[dpdk-stable] [PATCH] [18.11] net/mlx5: fix doorbell register mmap offset

[Viacheslav Ovsiienko <viacheslavo@nvidia.com>]

The rdma-core might support multiple doorbell registers within
single User Access Region page. The registers beside the first one
are considered as the children ones and it is supposed there is no
extra need to mmap them due the page is already mapped for the first
("parent") register and rdma-core provides uar_map_offset as zero
for the children registers. This caused the DPDK secondary process
crash [1] on mmap() attempt with zero offset parameter.

This patch provides the workaround, to perform correct mapping
in the secondary process we should find the uar_map_offset from
the parent register in the UAR page and use found non-zero one
for mapping.

[1] https://bugs.dpdk.org/show_bug.cgi?id=618

Fixes: 9d2cbd9ea8e7 ("net/mlx5: remove device register remap")
Cc: stable@dpdk.org

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>

--
Note: there was no patch "net/mlx5: remove device register remap"
in original 18.11, it was backported to 18.11 LTS later.
---
 drivers/net/mlx5/mlx5_txq.c | 52 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mlx5/mlx5_txq.c b/drivers/net/mlx5/mlx5_txq.c
index 089f9ab629..29e082ec86 100644
--- a/drivers/net/mlx5/mlx5_txq.c
+++ b/drivers/net/mlx5/mlx5_txq.c
@@ -257,6 +257,53 @@ txq_uar_init(struct mlx5_txq_ctrl *txq_ctrl)
 #endif
 }
 
+/**
+ * Find the Tx UAR mmap offset for the page containing the specified register.
+ *
+ * @param dev
+ *   Pointer to Ethernet device.
+ * @param bf
+ *   Pointer to doorbell register.
+ *
+ * @return
+ *   found mmap offset, 0 otherwise.
+ *
+ * The rdma-core might support multiple registers within one UAR page, the
+ * registers beside the first one are considered as the children and it is
+ * supposed there is no need to mmap them due the page is already mapped
+ * for the first ("parent") register. The uar_map_offset is zero for the
+ * child register, to perform mapping in the secondary process we should
+ * find the uar_map_offset from the parent and use one for mapping.
+ */
+static off_t
+mlx5_tx_find_uar_offset(struct rte_eth_dev *dev, void *bf)
+{
+	const size_t page_size = sysconf(_SC_PAGESIZE);
+	const uintptr_t reg = RTE_ALIGN_FLOOR((uintptr_t)bf, page_size);
+	const struct mlx5_priv *priv = dev->data->dev_private;
+	unsigned int i;
+
+	for (i = 0; i != priv->txqs_n; ++i) {
+		struct mlx5_txq_ctrl *txq_ctrl = mlx5_txq_get(dev, i);
+
+		if (!txq_ctrl)
+			continue;
+		if (txq_ctrl->uar_mmap_offset && txq_ctrl->bf_reg) {
+			uintptr_t tx_reg = RTE_ALIGN_FLOOR
+						((uintptr_t)txq_ctrl->bf_reg,
+						 page_size);
+			if (tx_reg == reg) {
+				off_t offset = txq_ctrl->uar_mmap_offset;
+
+				mlx5_txq_release(dev, i);
+				return offset;
+			}
+		}
+		mlx5_txq_release(dev, i);
+	}
+	return 0;
+}
+
 /**
  * Remap UAR register of a Tx queue for secondary process.
  *
@@ -584,7 +631,10 @@ mlx5_txq_ibv_new(struct rte_eth_dev *dev, uint16_t idx)
 	rte_atomic32_inc(&txq_ibv->refcnt);
 	txq_ctrl->bf_reg = qp.bf.reg;
 	if (qp.comp_mask & MLX5DV_QP_MASK_UAR_MMAP_OFFSET) {
-		txq_ctrl->uar_mmap_offset = qp.uar_mmap_offset;
+		txq_ctrl->uar_mmap_offset = qp.uar_mmap_offset ?
+					    qp.uar_mmap_offset :
+					    mlx5_tx_find_uar_offset
+						(dev, txq_ctrl->bf_reg);
 		DRV_LOG(DEBUG, "port %u: uar_mmap_offset 0x%"PRIx64,
 			dev->data->port_id, txq_ctrl->uar_mmap_offset);
 	} else {
-- 
2.18.1