Re: [PATCH v3] powerpc/pseries: read the lpar name from the firmware

Hi Laurent,

Laurent Dufour [off-list ref] writes:

+/*
+ * PAPR defines, in section "7.3.16 System Parameters Option", the token 55 to
+ * read the LPAR name.
+ */
+#define SPLPAR_LPAR_NAME_TOKEN	55
+static void read_lpar_name(struct seq_file *m)
+{
+	int rc, len, token;
+	union {
+		char raw_buffer[RTAS_DATA_BUF_SIZE];
+		struct {
+			__be16 len;

This:

+			char name[RTAS_DATA_BUF_SIZE-2];

                                       ^^^^^^

should be 4000, not (4K - 2), according to PAPR (it's weird and I don't
know the reason).

+		};
+	} *local_buffer;
+
+	token = rtas_token("ibm,get-system-parameter");
+	if (token == RTAS_UNKNOWN_SERVICE)
+		return;
+
+	local_buffer = kmalloc(sizeof(*local_buffer), GFP_KERNEL);
+	if (!local_buffer)
+		return;
+
+	do {
+		spin_lock(&rtas_data_buf_lock);
+		memset(rtas_data_buf, 0, RTAS_DATA_BUF_SIZE);
+		rc = rtas_call(token, 3, 1, NULL, SPLPAR_LPAR_NAME_TOKEN,
+			       __pa(rtas_data_buf), RTAS_DATA_BUF_SIZE);
+		if (!rc)
+			memcpy(local_buffer->raw_buffer, rtas_data_buf,
+			       RTAS_DATA_BUF_SIZE);
+		spin_unlock(&rtas_data_buf_lock);
+	} while (rtas_busy_delay(rc));
+
+	if (rc != 0) {
+		pr_err_once(
+			"%s %s Error calling get-system-parameter (0x%x)\n",
+			__FILE__, __func__, rc);

The __FILE__ and __func__ in the message seem unnecessary, and rc should
be reported in decimal so the error meaning is apparent.

Is there a reasonable fallback for VMs where this parameter doesn't
exist? PowerVM partitions should always have it, but what do we want the
behavior to be on other hypervisors?

+	} else {
+		/* Force end of string */
+		len = be16_to_cpu(local_buffer->len);
+		if (len >= (RTAS_DATA_BUF_SIZE-2))
+			len = RTAS_DATA_BUF_SIZE-2;

Could use min() or clamp(), and it would be better to build the
expression using the value of sizeof(local_buffer->name).

+		local_buffer->name[len] = '\0';

If 'len' can be (RTAS_DATA_BUF_SIZE - 2), then this writes past the end
of the buffer, no?