RDMA/efa: User/kernel compatibility handshake mechanism

Introduce a mechanism that performs an handshake between the userspace
provider and kernel driver which verifies that the user supports all
required features in order to operate correctly.

The handshake verifies the needed functionality by comparing the reported
device caps and the provider caps. If the device reports a non-zero
capability the appropriate comp mask is required from the userspace
provider in order to allocate the context.

Link: https://lore.kernel.org/r/20200722140312.3651-4-galpress@amazon.comReviewed-by: Shadi Ammouri <sammouri@amazon.com>
Reviewed-by: Yossi Leybovich <sleybo@amazon.com>
Signed-off-by: Gal Pressman <galpress@amazon.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/efa/efa_verbs.c

@@ -1501,11 +1501,39 @@ static int efa_dealloc_uar(struct efa_dev *dev, u16 uarn)
 	return efa_com_dealloc_uar(&dev->edev, &params);
 }
 
+#define EFA_CHECK_USER_COMP(_dev, _comp_mask, _attr, _mask, _attr_str) \
+	(_attr_str = (!(_dev)->dev_attr._attr || ((_comp_mask) & (_mask))) ? \
+		     NULL : #_attr)
+
+static int efa_user_comp_handshake(const struct ib_ucontext *ibucontext,
+				   const struct efa_ibv_alloc_ucontext_cmd *cmd)
+{
+	struct efa_dev *dev = to_edev(ibucontext->device);
+	char *attr_str;
+
+	if (EFA_CHECK_USER_COMP(dev, cmd->comp_mask, max_tx_batch,
+				EFA_ALLOC_UCONTEXT_CMD_COMP_TX_BATCH, attr_str))
+		goto err;
+
+	if (EFA_CHECK_USER_COMP(dev, cmd->comp_mask, min_sq_depth,
+				EFA_ALLOC_UCONTEXT_CMD_COMP_MIN_SQ_WR,
+				attr_str))
+		goto err;
+
+	return 0;
+
+err:
+	ibdev_dbg(&dev->ibdev, "Userspace handshake failed for %s attribute\n",
+		  attr_str);
+	return -EOPNOTSUPP;
+}
+
 int efa_alloc_ucontext(struct ib_ucontext *ibucontext, struct ib_udata *udata)
 {
 	struct efa_ucontext *ucontext = to_eucontext(ibucontext);
 	struct efa_dev *dev = to_edev(ibucontext->device);
 	struct efa_ibv_alloc_ucontext_resp resp = {};
+	struct efa_ibv_alloc_ucontext_cmd cmd = {};
 	struct efa_com_alloc_uar_result result;
 	int err;
 
@@ -1514,6 +1542,18 @@ int efa_alloc_ucontext(struct ib_ucontext *ibucontext, struct ib_udata *udata)
 	 * we will ack input fields in our response.
 	 */
 
+	err = ib_copy_from_udata(&cmd, udata,
+				 min(sizeof(cmd), udata->inlen));
+	if (err) {
+		ibdev_dbg(&dev->ibdev,
+			  "Cannot copy udata for alloc_ucontext\n");
+		goto err_out;
+	}
+
+	err = efa_user_comp_handshake(ibucontext, &cmd);
+	if (err)
+		goto err_out;
+
 	err = efa_com_alloc_uar(&dev->edev, &result);
 	if (err)
 		goto err_out;

include/uapi/rdma/efa-abi.h

@@ -20,6 +20,16 @@
  * hex bit offset of the field.
  */
 
+enum {
+	EFA_ALLOC_UCONTEXT_CMD_COMP_TX_BATCH  = 1 << 0,
+	EFA_ALLOC_UCONTEXT_CMD_COMP_MIN_SQ_WR = 1 << 1,
+};
+
+struct efa_ibv_alloc_ucontext_cmd {
+	__u32 comp_mask;
+	__u8 reserved_20[4];
+};
+
 enum efa_ibv_user_cmds_supp_udata {
 	EFA_USER_CMDS_SUPP_UDATA_QUERY_DEVICE = 1 << 0,
 	EFA_USER_CMDS_SUPP_UDATA_CREATE_AH    = 1 << 1,