linux-kernel - [PATCH for-next v4 2/2] RDMA/rxe: Enable asynchronous prefetch for ODP MRs

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Message-ID: <20250522111955.3227-3-dskmtsd@gmail.com>
Date: Thu, 22 May 2025 11:19:55 +0000
From: Daisuke Matsuda <dskmtsd@...il.com>
To: linux-kernel@...r.kernel.org,
	linux-rdma@...r.kernel.org,
	leon@...nel.org,
	jgg@...pe.ca,
	zyjzyj2000@...il.com
Cc: Daisuke Matsuda <dskmtsd@...il.com>
Subject: [PATCH for-next v4 2/2] RDMA/rxe: Enable asynchronous prefetch for ODP MRs

Calling ibv_advise_mr(3) with flags other than IBV_ADVISE_MR_FLAG_FLUSH
invokes an asynchronous request. It is best-effort, and thus can safely be
deferred to the system-wide workqueue.

The reference counter in rxe_mr is used to ensure that the MRs persist and
that rxe is not terminated until the queued work is done.

Signed-off-by: Daisuke Matsuda <dskmtsd@...il.com>
---
 drivers/infiniband/sw/rxe/rxe_odp.c | 81 ++++++++++++++++++++++++++++-
 1 file changed, 79 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
index c723d8a6cfec..2b112b07ec8c 100644
--- a/drivers/infiniband/sw/rxe/rxe_odp.c
+++ b/drivers/infiniband/sw/rxe/rxe_odp.c
@@ -423,6 +423,46 @@ enum resp_states rxe_odp_do_atomic_write(struct rxe_mr *mr, u64 iova, u64 value)
 	return RESPST_NONE;
 }
 
+struct prefetch_mr_work {
+	struct work_struct work;
+	u32 pf_flags;
+	u32 num_sge;
+	struct {
+		u64 io_virt;
+		struct rxe_mr *mr;
+		size_t length;
+	} frags[];
+};
+
+static void rxe_ib_prefetch_mr_work(struct work_struct *w)
+{
+	struct prefetch_mr_work *work =
+		container_of(w, struct prefetch_mr_work, work);
+	int ret;
+	u32 i;
+
+	/* We rely on IB/core that work is executed if we have num_sge != 0 only. */
+	WARN_ON(!work->num_sge);
+	for (i = 0; i < work->num_sge; ++i) {
+		struct ib_umem_odp *umem_odp;
+
+		ret = rxe_odp_do_pagefault_and_lock(work->frags[i].mr, work->frags[i].io_virt,
+						    work->frags[i].length, work->pf_flags);
+		if (ret < 0) {
+			rxe_dbg_mr(work->frags[i].mr, "failed to prefetch the mr\n");
+			goto deref;
+		}
+
+		umem_odp = to_ib_umem_odp(work->frags[i].mr->umem);
+		mutex_unlock(&umem_odp->umem_mutex);
+
+deref:
+		rxe_put(work->frags[i].mr);
+	}
+
+	kvfree(work);
+}
+
 static int rxe_ib_prefetch_sg_list(struct ib_pd *ibpd,
 				   enum ib_uverbs_advise_mr_advice advice,
 				   u32 pf_flags, struct ib_sge *sg_list,
@@ -472,7 +512,11 @@ static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
 				     enum ib_uverbs_advise_mr_advice advice,
 				     u32 flags, struct ib_sge *sg_list, u32 num_sge)
 {
+	struct rxe_pd *pd = container_of(ibpd, struct rxe_pd, ibpd);
 	u32 pf_flags = RXE_PAGEFAULT_DEFAULT;
+	struct prefetch_mr_work *work;
+	struct rxe_mr *mr;
+	u32 i;
 
 	if (advice == IB_UVERBS_ADVISE_MR_ADVICE_PREFETCH)
 		pf_flags |= RXE_PAGEFAULT_RDONLY;
@@ -485,8 +529,41 @@ static int rxe_ib_advise_mr_prefetch(struct ib_pd *ibpd,
 		return rxe_ib_prefetch_sg_list(ibpd, advice, pf_flags, sg_list,
 					       num_sge);
 
-	/* Asynchronous call is to be added in the next patch */
-	return -EOPNOTSUPP;
+	/* Asynchronous call is "best-effort" and allowed to fail */
+	work = kvzalloc(struct_size(work, frags, num_sge), GFP_KERNEL);
+	if (!work)
+		return -ENOMEM;
+
+	INIT_WORK(&work->work, rxe_ib_prefetch_mr_work);
+	work->pf_flags = pf_flags;
+	work->num_sge = num_sge;
+
+	for (i = 0; i < num_sge; ++i) {
+		/* takes a reference, which will be released in the queued work */
+		mr = lookup_mr(pd, IB_ACCESS_LOCAL_WRITE,
+			       sg_list[i].lkey, RXE_LOOKUP_LOCAL);
+		if (IS_ERR(mr))
+			goto err;
+
+		work->frags[i].io_virt = sg_list[i].addr;
+		work->frags[i].length = sg_list[i].length;
+		work->frags[i].mr = mr;
+	}
+
+	queue_work(system_unbound_wq, &work->work);
+
+	return 0;
+
+ err:
+	/* rollback reference counts for the invalid request */
+	while (i > 0) {
+		i--;
+		rxe_put(work->frags[i].mr);
+	}
+
+	kvfree(work);
+
+	return PTR_ERR(mr);
 }
 
 int rxe_ib_advise_mr(struct ib_pd *ibpd,
-- 
2.43.0