cxl/hdm: Fail upon detecting 0-sized decoders

Decoders committed with 0-size lead to later crashes on shutdown as
__cxl_dpa_release() assumes a 'struct resource' has been established in
the in 'cxlds->dpa_res'. Just fail the driver load in this instance
since there are deeper problems with the enumeration or the setup when
this happens.

Fixes: 9c57cde ("cxl/hdm: Enumerate allocated DPA")
Cc: <stable@vger.kernel.org>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://lore.kernel.org/r/168149843516.792294.11872242648319572632.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Author: djbw

drivers/cxl/core/hdm.c

@@ -269,8 +269,11 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 
 	lockdep_assert_held_write(&cxl_dpa_rwsem);
 
-	if (!len)
-		goto success;
+	if (!len) {
+		dev_warn(dev, "decoder%d.%d: empty reservation attempted\n",
+			 port->id, cxled->cxld.id);
+		return -EINVAL;
+	}
 
 	if (cxled->dpa_res) {
 		dev_dbg(dev, "decoder%d.%d: existing allocation %pr assigned\n",
@@ -323,7 +326,6 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 		cxled->mode = CXL_DECODER_MIXED;
 	}
 
-success:
 	port->hdm_end++;
 	get_device(&cxled->cxld.dev);
 	return 0;
@@ -833,6 +835,13 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
 				 port->id, cxld->id);
 			return -ENXIO;
 		}
+
+		if (size == 0) {
+			dev_warn(&port->dev,
+				 "decoder%d.%d: Committed with zero size\n",
+				 port->id, cxld->id);
+			return -ENXIO;
+		}
 		port->commit_end = cxld->id;
 	} else {
 		/* unless / until type-2 drivers arrive, assume type-3 */