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octeontx2-af: npc: cn20k: virtual index support

This patch adds virtual MCAM index allocation support for CN20K,
enabling defragmentation by allowing entries to be moved while
maintaining stable virtual indexes for callers.

[ ... ]

+static int npc_vidx_maps_modify(struct rvu *rvu, u16 vidx, u16 new_midx)
+{
+	u16 old_midx;
+	void *map;
+	int rc;
+
+	if (!npc_is_vidx(vidx)) {
+		dev_err(rvu->dev,
+			"%s: vidx(%u) does not map to proper mcam idx\n",
+			__func__, vidx);
+		return -ESRCH;
+	}
+
+	map = xa_erase(&npc_priv.xa_vidx2idx_map, vidx);
+	if (!map) {
+		dev_err(rvu->dev,
+			"%s: vidx(%u) could not be deleted from vidx2idx map\n",
+			__func__, vidx);
+		return -ESRCH;
+	}
+
+	old_midx = xa_to_value(map);
+
+	rc = xa_insert(&npc_priv.xa_vidx2idx_map, vidx,
+		       xa_mk_value(new_midx), GFP_KERNEL);
+	if (rc) {
+		dev_err(rvu->dev,
+			"%s: vidx(%u) cannot be added to vidx2idx map\n",
+			__func__, vidx);
+		goto fail1;
+	}
+
+	map = xa_erase(&npc_priv.xa_idx2vidx_map, old_midx);
+	if (!map) {
+		dev_err(rvu->dev,
+			"%s: old_midx(%u, vidx(%u)) cannot be added to idx2vidx map\n",
+			__func__, old_midx, vidx);
+		rc = -ESRCH;
+		goto fail2;
+	}
+
+	rc = xa_insert(&npc_priv.xa_idx2vidx_map, new_midx,
+		       xa_mk_value(vidx), GFP_KERNEL);
+	if (rc) {
+		dev_err(rvu->dev,
+			"%s: new_midx(%u, vidx(%u)) cannot be added to idx2vidx map\n",
+			__func__, new_midx, vidx);
+		goto fail3;
+	}
+
+	return 0;
+
+fail3:
+	if (xa_insert(&npc_priv.xa_idx2vidx_map, old_midx,
+		      xa_mk_value(vidx), GFP_KERNEL))
+		dev_err(rvu->dev,
+			"%s: Error to roll back idx2vidx old_midx=%u vidx=%u\n",
+			__func__, old_midx, vidx);
+fail2:
+	if (xa_erase(&npc_priv.xa_vidx2idx_map, vidx))
+		dev_err(rvu->dev,
+			"%s: Failed to roll back vidx2idx vidx=%u\n",
+			__func__, vidx);
+
+fail1:
+	if (xa_insert(&npc_priv.xa_idx2vidx_map, old_midx,
+		      xa_mk_value(vidx), GFP_KERNEL))

The rollback at fail1 appears to operate on the wrong XArray. When
xa_insert() fails above and we jump to fail1, the xa_idx2vidx_map still
contains old_midx since the erase of xa_idx2vidx_map has not executed yet.
This xa_insert() will return -EBUSY because the key already exists.

Should this instead restore vidx to xa_vidx2idx_map with the original
old_midx value, since that was the map modified before the failure?

+		dev_err(rvu->dev,
+			"%s: Faled to roll back idx2vidx to old_midx=%u, vidx=%u\n",
+			__func__, old_midx, vidx);
+
+	return rc;
+}

[ ... ]