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

Daisuke Matsuda
2025-05-22T11:20:24Z

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@gmail.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