diff --git a/.clang-format b/.clang-format
index 10dc5a9a61b3..3f11c8901b43 100644
--- a/.clang-format
+++ b/.clang-format
@@ -109,6 +109,7 @@ ForEachMacros:
   - 'css_for_each_child'
   - 'css_for_each_descendant_post'
   - 'css_for_each_descendant_pre'
+  - 'cxl_for_each_cmd'
   - 'device_for_each_child_node'
   - 'dma_fence_chain_for_each'
   - 'do_for_each_ftrace_op'
diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
index a4c75a28c839..6eb8e634664d 100644
--- a/Documentation/userspace-api/ioctl/ioctl-number.rst
+++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
@@ -352,6 +352,7 @@ Code  Seq#    Include File                                           Comments
                                                                      <mailto:michael.klein@puffin.lb.shuttle.de>
 0xCC  00-0F  drivers/misc/ibmvmc.h                                   pseries VMC driver
 0xCD  01     linux/reiserfs_fs.h
+0xCE  01-02  uapi/linux/cxl_mem.h                                    Compute Express Link Memory Devices
 0xCF  02     fs/cifs/ioctl.c
 0xDB  00-0F  drivers/char/mwave/mwavepub.h
 0xDD  00-3F                                                          ZFCP device driver see drivers/s390/scsi/
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 8bbd2495e237..ce65630bb75e 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
+#include <uapi/linux/cxl_mem.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/cdev.h>
@@ -39,6 +40,7 @@
 #define CXL_MAILBOX_TIMEOUT_MS (2 * HZ)
 
 enum opcode {
+	CXL_MBOX_OP_INVALID		= 0x0000,
 	CXL_MBOX_OP_IDENTIFY		= 0x4000,
 	CXL_MBOX_OP_MAX			= 0x10000
 };
@@ -90,9 +92,57 @@ struct cxl_memdev {
 static int cxl_mem_major;
 static DEFINE_IDA(cxl_memdev_ida);
 
+/**
+ * struct cxl_mem_command - Driver representation of a memory device command
+ * @info: Command information as it exists for the UAPI
+ * @opcode: The actual bits used for the mailbox protocol
+ * @flags: Set of flags reflecting the state of the command.
+ *
+ *  * %CXL_CMD_FLAG_MANDATORY: Hardware must support this command. This flag is
+ *    only used internally by the driver for sanity checking.
+ *
+ * The cxl_mem_command is the driver's internal representation of commands that
+ * are supported by the driver. Some of these commands may not be supported by
+ * the hardware. The driver will use @info to validate the fields passed in by
+ * the user then submit the @opcode to the hardware.
+ *
+ * See struct cxl_command_info.
+ */
+struct cxl_mem_command {
+	struct cxl_command_info info;
+	enum opcode opcode;
+};
+
+#define CXL_CMD(_id, _flags, sin, sout)                                        \
+	[CXL_MEM_COMMAND_ID_##_id] = {                                         \
+	.info =	{                                                              \
+			.id = CXL_MEM_COMMAND_ID_##_id,                        \
+			.flags = CXL_MEM_COMMAND_FLAG_##_flags,                \
+			.size_in = sin,                                        \
+			.size_out = sout,                                      \
+		},                                                             \
+	.opcode = CXL_MBOX_OP_##_id,                                           \
+	}
+
+/*
+ * This table defines the supported mailbox commands for the driver. This table
+ * is made up of a UAPI structure. Non-negative values as parameters in the
+ * table will be validated against the user's input. For example, if size_in is
+ * 0, and the user passed in 1, it is an error.
+ */
+static struct cxl_mem_command mem_commands[] = {
+	CXL_CMD(IDENTIFY, NONE, 0, 0x43),
+};
+
+#define cxl_for_each_cmd(cmd)                                                  \
+	for ((cmd) = &mem_commands[0];                                         \
+	     ((cmd) - mem_commands) < ARRAY_SIZE(mem_commands); (cmd)++)
+
+#define cxl_cmd_count ARRAY_SIZE(mem_commands)
+
 static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
 {
-	const unsigned long start = jiffies;
+	unsigned long start = jiffies;
 	unsigned long end = start;
 
 	while (cxl_doorbell_busy(cxlm)) {
@@ -313,6 +363,243 @@ static void cxl_mem_mbox_put(struct cxl_mem *cxlm)
 	mutex_unlock(&cxlm->mbox_mutex);
 }
 
+/**
+ * handle_mailbox_cmd_from_user() - Dispatch a mailbox command.
+ * @cxlmd: The CXL memory device to communicate with.
+ * @cmd: The validated command.
+ * @in_payload: Pointer to userspace's input payload.
+ * @out_payload: Pointer to userspace's output payload.
+ * @s: The command submitted by userspace. Has output fields.
+ *
+ * Return:
+ *  * %0	- Mailbox transaction succeeded.
+ *  * %-EFAULT	- Something happened with copy_to/from_user.
+ *  * %-ENOMEM  - Couldn't allocate a bounce buffer.
+ *  * %-EINTR	- Mailbox acquisition interrupted.
+ *  * %-E2BIG   - Output payload would overrun user's buffer.
+ *
+ * Creates the appropriate mailbox command on behalf of a userspace request.
+ * Return value, size, and output payload are all copied out to @u. The
+ * parameters for the command must be validated before calling this function.
+ *
+ * A 0 return code indicates the command executed successfully, not that it was
+ * itself successful. IOW, the cmd->retval should always be checked if wanting
+ * to determine the actual result.
+ */
+static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
+					const struct cxl_mem_command *cmd,
+					u64 in_payload, u64 out_payload,
+					struct cxl_send_command __user *s)
+{
+	struct cxl_mem *cxlm = cxlmd->cxlm;
+	struct device *dev = &cxlmd->dev;
+	struct mbox_cmd mbox_cmd = {
+		.opcode = cmd->opcode,
+		.size_in = cmd->info.size_in,
+	};
+	s32 user_size_out;
+	int rc;
+
+	if (get_user(user_size_out, &s->out.size))
+		return -EFAULT;
+
+	if (cmd->info.size_out > 0) /* fixed size command */
+		mbox_cmd.payload_out = kvzalloc(cmd->info.size_out, GFP_KERNEL);
+	else if (cmd->info.size_out < 0) /* variable */
+		mbox_cmd.payload_out = kvzalloc(cxlm->payload_size, GFP_KERNEL);
+
+	if (cmd->info.size_in) {
+		mbox_cmd.payload_in = kvzalloc(cmd->info.size_in, GFP_KERNEL);
+		if (!mbox_cmd.payload_in) {
+			rc = -ENOMEM;
+			goto out;
+		}
+
+		if (copy_from_user(mbox_cmd.payload_in,
+				   u64_to_user_ptr(in_payload),
+				   cmd->info.size_in)) {
+			rc = -EFAULT;
+			goto out;
+		}
+	}
+
+	rc = cxl_mem_mbox_get(cxlm);
+	if (rc)
+		goto out;
+
+	dev_dbg(dev,
+		"Submitting %s command for user\n"
+		"\topcode: %x\n"
+		"\tsize: %ub\n",
+		cxl_command_names[cmd->info.id].name, mbox_cmd.opcode,
+		cmd->info.size_in);
+
+	rc = cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
+	cxl_mem_mbox_put(cxlm);
+	if (rc)
+		goto out;
+
+	rc = put_user(mbox_cmd.return_code, &s->retval);
+	if (rc)
+		goto out;
+
+	if (user_size_out < mbox_cmd.size_out) {
+		rc = -E2BIG;
+		goto out;
+	}
+
+	if (mbox_cmd.size_out) {
+		if (copy_to_user(u64_to_user_ptr(out_payload),
+				 mbox_cmd.payload_out, mbox_cmd.size_out)) {
+			rc = -EFAULT;
+			goto out;
+		}
+	}
+
+	rc = put_user(mbox_cmd.size_out, &s->out.size);
+
+out:
+	kvfree(mbox_cmd.payload_in);
+	kvfree(mbox_cmd.payload_out);
+	return rc;
+}
+
+/**
+ * cxl_validate_cmd_from_user() - Check fields for CXL_MEM_SEND_COMMAND.
+ * @cxlm: &struct cxl_mem device whose mailbox will be used.
+ * @send_cmd: &struct cxl_send_command copied in from userspace.
+ * @out_cmd: Sanitized and populated &struct cxl_mem_command.
+ *
+ * Return:
+ *  * %0	- @out_cmd is ready to send.
+ *  * %-ENOTTY	- Invalid command specified.
+ *  * %-EINVAL	- Reserved fields or invalid values were used.
+ *  * %-EPERM	- Attempted to use a protected command.
+ *  * %-ENOMEM	- Input or output buffer wasn't sized properly.
+ *
+ * The result of this command is a fully validated command in @out_cmd that is
+ * safe to send to the hardware.
+ *
+ * See handle_mailbox_cmd_from_user()
+ */
+static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
+				      const struct cxl_send_command *send_cmd,
+				      struct cxl_mem_command *out_cmd)
+{
+	const struct cxl_command_info *info;
+	struct cxl_mem_command *c;
+
+	if (send_cmd->id == 0 || send_cmd->id >= CXL_MEM_COMMAND_ID_MAX)
+		return -ENOTTY;
+
+	/*
+	 * The user can never specify an input payload larger than
+	 * hardware supports, but output can be arbitrarily large,
+	 * simply write out as much data as the hardware provides.
+	 */
+	if (send_cmd->in.size > cxlm->payload_size)
+		return -EINVAL;
+
+	if (send_cmd->flags & ~CXL_MEM_COMMAND_FLAG_MASK)
+		return -EINVAL;
+
+	if (send_cmd->rsvd)
+		return -EINVAL;
+
+	if (send_cmd->in.rsvd || send_cmd->out.rsvd)
+		return -EINVAL;
+
+	/* Convert user's command into the internal representation */
+	c = &mem_commands[send_cmd->id];
+	info = &c->info;
+
+	if (info->flags & CXL_MEM_COMMAND_FLAG_KERNEL)
+		return -EPERM;
+
+	/* Check the input buffer is the expected size */
+	if (info->size_in >= 0 && info->size_in != send_cmd->in.size)
+		return -ENOMEM;
+
+	/* Check the output buffer is at least large enough */
+	if (info->size_out >= 0 && send_cmd->out.size < info->size_out)
+		return -ENOMEM;
+
+	/* Setting a few const fields here... */
+	memcpy(out_cmd, c, sizeof(*c));
+	out_cmd->info.size_in = send_cmd->in.size;
+	out_cmd->info.size_out = send_cmd->out.size;
+
+	return 0;
+}
+
+static int cxl_query_cmd(struct cxl_memdev *cxlmd,
+			 struct cxl_mem_query_commands __user *q)
+{
+	struct device *dev = &cxlmd->dev;
+	struct cxl_mem_command *cmd;
+	u32 n_commands;
+	int j = 0;
+
+	dev_dbg(dev, "Query IOCTL\n");
+
+	if (get_user(n_commands, &q->n_commands))
+		return -EFAULT;
+
+	/* returns the total number if 0 elements are requested. */
+	if (n_commands == 0)
+		return put_user(cxl_cmd_count, &q->n_commands);
+
+	/*
+	 * otherwise, return max(n_commands, total commands) cxl_command_info
+	 * structures.
+	 */
+	cxl_for_each_cmd(cmd) {
+		const struct cxl_command_info *info = &cmd->info;
+
+		if (copy_to_user(&q->commands[j++], info, sizeof(*info)))
+			return -EFAULT;
+
+		if (j == n_commands)
+			break;
+	}
+
+	return 0;
+}
+
+static int cxl_send_cmd(struct cxl_memdev *cxlmd,
+			struct cxl_send_command __user *s)
+{
+	struct device *dev = &cxlmd->dev;
+	struct cxl_send_command send;
+	struct cxl_mem_command c;
+	int rc;
+
+	dev_dbg(dev, "Send IOCTL\n");
+
+	if (copy_from_user(&send, s, sizeof(send)))
+		return -EFAULT;
+
+	rc = cxl_validate_cmd_from_user(cxlmd->cxlm, &send, &c);
+	if (rc)
+		return rc;
+
+	return handle_mailbox_cmd_from_user(cxlmd, &c, send.in.payload,
+					    send.out.payload, s);
+}
+
+static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd,
+			       unsigned long arg)
+{
+	switch (cmd) {
+	case CXL_MEM_QUERY_COMMANDS:
+		return cxl_query_cmd(cxlmd, (void __user *)arg);
+	case CXL_MEM_SEND_COMMAND:
+		return cxl_send_cmd(cxlmd, (void __user *)arg);
+	default:
+		return -ENOTTY;
+	}
+}
+
 static long cxl_memdev_ioctl(struct file *file, unsigned int cmd,
 			     unsigned long arg)
 {
@@ -326,7 +613,7 @@ static long cxl_memdev_ioctl(struct file *file, unsigned int cmd,
 	if (!percpu_ref_tryget_live(&cxlmd->ops_active))
 		return -ENXIO;
 
-	/* TODO: ioctl body */
+	rc = __cxl_memdev_ioctl(cxlmd, cmd, arg);
 
 	percpu_ref_put(&cxlmd->ops_active);
 
diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
new file mode 100644
index 000000000000..f1f7e9f32ea5
--- /dev/null
+++ b/include/uapi/linux/cxl_mem.h
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * CXL IOCTLs for Memory Devices
+ */
+
+#ifndef _UAPI_CXL_MEM_H_
+#define _UAPI_CXL_MEM_H_
+
+#include <linux/types.h>
+
+/**
+ * DOC: UAPI
+ *
+ * Not all of all commands that the driver supports are always available for use
+ * by userspace. Userspace must check the results from the QUERY command in
+ * order to determine the live set of commands.
+ */
+
+#define CXL_MEM_QUERY_COMMANDS _IOR(0xCE, 1, struct cxl_mem_query_commands)
+#define CXL_MEM_SEND_COMMAND _IOWR(0xCE, 2, struct cxl_send_command)
+
+#define CXL_CMDS                                                          \
+	___C(INVALID, "Invalid Command"),                                 \
+	___C(IDENTIFY, "Identify Command"),                               \
+	___C(MAX, "Last command")
+
+#define ___C(a, b) CXL_MEM_COMMAND_ID_##a
+enum { CXL_CMDS };
+
+#undef ___C
+#define ___C(a, b) { b }
+static const struct {
+	const char *name;
+} cxl_command_names[] = { CXL_CMDS };
+#undef ___C
+
+/**
+ * struct cxl_command_info - Command information returned from a query.
+ * @id: ID number for the command.
+ * @flags: Flags that specify command behavior.
+ *
+ *  * %CXL_MEM_COMMAND_FLAG_KERNEL: This command is reserved for exclusive
+ *    kernel use.
+ *  * %CXL_MEM_COMMAND_FLAG_MUTEX: This command may require coordination with
+ *    the kernel in order to complete successfully.
+ *
+ * @size_in: Expected input size, or -1 if variable length.
+ * @size_out: Expected output size, or -1 if variable length.
+ *
+ * Represents a single command that is supported by both the driver and the
+ * hardware. This is returned as part of an array from the query ioctl. The
+ * following would be a command named "foobar" that takes a variable length
+ * input and returns 0 bytes of output.
+ *
+ *  - @id = 10
+ *  - @flags = CXL_MEM_COMMAND_FLAG_MUTEX
+ *  - @size_in = -1
+ *  - @size_out = 0
+ *
+ * See struct cxl_mem_query_commands.
+ */
+struct cxl_command_info {
+	__u32 id;
+
+	__u32 flags;
+#define CXL_MEM_COMMAND_FLAG_NONE 0
+#define CXL_MEM_COMMAND_FLAG_KERNEL BIT(0)
+#define CXL_MEM_COMMAND_FLAG_MASK GENMASK(1, 0)
+
+	__s32 size_in;
+	__s32 size_out;
+};
+
+/**
+ * struct cxl_mem_query_commands - Query supported commands.
+ * @n_commands: In/out parameter. When @n_commands is > 0, the driver will
+ *		return min(num_support_commands, n_commands). When @n_commands
+ *		is 0, driver will return the number of total supported commands.
+ * @rsvd: Reserved for future use.
+ * @commands: Output array of supported commands. This array must be allocated
+ *            by userspace to be at least min(num_support_commands, @n_commands)
+ *
+ * Allow userspace to query the available commands supported by both the driver,
+ * and the hardware. Commands that aren't supported by either the driver, or the
+ * hardware are not returned in the query.
+ *
+ * Examples:
+ *
+ *  - { .n_commands = 0 } // Get number of supported commands
+ *  - { .n_commands = 15, .commands = buf } // Return first 15 (or less)
+ *    supported commands
+ *
+ *  See struct cxl_command_info.
+ */
+struct cxl_mem_query_commands {
+	/*
+	 * Input: Number of commands to return (space allocated by user)
+	 * Output: Number of commands supported by the driver/hardware
+	 *
+	 * If n_commands is 0, kernel will only return number of commands and
+	 * not try to populate commands[], thus allowing userspace to know how
+	 * much space to allocate
+	 */
+	__u32 n_commands;
+	__u32 rsvd;
+
+	struct cxl_command_info __user commands[]; /* out: supported commands */
+};
+
+/**
+ * struct cxl_send_command - Send a command to a memory device.
+ * @id: The command to send to the memory device. This must be one of the
+ *	commands returned by the query command.
+ * @flags: Flags for the command (input).
+ * @rsvd: Must be zero.
+ * @retval: Return value from the memory device (output).
+ * @in.size: Size of the payload to provide to the device (input).
+ * @in.rsvd: Must be zero.
+ * @in.payload: Pointer to memory for payload input (little endian order).
+ * @out.size: Size of the payload received from the device (input/output). This
+ *	      field is filled in by userspace to let the driver know how much
+ *	      space was allocated for output. It is populated by the driver to
+ *	      let userspace know how large the output payload actually was.
+ * @out.rsvd: Must be zero.
+ * @out.payload: Pointer to memory for payload output (little endian order).
+ *
+ * Mechanism for userspace to send a command to the hardware for processing. The
+ * driver will do basic validation on the command sizes. In some cases even the
+ * payload may be introspected. Userspace is required to allocate large
+ * enough buffers for size_out which can be variable length in certain
+ * situations.
+ */
+struct cxl_send_command {
+	__u32 id;
+	__u32 flags;
+	__u32 rsvd;
+	__u32 retval;
+
+	struct {
+		__s32 size;
+		__u32 rsvd;
+		__u64 payload;
+	} in;
+
+	struct {
+		__s32 size;
+		__u32 rsvd;
+		__u64 payload;
+	} out;
+};
+
+#endif
