVERBS_OBJECT_AH);
+	if (IS_ERR(type))
+		return NULL;
+	uobj = rdma_lookup_get_uobject(type, ufile, (s64)handle,
+				       UVERBS_LOOKUP_READ, NULL);
+	if (IS_ERR(uobj)) {
+		pr_warn("unable to lookup ah handle\n");
+		return NULL;
+	}
+
+	rdma_lookup_put_uobject(uobj, UVERBS_LOOKUP_READ);
+	return uobj->object;
+}
+
 struct rxe_av *rxe_get_av(struct rxe_pkt_info *pkt)
 {
-	if (!pkt || !pkt->qp)
+	struct rxe_qp *qp = pkt->qp;
+	struct rxe_send_wqe *wqe = pkt->wqe;
+	u32 handle;
+	struct ib_ah *ibah;
+	struct rxe_ah *ah;
+
+	if (!pkt || !qp)
 		return NULL;
 
-	if (qp_type(pkt->qp) == IB_QPT_RC || qp_type(pkt->qp) == IB_QPT_UC)
-		return &pkt->qp->pri_av;
+	if (qp_type(qp) == IB_QPT_RC || qp_type(qp) == IB_QPT_UC)
+		return &qp->pri_av;
+
+	if (qp->is_user) {
+		handle = wqe->wr.wr.ud.ah_handle;
+		ibah = get_ah_from_handle(qp, handle);
+	} else {
+		ibah = wqe->wr.wr.ud.ah;
+	}
 
-	return (pkt->wqe) ? &pkt->wqe->av : NULL;
+	ah = to_rah(ibah);
+	return &ah->av;
 }

drivers/infiniband/sw/rxe/rxe_req.c

@@ -407,6 +407,10 @@ static struct sk_buff *init_req_packet(struct rxe_qp *qp,
 
 	/* init skb */
 	av = rxe_get_av(pkt);
+	if (!av) {
+		pr_warn("unable to get av\n");
+		return NULL;
+	}
 	skb = rxe_init_packet(rxe, av, paylen, pkt);
 	if (unlikely(!skb))
 		return NULL;

drivers/infiniband/sw/rxe/rxe_verbs.c

@@ -530,6 +530,7 @@ static void init_send_wr(struct rxe_qp *qp, struct rxe_send_wr *wr,
 	if (qp_type(qp) == IB_QPT_UD ||
 	    qp_type(qp) == IB_QPT_SMI ||
 	    qp_type(qp) == IB_QPT_GSI) {
+		wr->wr.ud.ah = ud_wr(ibwr)->ah;
 		wr->wr.ud.remote_qpn = ud_wr(ibwr)->remote_qpn;
 		wr->wr.ud.remote_qkey = ud_wr(ibwr)->remote_qkey;
 		if (qp_type(qp) == IB_QPT_GSI)
@@ -586,11 +587,6 @@ static int init_send_wqe(struct rxe_qp *qp, const struct ib_send_wr *ibwr,
 
 	init_send_wr(qp, &wqe->wr, ibwr);
 
-	if (qp_type(qp) == IB_QPT_UD ||
-	    qp_type(qp) == IB_QPT_SMI ||
-	    qp_type(qp) == IB_QPT_GSI)
-		memcpy(&wqe->av, &to_rah(ud_wr(ibwr)->ah)->av, sizeof(wqe->av));
-
 	if (unlikely(ibwr->send_flags & IB_SEND_INLINE)) {
 		p = wqe->dma.inline_data;
 

include/uapi/rdma/rdma_user_rxe.h

@@ -89,6 +89,10 @@ struct rxe_send_wr {
 			__u32	reserved;
 		} atomic;
 		struct {
+			union {
+				__aligned_u64 ah_handle;
+				struct ib_ah *ah;
+			};
 			__u32	remote_qpn;
 			__u32	remote_qkey;
 			__u16	pkey_index;
@@ -132,7 +136,6 @@ struct rxe_dma_info {
 
 struct rxe_send_wqe {
 	struct rxe_send_wr	wr;
-	struct rxe_av		av;
 	__u32			status;
 	__u32			state;
 	__aligned_u64		iova;