cxl/mem: Add basic IOCTL interface

Add a straightforward IOCTL that provides a mechanism for userspace to
query the supported memory device commands. CXL commands as they appear
to userspace are described as part of the UAPI kerneldoc. The command
list returned via this IOCTL will contain the full set of commands that
the driver supports, however, some of those commands may not be
available for use by userspace.

Memory device commands first appear in the CXL 2.0 specification. They
are submitted through a mailbox mechanism specified in the CXL 2.0
specification.

The send command allows userspace to issue mailbox commands directly to
the hardware. The list of available commands to send are the output of
the query command. The driver verifies basic properties of the command
and possibly inspect the input (or output) payload to determine whether
or not the command is allowed (or might taint the kernel).

Reported-by: kernel test robot <lkp@intel.com> # bug in earlier revision
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com> (v2)
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20210217040958.1354670-5-ben.widawsky@intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 156 insertions, 0 deletions

diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
new file mode 100644
index 000000000000..887781dc3b6c
--- /dev/null
+++ b/include/uapi/linux/cxl_mem.h
@@ -0,0 +1,156 @@
+/* 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, "invalid / 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 };
+
+/*
+ * Here's how this actually breaks out:
+ * cxl_command_names[] = {
+ *	[CXL_MEM_COMMAND_ID_INVALID] = { "Invalid Command" },
+ *	[CXL_MEM_COMMAND_ID_IDENTIFY] = { "Identify Command" },
+ *	...
+ *	[CXL_MEM_COMMAND_ID_MAX] = { "invalid / last command" },
+ * };
+ */
+
+#undef ___C
+
+/**
+ * struct cxl_command_info - Command information returned from a query.
+ * @id: ID number for the command.
+ * @flags: Flags that specify command behavior.
+ * @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 that takes a variable length input and returns 0
+ * bytes of output.
+ *
+ *  - @id = 10
+ *  - @flags = 0
+ *  - @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_MASK GENMASK(0, 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: Parameters associated with input payload.
+ * @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, payload is little endian.
+ * @out: Parameters associated with output payload.
+ * @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, payload is little endian.
+ *
+ * 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