s390/cpumf: Add support for complete counter set extraction

Add support to the CPU Measurement counter facility device driver
to extract complete counter sets per CPU and per counter set from user
space. This includes a new device named /dev/hwctr and support
for the device driver functions open, close and ioctl. Other
functions are not supported.

The ioctl command supports 3 subcommands:
S390_HWCTR_START: enables counter sets on a list of CPUs.
S390_HWCTR_STOP: disables counter sets on a list of CPUs.
S390_HWCTR_READ: reads counter sets on a list of CPUs.

The ioctl(..., S390_HWCTR_READ, ...) is the only subcommand which
returns data.  It requires member data_bytes to be positive and
indicates the maximum amount of data available to store counter set
data. The other ioctl() subcommands do not use this member and it
should be set to zero.
The S390_HWCTR_READ subcommand returns the following data:

The cpuset data is flattened using the following scheme, stored in member
data:

 0x0       0x8   0xc       0x10  0x10      0x18  0x20  0x28         0xU-1
 +---------+-----+---------+-----+---------+-----+-----+------+------+
 | no_cpus | cpu | no_sets | set | no_cnts | cv1 | cv2 | .... | cv_n |
 +---------+-----+---------+-----+---------+-----+-----+------+------+

                           0xU   0xU+4     0xU+8 0xU+10             0xV-1
                           +-----+---------+-----+-----+------+------+
                           | set | no_cnts | cv1 | cv2 | .... | cv_n |
                           +-----+---------+-----+-----+------+------+

           0xV   0xV+4     0xV+8 0xV+c
           +-----+---------+-----+---------+-----+-----+------+------+
           | cpu | no_sets | set | no_cnts | cv1 | cv2 | .... | cv_n |
           +-----+---------+-----+---------+-----+-----+------+------+

U and V denote arbitrary hexadezimal addresses.
The first integer represents the number of CPUs data was extracted
from. This is followed by CPU number and number of counter sets extracted.
Both are two integer values. This is followed by the set identifer
and number of counters extracted. Both are two integer values. This is
followed by the counter values, each element is eight bytes in size.

The S390_HWCTR_READ ioctl subcommand is also limited to one call per
minute. This ensures that an application does not read out the
counter sets too often and reduces the overall CPU performance.
The complete counter set extraction is an expensive operation.

Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/uapi/asm/perf_cpum_cf_diag.h

@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright IBM Corp. 2021
+ * Interface implementation for communication with the CPU Measurement
+ * counter facility device driver.
+ *
+ * Author(s): Thomas Richter <tmricht@linux.ibm.com>
+ *
+ * Define for ioctl() commands to communicate with the CPU Measurement
+ * counter facility device driver.
+ */
+
+#ifndef _PERF_CPUM_CF_DIAG_H
+#define _PERF_CPUM_CF_DIAG_H
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+#define S390_HWCTR_DEVICE		"hwctr"
+#define S390_HWCTR_START_VERSION	1
+
+struct s390_ctrset_start {		/* Set CPUs to operate on */
+	__u64 version;			/* Version of interface */
+	__u64 data_bytes;		/* # of bytes required */
+	__u64 cpumask_len;		/* Length of CPU mask in bytes */
+	__u64 *cpumask;			/* Pointer to CPU mask */
+	__u64 counter_sets;		/* Bit mask of counter sets to get */
+};
+
+struct s390_ctrset_setdata {		/* Counter set data */
+	__u32 set;			/* Counter set number */
+	__u32 no_cnts;			/* # of counters stored in cv[] */
+	__u64 cv[0];			/* Counter values (variable length) */
+};
+
+struct s390_ctrset_cpudata {		/* Counter set data per CPU */
+	__u32 cpu_nr;			/* CPU number */
+	__u32 no_sets;			/* # of counters sets in data[] */
+	struct s390_ctrset_setdata data[0];
+};
+
+struct s390_ctrset_read {		/* Structure to get all ctr sets */
+	__u64 no_cpus;			/* Total # of CPUs data taken from */
+	struct s390_ctrset_cpudata data[0];
+};
+
+#define S390_HWCTR_MAGIC	'C'	/* Random magic # for ioctls */
+#define	S390_HWCTR_START	_IOWR(S390_HWCTR_MAGIC, 1, struct s390_ctrset_start)
+#define	S390_HWCTR_STOP		_IO(S390_HWCTR_MAGIC, 2)
+#define	S390_HWCTR_READ		_IOWR(S390_HWCTR_MAGIC, 3, struct s390_ctrset_read)
+#endif