RDMA/bnxt_re: Avoid repeated requests to allocate WC pages

Applications can request multiple WC pages for the same ucontext.
As of now, only 1 WC page per ucontext is supported. Add a lock to
avoid concurrent access and a check to fail repeated requests.
Also, if the mmap entry insert fails for the WC, free the Doorbell
page index mapped for the WC page.

Fixes: eee6268421a2 ("RDMA/bnxt_re: Move the UAPI methods to a dedicated file")
Fixes: 360da60d6c6e ("RDMA/bnxt_re: Enable low latency push")
Link: https://patch.msgid.link/r/20260615224751.232802-12-selvin.xavier@broadcom.com
Reviewed-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

3 files changed, 29 insertions, 6 deletions

diff --git a/drivers/infiniband/hw/bnxt_re/ib_verbs.c b/drivers/infiniband/hw/bnxt_re/ib_verbs.c
index c3570bf0204f..565762529007 100644
--- a/drivers/infiniband/hw/bnxt_re/ib_verbs.c
+++ b/drivers/infiniband/hw/bnxt_re/ib_verbs.c
@@ -4770,6 +4770,7 @@ int bnxt_re_alloc_ucontext(struct ib_ucontext *ctx, struct ib_udata *udata)
 		goto fail;
 	}
 	spin_lock_init(&uctx->sh_lock);
+	mutex_init(&uctx->wcdpi_lock);
 
 	resp.comp_mask = BNXT_RE_UCNTX_CMASK_HAVE_CCTX;
 	chip_met_rev_num = rdev->chip_ctx->chip_num;
diff --git a/drivers/infiniband/hw/bnxt_re/ib_verbs.h b/drivers/infiniband/hw/bnxt_re/ib_verbs.h
index 4d6d1259a795..22bf81668cfb 100644
--- a/drivers/infiniband/hw/bnxt_re/ib_verbs.h
+++ b/drivers/infiniband/hw/bnxt_re/ib_verbs.h
@@ -143,6 +143,7 @@ struct bnxt_re_ucontext {
 	struct bnxt_re_dev	*rdev;
 	struct bnxt_qplib_dpi	dpi;
 	struct bnxt_qplib_dpi   wcdpi;
+	struct mutex		wcdpi_lock;	/* serialises WC DPI alloc/free */
 	void			*shpg;
 	spinlock_t		sh_lock;	/* protect shpg */
 	struct rdma_user_mmap_entry *shpage_mmap;
diff --git a/drivers/infiniband/hw/bnxt_re/uapi.c b/drivers/infiniband/hw/bnxt_re/uapi.c
index b9922360f11b..7e5a55d29076 100644
--- a/drivers/infiniband/hw/bnxt_re/uapi.c
+++ b/drivers/infiniband/hw/bnxt_re/uapi.c
@@ -98,14 +98,23 @@ static int UVERBS_HANDLER(BNXT_RE_METHOD_ALLOC_PAGE)(struct uverbs_attr_bundle *
 
 	switch (alloc_type) {
 	case BNXT_RE_ALLOC_WC_PAGE:
-		if (cctx->modes.db_push)  {
+		if (cctx->modes.db_push) {
+			mutex_lock(&uctx->wcdpi_lock);
+			/* already allocated — one WC page per context */
+			if (uctx->wcdpi.dbr) {
+				mutex_unlock(&uctx->wcdpi_lock);
+				return -EEXIST;
+			}
 			if (bnxt_qplib_alloc_dpi(&rdev->qplib_res, &uctx->wcdpi,
-						 uctx, BNXT_QPLIB_DPI_TYPE_WC))
+						 uctx, BNXT_QPLIB_DPI_TYPE_WC)) {
+				mutex_unlock(&uctx->wcdpi_lock);
 				return -ENOMEM;
+			}
 			length = PAGE_SIZE;
 			dpi = uctx->wcdpi.dpi;
 			addr = (u64)uctx->wcdpi.umdbr;
 			mmap_flag = BNXT_RE_MMAP_WC_DB;
+			mutex_unlock(&uctx->wcdpi_lock);
 		} else {
 			return -EINVAL;
 		}
@@ -128,8 +137,15 @@ static int UVERBS_HANDLER(BNXT_RE_METHOD_ALLOC_PAGE)(struct uverbs_attr_bundle *
 	}
 
 	entry = bnxt_re_mmap_entry_insert(uctx, addr, mmap_flag, &mmap_offset);
-	if (!entry)
+	if (!entry) {
+		if (mmap_flag == BNXT_RE_MMAP_WC_DB) {
+			mutex_lock(&uctx->wcdpi_lock);
+			bnxt_qplib_dealloc_dpi(&rdev->qplib_res, &uctx->wcdpi);
+			uctx->wcdpi.dbr = NULL;
+			mutex_unlock(&uctx->wcdpi_lock);
+		}
 		return -ENOMEM;
+	}
 
 	uobj->object = entry;
 	uverbs_finalize_uobj_create(attrs, BNXT_RE_ALLOC_PAGE_HANDLE);
@@ -160,11 +176,16 @@ static int alloc_page_obj_cleanup(struct ib_uobject *uobject,
 
 	switch (entry->mmap_flag) {
 	case BNXT_RE_MMAP_WC_DB:
-		if (uctx && uctx->wcdpi.dbr) {
+		if (uctx) {
 			struct bnxt_re_dev *rdev = uctx->rdev;
 
-			bnxt_qplib_dealloc_dpi(&rdev->qplib_res, &uctx->wcdpi);
-			uctx->wcdpi.dbr = NULL;
+			mutex_lock(&uctx->wcdpi_lock);
+			if (uctx->wcdpi.dbr) {
+				bnxt_qplib_dealloc_dpi(&rdev->qplib_res,
+						       &uctx->wcdpi);
+				uctx->wcdpi.dbr = NULL;
+			}
+			mutex_unlock(&uctx->wcdpi_lock);
 		}
 		break;
 	case BNXT_RE_MMAP_DBR_BAR: