[PATCH] cxl/pci: Get rid of pointer arithmetic reading CDAT table

[Robert Richter]

Reading the CDAT table using DOE requires a Table Access Response
Header in addition to the CDAT entry. In current implementation this
has caused offsets with sizeof(__le32) to the actual buffers. This led
to hardly readable code and even bugs (see fix of devm_kfree() in
read_cdat_data()).

Rework code to avoid calculations with sizeof(__le32). Introduce
struct cdat_doe for this which contains the Table Access Response
Header and a variable payload size for various data structures
afterwards to access the CDAT table and its CDAT Data Structures
without recalculating buffer offsets.

Cc: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Fan Ni <nifan.cxl@xxxxxxxxx>
Signed-off-by: Robert Richter <rrichter@xxxxxxx>
---
 drivers/cxl/core/pci.c | 80 ++++++++++++++++++++----------------------
 drivers/cxl/cxlpci.h   | 19 ++++++++++
 2 files changed, 57 insertions(+), 42 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index 5aaa0b36c42a..f900740c6dea 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -517,14 +517,14 @@ EXPORT_SYMBOL_NS_GPL(cxl_hdm_decode_init, CXL);
 	 FIELD_PREP(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, (entry_handle)))
 
 static int cxl_cdat_get_length(struct device *dev,
-			       struct pci_doe_mb *cdat_doe,
+			       struct pci_doe_mb *doe_mb,
 			       size_t *length)
 {
 	__le32 request = CDAT_DOE_REQ(0);
 	__le32 response[2];
 	int rc;
 
-	rc = pci_doe(cdat_doe, PCI_DVSEC_VENDOR_ID_CXL,
+	rc = pci_doe(doe_mb, PCI_DVSEC_VENDOR_ID_CXL,
 		     CXL_DOE_PROTOCOL_TABLE_ACCESS,
 		     &request, sizeof(request),
 		     &response, sizeof(response));
@@ -542,56 +542,54 @@ static int cxl_cdat_get_length(struct device *dev,
 }
 
 static int cxl_cdat_read_table(struct device *dev,
-			       struct pci_doe_mb *cdat_doe,
-			       void *cdat_table, size_t *cdat_length)
+			       struct pci_doe_mb *doe_mb,
+			       struct cdat_doe *doe, size_t *length)
 {
-	size_t length = *cdat_length + sizeof(__le32);
-	__le32 *data = cdat_table;
+	size_t received, remaining = *length;
 	int entry_handle = 0;
 	__le32 saved_dw = 0;
 
 	do {
 		__le32 request = CDAT_DOE_REQ(entry_handle);
-		struct cdat_entry_header *entry;
-		size_t entry_dw;
 		int rc;
 
-		rc = pci_doe(cdat_doe, PCI_DVSEC_VENDOR_ID_CXL,
+		rc = pci_doe(doe_mb, PCI_DVSEC_VENDOR_ID_CXL,
 			     CXL_DOE_PROTOCOL_TABLE_ACCESS,
 			     &request, sizeof(request),
-			     data, length);
+			     doe, sizeof(*doe) + remaining);
 		if (rc < 0) {
 			dev_err(dev, "DOE failed: %d", rc);
 			return rc;
 		}
 
-		/* 1 DW Table Access Response Header + CDAT entry */
-		entry = (struct cdat_entry_header *)(data + 1);
+		if (rc < sizeof(*doe))
+			return -EIO;
+
+		received = rc - sizeof(*doe);
+
 		if ((entry_handle == 0 &&
-		     rc != sizeof(__le32) + sizeof(struct cdat_header)) ||
+		     received != sizeof(doe->header[0])) ||
 		    (entry_handle > 0 &&
-		     (rc < sizeof(__le32) + sizeof(*entry) ||
-		      rc != sizeof(__le32) + le16_to_cpu(entry->length))))
+		     (received < sizeof(doe->entry[0]) ||
+		      received != le16_to_cpu(doe->entry->length))))
 			return -EIO;
 
 		/* Get the CXL table access header entry handle */
 		entry_handle = FIELD_GET(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE,
-					 le32_to_cpu(data[0]));
-		entry_dw = rc / sizeof(__le32);
-		/* Skip Header */
-		entry_dw -= 1;
+					 le32_to_cpu(doe->doe_header));
+
 		/*
 		 * Table Access Response Header overwrote the last DW of
 		 * previous entry, so restore that DW
 		 */
-		*data = saved_dw;
-		length -= entry_dw * sizeof(__le32);
-		data += entry_dw;
-		saved_dw = *data;
+		doe->doe_header = saved_dw;
+		remaining -= received;
+		doe = (void *)doe + received;
+		saved_dw = doe->doe_header;
 	} while (entry_handle != CXL_DOE_TABLE_ACCESS_LAST_ENTRY);
 
 	/* Length in CDAT header may exceed concatenation of CDAT entries */
-	*cdat_length -= length - sizeof(__le32);
+	*length -= remaining;
 
 	return 0;
 }
@@ -616,11 +614,11 @@ void read_cdat_data(struct cxl_port *port)
 {
 	struct device *uport = port->uport_dev;
 	struct device *dev = &port->dev;
-	struct pci_doe_mb *cdat_doe;
+	struct pci_doe_mb *doe_mb;
 	struct pci_dev *pdev = NULL;
 	struct cxl_memdev *cxlmd;
-	size_t cdat_length;
-	void *cdat_table, *cdat_buf;
+	struct cdat_doe *doe;
+	size_t length;
 	int rc;
 
 	if (is_cxl_memdev(uport)) {
@@ -637,40 +635,38 @@ void read_cdat_data(struct cxl_port *port)
 	if (!pdev)
 		return;
 
-	cdat_doe = pci_find_doe_mailbox(pdev, PCI_DVSEC_VENDOR_ID_CXL,
-					CXL_DOE_PROTOCOL_TABLE_ACCESS);
-	if (!cdat_doe) {
+	doe_mb = pci_find_doe_mailbox(pdev, PCI_DVSEC_VENDOR_ID_CXL,
+				      CXL_DOE_PROTOCOL_TABLE_ACCESS);
+	if (!doe_mb) {
 		dev_dbg(dev, "No CDAT mailbox\n");
 		return;
 	}
 
 	port->cdat_available = true;
 
-	if (cxl_cdat_get_length(dev, cdat_doe, &cdat_length)) {
+	if (cxl_cdat_get_length(dev, doe_mb, &length)) {
 		dev_dbg(dev, "No CDAT length\n");
 		return;
 	}
 
-	cdat_buf = devm_kzalloc(dev, cdat_length + sizeof(__le32),
-				  GFP_KERNEL);
-	if (!cdat_buf)
-		return;
+	doe = devm_kzalloc(dev, sizeof(*doe) + length, GFP_KERNEL);
+	if (!doe)
+		goto err;
 
-	rc = cxl_cdat_read_table(dev, cdat_doe, cdat_buf, &cdat_length);
+	rc = cxl_cdat_read_table(dev, doe_mb, doe, &length);
 	if (rc)
 		goto err;
 
-	cdat_table = cdat_buf + sizeof(__le32);
-	if (cdat_checksum(cdat_table, cdat_length))
+	if (cdat_checksum(doe->table, length))
 		goto err;
 
-	port->cdat.table = cdat_table;
-	port->cdat.length = cdat_length;
-	return;
+	port->cdat.table = doe->table;
+	port->cdat.length = length;
 
+	return;
 err:
 	/* Don't leave table data allocated on error */
-	devm_kfree(dev, cdat_buf);
+	devm_kfree(dev, doe);
 	dev_err(dev, "Failed to read/validate CDAT.\n");
 }
 EXPORT_SYMBOL_NS_GPL(read_cdat_data, CXL);
diff --git a/drivers/cxl/cxlpci.h b/drivers/cxl/cxlpci.h
index 0fa4799ea316..d12ed9d8dec1 100644
--- a/drivers/cxl/cxlpci.h
+++ b/drivers/cxl/cxlpci.h
@@ -85,6 +85,25 @@ struct cdat_entry_header {
 	__le16 length;
 } __packed;
 
+/*
+ * Response contains the CDAT only response header of the DOE. The
+ * response payload is a CDAT structure (either CDAT header or entry),
+ * it may also mark the beginning of the CDAT table.
+ *
+ * Spec refs:
+ *
+ * CXL 3.1 Table 8-14: Read Entry Response
+ * CDAT Specification 1.03: 2 CDAT Data Structures
+ */
+struct cdat_doe {
+	__le32 doe_header;
+	union {
+		u8 table[0];
+		struct cdat_header header[0];
+		struct cdat_entry_header entry[0];
+	};
+} __packed;
+
 int devm_cxl_port_enumerate_dports(struct cxl_port *port);
 struct cxl_dev_state;
 int cxl_hdm_decode_init(struct cxl_dev_state *cxlds, struct cxl_hdm *cxlhdm,
-- 
2.39.2