Hello,

On Fri, Nov 17, 2023 at 11:14:27PM -0600, Nathan Lynch via B4 Relay wrote:

From: Nathan Lynch <redacted>

PowerVM LPARs may retrieve Vital Product Data (VPD) for system
components using the ibm,get-vpd RTAS function.

We can expose this to user space with a /dev/papr-vpd character
device, where the programming model is:

  struct papr_location_code plc = { .str = "", }; /* obtain all VPD */
  int devfd = open("/dev/papr-vpd", O_RDONLY);
  int vpdfd = ioctl(devfd, PAPR_VPD_CREATE_HANDLE, &plc);
  size_t size = lseek(vpdfd, 0, SEEK_END);
  char *buf = malloc(size);
  pread(devfd, buf, size, 0);

When a file descriptor is obtained from ioctl(PAPR_VPD_CREATE_HANDLE),
the file contains the result of a complete ibm,get-vpd sequence. The
file contents are immutable from the POV of user space. To get a new
view of the VPD, the client must create a new handle.

This design choice insulates user space from most of the complexities
that ibm,get-vpd brings:

* ibm,get-vpd must be called more than once to obtain complete
  results.

* Only one ibm,get-vpd call sequence should be in progress at a time;
  interleaved sequences will disrupt each other. Callers must have a
  protocol for serializing their use of the function.

* A call sequence in progress may receive a "VPD changed, try again"
  status, requiring the client to abandon the sequence and start
  over.

The memory required for the VPD buffers seems acceptable, around 20KB
for all VPD on one of my systems. And the value of the
/rtas/ibm,vpd-size DT property (the estimated maximum size of VPD) is
consistently 300KB across various systems I've checked.

I've implemented support for this new ABI in the rtas_get_vpd()
function in librtas, which the vpdupdate command currently uses to
populate its VPD database. I've verified that an unmodified vpdupdate
binary generates an identical database when using a librtas.so that
prefers the new ABI.

Note that the driver needs to serialize its call sequences with legacy
sys_rtas(ibm,get-vpd) callers, so it exposes its internal lock for
sys_rtas.

Signed-off-by: Nathan Lynch <redacted>
---
 Documentation/userspace-api/ioctl/ioctl-number.rst |   2 +
 arch/powerpc/include/uapi/asm/papr-vpd.h           |  22 +
 arch/powerpc/platforms/pseries/Makefile            |   1 +
 arch/powerpc/platforms/pseries/papr-vpd.c          | 536 +++++++++++++++++++++
 4 files changed, 561 insertions(+)

...

+/**
+ * papr_vpd_retrieve() - Return the VPD for a location code.
+ * @loc_code: Location code that defines the scope of VPD to return.
+ *
+ * Run VPD sequences against @loc_code until a blob is successfully
+ * instantiated, or a hard error is encountered, or a fatal signal is
+ * pending.
+ *
+ * Context: May sleep.
+ * Return: A fully populated VPD blob when successful. Encoded error
+ * pointer otherwise.
+ */
+static const struct vpd_blob *papr_vpd_retrieve(const struct papr_location_code *loc_code)
+{
+	const struct vpd_blob *blob;
+
+	/*
+	 * EAGAIN means the sequence errored with a -4 (VPD changed)
+	 * status from ibm,get-vpd, and we should attempt a new
+	 * sequence. PAPR+ R1–7.3.20–5 indicates that this should be a
+	 * transient condition, not something that happens
+	 * continuously. But we'll stop trying on a fatal signal.
+	 */
+	do {
+		blob = papr_vpd_run_sequence(loc_code);
+		if (!IS_ERR(blob)) /* Success. */
+			break;
+		if (PTR_ERR(blob) != -EAGAIN) /* Hard error. */
+			break;
+		pr_info_ratelimited("VPD changed during retrieval, retrying\n");
+		cond_resched();
+	} while (!fatal_signal_pending(current));

this is defined in linux/sched/signal.h which is not included.

+
+	return blob;
+}
+
+static ssize_t papr_vpd_handle_read(struct file *file, char __user *buf, size_t size, loff_t *off)
+{
+	const struct vpd_blob *blob = file->private_data;
+
+	/* bug: we should not instantiate a handle without any data attached. */
+	if (!vpd_blob_has_data(blob)) {
+		pr_err_once("handle without data\n");
+		return -EIO;
+	}
+
+	return simple_read_from_buffer(buf, size, off, blob->data, blob->len);
+}
+
+static int papr_vpd_handle_release(struct inode *inode, struct file *file)
+{
+	const struct vpd_blob *blob = file->private_data;
+
+	vpd_blob_free(blob);
+
+	return 0;
+}
+
+static loff_t papr_vpd_handle_seek(struct file *file, loff_t off, int whence)
+{
+	const struct vpd_blob *blob = file->private_data;
+
+	return fixed_size_llseek(file, off, whence, blob->len);
+}
+
+
+static const struct file_operations papr_vpd_handle_ops = {
+	.read = papr_vpd_handle_read,
+	.llseek = papr_vpd_handle_seek,
+	.release = papr_vpd_handle_release,
+};
+
+/**
+ * papr_vpd_create_handle() - Create a fd-based handle for reading VPD.
+ * @ulc: Location code in user memory; defines the scope of the VPD to
+ *       retrieve.
+ *
+ * Handler for PAPR_VPD_IOC_CREATE_HANDLE ioctl command. Validates
+ * @ulc and instantiates an immutable VPD "blob" for it. The blob is
+ * attached to a file descriptor for reading by user space. The memory
+ * backing the blob is freed when the file is released.
+ *
+ * The entire requested VPD is retrieved by this call and all
+ * necessary RTAS interactions are performed before returning the fd
+ * to user space. This keeps the read handler simple and ensures that
+ * the kernel can prevent interleaving of ibm,get-vpd call sequences.
+ *
+ * Return: The installed fd number if successful, -ve errno otherwise.
+ */
+static long papr_vpd_create_handle(struct papr_location_code __user *ulc)
+{
+	struct papr_location_code klc;
+	const struct vpd_blob *blob;
+	struct file *file;
+	long err;
+	int fd;
+
+	if (copy_from_user(&klc, ulc, sizeof(klc)))
+		return -EFAULT;

This is defined in linux/uaccess.h which is not included.

Same for the sysparm driver.

Tested-by: Michal Suchánek <redacted>

+
+	if (!string_is_terminated(klc.str, ARRAY_SIZE(klc.str)))
+		return -EINVAL;
+
+	blob = papr_vpd_retrieve(&klc);
+	if (IS_ERR(blob))
+		return PTR_ERR(blob);
+
+	fd = get_unused_fd_flags(O_RDONLY | O_CLOEXEC);
+	if (fd < 0) {
+		err = fd;
+		goto free_blob;
+	}
+
+	file = anon_inode_getfile("[papr-vpd]", &papr_vpd_handle_ops,
+				  (void *)blob, O_RDONLY);
+	if (IS_ERR(file)) {
+		err = PTR_ERR(file);
+		goto put_fd;
+	}
+
+	file->f_mode |= FMODE_LSEEK | FMODE_PREAD;
+	fd_install(fd, file);
+	return fd;
+put_fd:
+	put_unused_fd(fd);
+free_blob:
+	vpd_blob_free(blob);
+	return err;
+}
+
+/*
+ * Top-level ioctl handler for /dev/papr-vpd.
+ */
+static long papr_vpd_dev_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
+{
+	void __user *argp = (__force void __user *)arg;
+	long ret;
+
+	switch (ioctl) {
+	case PAPR_VPD_IOC_CREATE_HANDLE:
+		ret = papr_vpd_create_handle(argp);
+		break;
+	default:
+		ret = -ENOIOCTLCMD;
+		break;
+	}
+	return ret;
+}
+
+static const struct file_operations papr_vpd_ops = {
+	.unlocked_ioctl = papr_vpd_dev_ioctl,
+};
+
+static struct miscdevice papr_vpd_dev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "papr-vpd",
+	.fops = &papr_vpd_ops,
+};
+
+static __init int papr_vpd_init(void)
+{
+	if (!rtas_function_implemented(RTAS_FN_IBM_GET_VPD))
+		return -ENODEV;
+
+	return misc_register(&papr_vpd_dev);
+}
+machine_device_initcall(pseries, papr_vpd_init);

-- 
2.41.0