LoongArch: Add perf events support

The perf events infrastructure of LoongArch is very similar to old MIPS-
based Loongson, so most of the codes are derived from MIPS.

Signed-off-by: Huacai Chen <[e-mail]>

arch/loongarch/Kconfig

···
 	select HAVE_NMI
 	select HAVE_PCI
 	select HAVE_PERF_EVENTS
+	select HAVE_PERF_REGS
+	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
 	select HAVE_SETUP_PER_CPU_AREA if NUMA

arch/loongarch/include/asm/perf_event.h

···
 
 #ifndef __LOONGARCH_PERF_EVENT_H__
 #define __LOONGARCH_PERF_EVENT_H__
-/* Nothing to show here; the file is required by linux/perf_event.h. */
+
+#define perf_arch_bpf_user_pt_regs(regs) (struct user_pt_regs *)regs
+
 #endif /* __LOONGARCH_PERF_EVENT_H__ */

arch/loongarch/include/uapi/asm/perf_regs.h

···
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _ASM_LOONGARCH_PERF_REGS_H
+#define _ASM_LOONGARCH_PERF_REGS_H
+
+enum perf_event_loongarch_regs {
+	PERF_REG_LOONGARCH_PC,
+	PERF_REG_LOONGARCH_R1,
+	PERF_REG_LOONGARCH_R2,
+	PERF_REG_LOONGARCH_R3,
+	PERF_REG_LOONGARCH_R4,
+	PERF_REG_LOONGARCH_R5,
+	PERF_REG_LOONGARCH_R6,
+	PERF_REG_LOONGARCH_R7,
+	PERF_REG_LOONGARCH_R8,
+	PERF_REG_LOONGARCH_R9,
+	PERF_REG_LOONGARCH_R10,
+	PERF_REG_LOONGARCH_R11,
+	PERF_REG_LOONGARCH_R12,
+	PERF_REG_LOONGARCH_R13,
+	PERF_REG_LOONGARCH_R14,
+	PERF_REG_LOONGARCH_R15,
+	PERF_REG_LOONGARCH_R16,
+	PERF_REG_LOONGARCH_R17,
+	PERF_REG_LOONGARCH_R18,
+	PERF_REG_LOONGARCH_R19,
+	PERF_REG_LOONGARCH_R20,
+	PERF_REG_LOONGARCH_R21,
+	PERF_REG_LOONGARCH_R22,
+	PERF_REG_LOONGARCH_R23,
+	PERF_REG_LOONGARCH_R24,
+	PERF_REG_LOONGARCH_R25,
+	PERF_REG_LOONGARCH_R26,
+	PERF_REG_LOONGARCH_R27,
+	PERF_REG_LOONGARCH_R28,
+	PERF_REG_LOONGARCH_R29,
+	PERF_REG_LOONGARCH_R30,
+	PERF_REG_LOONGARCH_R31,
+	PERF_REG_LOONGARCH_MAX,
+};
+#endif /* _ASM_LOONGARCH_PERF_REGS_H */

arch/loongarch/kernel/Makefile

···
 obj-$(CONFIG_UNWINDER_GUESS)	+= unwind_guess.o
 obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
 
+obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o perf_regs.o
+
 CPPFLAGS_vmlinux.lds		:= $(KBUILD_CFLAGS)

arch/loongarch/kernel/perf_event.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Linux performance counter support for LoongArch.
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 2010 MIPS Technologies, Inc.
+ * Copyright (C) 2011 Cavium Networks, Inc.
+ * Author: Deng-Cheng Zhu
+ */
+
+#include <linux/cpumask.h>
+#include <linux/interrupt.h>
+#include <linux/smp.h>
+#include <linux/kernel.h>
+#include <linux/perf_event.h>
+#include <linux/uaccess.h>
+#include <linux/sched/task_stack.h>
+
+#include <asm/irq.h>
+#include <asm/irq_regs.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+/*
+ * Get the return address for a single stackframe and return a pointer to the
+ * next frame tail.
+ */
+static unsigned long
+user_backtrace(struct perf_callchain_entry_ctx *entry, unsigned long fp)
+{
+	unsigned long err;
+	unsigned long __user *user_frame_tail;
+	struct stack_frame buftail;
+
+	user_frame_tail = (unsigned long __user *)(fp - sizeof(struct stack_frame));
+
+	/* Also check accessibility of one struct frame_tail beyond */
+	if (!access_ok(user_frame_tail, sizeof(buftail)))
+		return 0;
+
+	pagefault_disable();
+	err = __copy_from_user_inatomic(&buftail, user_frame_tail, sizeof(buftail));
+	pagefault_enable();
+
+	if (err || (unsigned long)user_frame_tail >= buftail.fp)
+		return 0;
+
+	perf_callchain_store(entry, buftail.ra);
+
+	return buftail.fp;
+}
+
+void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
+			 struct pt_regs *regs)
+{
+	unsigned long fp;
+
+	if (perf_guest_state()) {
+		/* We don't support guest os callchain now */
+		return;
+	}
+
+	perf_callchain_store(entry, regs->csr_era);
+
+	fp = regs->regs[22];
+
+	while (entry->nr < entry->max_stack && fp && !((unsigned long)fp & 0xf))
+		fp = user_backtrace(entry, fp);
+}
+
+void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
+			   struct pt_regs *regs)
+{
+	struct unwind_state state;
+	unsigned long addr;
+
+	for (unwind_start(&state, current, regs);
+	      !unwind_done(&state); unwind_next_frame(&state)) {
+		addr = unwind_get_return_address(&state);
+		if (!addr || perf_callchain_store(entry, addr))
+			return;
+	}
+}
+
+#define LOONGARCH_MAX_HWEVENTS 32
+
+struct cpu_hw_events {
+	/* Array of events on this cpu. */
+	struct perf_event	*events[LOONGARCH_MAX_HWEVENTS];
+
+	/*
+	 * Set the bit (indexed by the counter number) when the counter
+	 * is used for an event.
+	 */
+	unsigned long		used_mask[BITS_TO_LONGS(LOONGARCH_MAX_HWEVENTS)];
+
+	/*
+	 * Software copy of the control register for each performance counter.
+	 */
+	unsigned int		saved_ctrl[LOONGARCH_MAX_HWEVENTS];
+};
+static DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
+	.saved_ctrl = {0},
+};
+
+/* The description of LoongArch performance events. */
+struct loongarch_perf_event {
+	unsigned int event_id;
+};
+
+static struct loongarch_perf_event raw_event;
+static DEFINE_MUTEX(raw_event_mutex);
+
+#define C(x) PERF_COUNT_HW_CACHE_##x
+#define HW_OP_UNSUPPORTED		0xffffffff
+#define CACHE_OP_UNSUPPORTED		0xffffffff
+
+#define PERF_MAP_ALL_UNSUPPORTED					\
+	[0 ... PERF_COUNT_HW_MAX - 1] = {HW_OP_UNSUPPORTED}
+
+#define PERF_CACHE_MAP_ALL_UNSUPPORTED					\
+[0 ... C(MAX) - 1] = {							\
+	[0 ... C(OP_MAX) - 1] = {					\
+		[0 ... C(RESULT_MAX) - 1] = {CACHE_OP_UNSUPPORTED},	\
+	},								\
+}
+
+struct loongarch_pmu {
+	u64		max_period;
+	u64		valid_count;
+	u64		overflow;
+	const char	*name;
+	unsigned int	num_counters;
+	u64		(*read_counter)(unsigned int idx);
+	void		(*write_counter)(unsigned int idx, u64 val);
+	const struct loongarch_perf_event *(*map_raw_event)(u64 config);
+	const struct loongarch_perf_event (*general_event_map)[PERF_COUNT_HW_MAX];
+	const struct loongarch_perf_event (*cache_event_map)
+				[PERF_COUNT_HW_CACHE_MAX]
+				[PERF_COUNT_HW_CACHE_OP_MAX]
+				[PERF_COUNT_HW_CACHE_RESULT_MAX];
+};
+
+static struct loongarch_pmu loongarch_pmu;
+
+#define M_PERFCTL_EVENT(event)	(event & CSR_PERFCTRL_EVENT)
+
+#define M_PERFCTL_COUNT_EVENT_WHENEVER	(CSR_PERFCTRL_PLV0 |	\
+					CSR_PERFCTRL_PLV1 |	\
+					CSR_PERFCTRL_PLV2 |	\
+					CSR_PERFCTRL_PLV3 |	\
+					CSR_PERFCTRL_IE)
+
+#define M_PERFCTL_CONFIG_MASK		0x1f0000
+
+static void pause_local_counters(void);
+static void resume_local_counters(void);
+
+static u64 loongarch_pmu_read_counter(unsigned int idx)
+{
+	u64 val = -1;
+
+	switch (idx) {
+	case 0:
+		val = read_csr_perfcntr0();
+		break;
+	case 1:
+		val = read_csr_perfcntr1();
+		break;
+	case 2:
+		val = read_csr_perfcntr2();
+		break;
+	case 3:
+		val = read_csr_perfcntr3();
+		break;
+	default:
+		WARN_ONCE(1, "Invalid performance counter number (%d)\n", idx);
+		return 0;
+	}
+
+	return val;
+}
+
+static void loongarch_pmu_write_counter(unsigned int idx, u64 val)
+{
+	switch (idx) {
+	case 0:
+		write_csr_perfcntr0(val);
+		return;
+	case 1:
+		write_csr_perfcntr1(val);
+		return;
+	case 2:
+		write_csr_perfcntr2(val);
+		return;
+	case 3:
+		write_csr_perfcntr3(val);
+		return;
+	default:
+		WARN_ONCE(1, "Invalid performance counter number (%d)\n", idx);
+		return;
+	}
+}
+
+static unsigned int loongarch_pmu_read_control(unsigned int idx)
+{
+	unsigned int val = -1;
+
+	switch (idx) {
+	case 0:
+		val = read_csr_perfctrl0();
+		break;
+	case 1:
+		val = read_csr_perfctrl1();
+		break;
+	case 2:
+		val = read_csr_perfctrl2();
+		break;
+	case 3:
+		val = read_csr_perfctrl3();
+		break;
+	default:
+		WARN_ONCE(1, "Invalid performance counter number (%d)\n", idx);
+		return 0;
+	}
+
+	return val;
+}
+
+static void loongarch_pmu_write_control(unsigned int idx, unsigned int val)
+{
+	switch (idx) {
+	case 0:
+		write_csr_perfctrl0(val);
+		return;
+	case 1:
+		write_csr_perfctrl1(val);
+		return;
+	case 2:
+		write_csr_perfctrl2(val);
+		return;
+	case 3:
+		write_csr_perfctrl3(val);
+		return;
+	default:
+		WARN_ONCE(1, "Invalid performance counter number (%d)\n", idx);
+		return;
+	}
+}
+
+static int loongarch_pmu_alloc_counter(struct cpu_hw_events *cpuc, struct hw_perf_event *hwc)
+{
+	int i;
+
+	for (i = 0; i < loongarch_pmu.num_counters; i++) {
+		if (!test_and_set_bit(i, cpuc->used_mask))
+			return i;
+	}
+
+	return -EAGAIN;
+}
+
+static void loongarch_pmu_enable_event(struct hw_perf_event *evt, int idx)
+{
+	unsigned int cpu;
+	struct perf_event *event = container_of(evt, struct perf_event, hw);
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	WARN_ON(idx < 0 || idx >= loongarch_pmu.num_counters);
+
+	/* Make sure interrupt enabled. */
+	cpuc->saved_ctrl[idx] = M_PERFCTL_EVENT(evt->event_base & 0xff) |
+		(evt->config_base & M_PERFCTL_CONFIG_MASK) | CSR_PERFCTRL_IE;
+
+	cpu = (event->cpu >= 0) ? event->cpu : smp_processor_id();
+
+	/*
+	 * We do not actually let the counter run. Leave it until start().
+	 */
+	pr_debug("Enabling perf counter for CPU%d\n", cpu);
+}
+
+static void loongarch_pmu_disable_event(int idx)
+{
+	unsigned long flags;
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	WARN_ON(idx < 0 || idx >= loongarch_pmu.num_counters);
+
+	local_irq_save(flags);
+	cpuc->saved_ctrl[idx] = loongarch_pmu_read_control(idx) &
+		~M_PERFCTL_COUNT_EVENT_WHENEVER;
+	loongarch_pmu_write_control(idx, cpuc->saved_ctrl[idx]);
+	local_irq_restore(flags);
+}
+
+static int loongarch_pmu_event_set_period(struct perf_event *event,
+				    struct hw_perf_event *hwc,
+				    int idx)
+{
+	int ret = 0;
+	u64 left = local64_read(&hwc->period_left);
+	u64 period = hwc->sample_period;
+
+	if (unlikely((left + period) & (1ULL << 63))) {
+		/* left underflowed by more than period. */
+		left = period;
+		local64_set(&hwc->period_left, left);
+		hwc->last_period = period;
+		ret = 1;
+	} else	if (unlikely((left + period) <= period)) {
+		/* left underflowed by less than period. */
+		left += period;
+		local64_set(&hwc->period_left, left);
+		hwc->last_period = period;
+		ret = 1;
+	}
+
+	if (left > loongarch_pmu.max_period) {
+		left = loongarch_pmu.max_period;
+		local64_set(&hwc->period_left, left);
+	}
+
+	local64_set(&hwc->prev_count, loongarch_pmu.overflow - left);
+
+	loongarch_pmu.write_counter(idx, loongarch_pmu.overflow - left);
+
+	perf_event_update_userpage(event);
+
+	return ret;
+}
+
+static void loongarch_pmu_event_update(struct perf_event *event,
+				 struct hw_perf_event *hwc,
+				 int idx)
+{
+	u64 delta;
+	u64 prev_raw_count, new_raw_count;
+
+again:
+	prev_raw_count = local64_read(&hwc->prev_count);
+	new_raw_count = loongarch_pmu.read_counter(idx);
+
+	if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
+				new_raw_count) != prev_raw_count)
+		goto again;
+
+	delta = new_raw_count - prev_raw_count;
+
+	local64_add(delta, &event->count);
+	local64_sub(delta, &hwc->period_left);
+}
+
+static void loongarch_pmu_start(struct perf_event *event, int flags)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	if (flags & PERF_EF_RELOAD)
+		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
+
+	hwc->state = 0;
+
+	/* Set the period for the event. */
+	loongarch_pmu_event_set_period(event, hwc, hwc->idx);
+
+	/* Enable the event. */
+	loongarch_pmu_enable_event(hwc, hwc->idx);
+}
+
+static void loongarch_pmu_stop(struct perf_event *event, int flags)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	if (!(hwc->state & PERF_HES_STOPPED)) {
+		/* We are working on a local event. */
+		loongarch_pmu_disable_event(hwc->idx);
+		barrier();
+		loongarch_pmu_event_update(event, hwc, hwc->idx);
+		hwc->state |= PERF_HES_STOPPED | PERF_HES_UPTODATE;
+	}
+}
+
+static int loongarch_pmu_add(struct perf_event *event, int flags)
+{
+	int idx, err = 0;
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct hw_perf_event *hwc = &event->hw;
+
+	perf_pmu_disable(event->pmu);
+
+	/* To look for a free counter for this event. */
+	idx = loongarch_pmu_alloc_counter(cpuc, hwc);
+	if (idx < 0) {
+		err = idx;
+		goto out;
+	}
+
+	/*
+	 * If there is an event in the counter we are going to use then
+	 * make sure it is disabled.
+	 */
+	event->hw.idx = idx;
+	loongarch_pmu_disable_event(idx);
+	cpuc->events[idx] = event;
+
+	hwc->state = PERF_HES_STOPPED | PERF_HES_UPTODATE;
+	if (flags & PERF_EF_START)
+		loongarch_pmu_start(event, PERF_EF_RELOAD);
+
+	/* Propagate our changes to the userspace mapping. */
+	perf_event_update_userpage(event);
+
+out:
+	perf_pmu_enable(event->pmu);
+	return err;
+}
+
+static void loongarch_pmu_del(struct perf_event *event, int flags)
+{
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+	struct hw_perf_event *hwc = &event->hw;
+	int idx = hwc->idx;
+
+	WARN_ON(idx < 0 || idx >= loongarch_pmu.num_counters);
+
+	loongarch_pmu_stop(event, PERF_EF_UPDATE);
+	cpuc->events[idx] = NULL;
+	clear_bit(idx, cpuc->used_mask);
+
+	perf_event_update_userpage(event);
+}
+
+static void loongarch_pmu_read(struct perf_event *event)
+{
+	struct hw_perf_event *hwc = &event->hw;
+
+	/* Don't read disabled counters! */
+	if (hwc->idx < 0)
+		return;
+
+	loongarch_pmu_event_update(event, hwc, hwc->idx);
+}
+
+static void loongarch_pmu_enable(struct pmu *pmu)
+{
+	resume_local_counters();
+}
+
+static void loongarch_pmu_disable(struct pmu *pmu)
+{
+	pause_local_counters();
+}
+
+static DEFINE_MUTEX(pmu_reserve_mutex);
+static atomic_t active_events = ATOMIC_INIT(0);
+
+static int get_pmc_irq(void)
+{
+	struct irq_domain *d = irq_find_matching_fwnode(cpuintc_handle, DOMAIN_BUS_ANY);
+
+	if (d)
+		return irq_create_mapping(d, EXCCODE_PMC - EXCCODE_INT_START);
+
+	return -EINVAL;
+}
+
+static void reset_counters(void *arg);
+static int __hw_perf_event_init(struct perf_event *event);
+
+static void hw_perf_event_destroy(struct perf_event *event)
+{
+	if (atomic_dec_and_mutex_lock(&active_events, &pmu_reserve_mutex)) {
+		on_each_cpu(reset_counters, NULL, 1);
+		free_irq(get_pmc_irq(), &loongarch_pmu);
+		mutex_unlock(&pmu_reserve_mutex);
+	}
+}
+
+static void handle_associated_event(struct cpu_hw_events *cpuc, int idx,
+			struct perf_sample_data *data, struct pt_regs *regs)
+{
+	struct perf_event *event = cpuc->events[idx];
+	struct hw_perf_event *hwc = &event->hw;
+
+	loongarch_pmu_event_update(event, hwc, idx);
+	data->period = event->hw.last_period;
+	if (!loongarch_pmu_event_set_period(event, hwc, idx))
+		return;
+
+	if (perf_event_overflow(event, data, regs))
+		loongarch_pmu_disable_event(idx);
+}
+
+static irqreturn_t pmu_handle_irq(int irq, void *dev)
+{
+	int n;
+	int handled = IRQ_NONE;
+	uint64_t counter;
+	struct pt_regs *regs;
+	struct perf_sample_data data;
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	/*
+	 * First we pause the local counters, so that when we are locked
+	 * here, the counters are all paused. When it gets locked due to
+	 * perf_disable(), the timer interrupt handler will be delayed.
+	 *
+	 * See also loongarch_pmu_start().
+	 */
+	pause_local_counters();
+
+	regs = get_irq_regs();
+
+	perf_sample_data_init(&data, 0, 0);
+
+	for (n = 0; n < loongarch_pmu.num_counters; n++) {
+		if (test_bit(n, cpuc->used_mask)) {
+			counter = loongarch_pmu.read_counter(n);
+			if (counter & loongarch_pmu.overflow) {
+				handle_associated_event(cpuc, n, &data, regs);
+				handled = IRQ_HANDLED;
+			}
+		}
+	}
+
+	resume_local_counters();
+
+	/*
+	 * Do all the work for the pending perf events. We can do this
+	 * in here because the performance counter interrupt is a regular
+	 * interrupt, not NMI.
+	 */
+	if (handled == IRQ_HANDLED)
+		irq_work_run();
+
+	return handled;
+}
+
+static int loongarch_pmu_event_init(struct perf_event *event)
+{
+	int r, irq;
+	unsigned long flags;
+
+	/* does not support taken branch sampling */
+	if (has_branch_stack(event))
+		return -EOPNOTSUPP;
+
+	switch (event->attr.type) {
+	case PERF_TYPE_RAW:
+	case PERF_TYPE_HARDWARE:
+	case PERF_TYPE_HW_CACHE:
+		break;
+
+	default:
+		/* Init it to avoid false validate_group */
+		event->hw.event_base = 0xffffffff;
+		return -ENOENT;
+	}
+
+	if (event->cpu >= 0 && !cpu_online(event->cpu))
+		return -ENODEV;
+
+	irq = get_pmc_irq();
+	flags = IRQF_PERCPU | IRQF_NOBALANCING | IRQF_NO_THREAD | IRQF_NO_SUSPEND | IRQF_SHARED;
+	if (!atomic_inc_not_zero(&active_events)) {
+		mutex_lock(&pmu_reserve_mutex);
+		if (atomic_read(&active_events) == 0) {
+			r = request_irq(irq, pmu_handle_irq, flags, "Perf_PMU", &loongarch_pmu);
+			if (r < 0) {
+				mutex_unlock(&pmu_reserve_mutex);
+				pr_warn("PMU IRQ request failed\n");
+				return -ENODEV;
+			}
+		}
+		atomic_inc(&active_events);
+		mutex_unlock(&pmu_reserve_mutex);
+	}
+
+	return __hw_perf_event_init(event);
+}
+
+static struct pmu pmu = {
+	.pmu_enable	= loongarch_pmu_enable,
+	.pmu_disable	= loongarch_pmu_disable,
+	.event_init	= loongarch_pmu_event_init,
+	.add		= loongarch_pmu_add,
+	.del		= loongarch_pmu_del,
+	.start		= loongarch_pmu_start,
+	.stop		= loongarch_pmu_stop,
+	.read		= loongarch_pmu_read,
+};
+
+static unsigned int loongarch_pmu_perf_event_encode(const struct loongarch_perf_event *pev)
+{
+	return (pev->event_id & 0xff);
+}
+
+static const struct loongarch_perf_event *loongarch_pmu_map_general_event(int idx)
+{
+	const struct loongarch_perf_event *pev;
+
+	pev = &(*loongarch_pmu.general_event_map)[idx];
+
+	if (pev->event_id == HW_OP_UNSUPPORTED)
+		return ERR_PTR(-ENOENT);
+
+	return pev;
+}
+
+static const struct loongarch_perf_event *loongarch_pmu_map_cache_event(u64 config)
+{
+	unsigned int cache_type, cache_op, cache_result;
+	const struct loongarch_perf_event *pev;
+
+	cache_type = (config >> 0) & 0xff;
+	if (cache_type >= PERF_COUNT_HW_CACHE_MAX)
+		return ERR_PTR(-EINVAL);
+
+	cache_op = (config >> 8) & 0xff;
+	if (cache_op >= PERF_COUNT_HW_CACHE_OP_MAX)
+		return ERR_PTR(-EINVAL);
+
+	cache_result = (config >> 16) & 0xff;
+	if (cache_result >= PERF_COUNT_HW_CACHE_RESULT_MAX)
+		return ERR_PTR(-EINVAL);
+
+	pev = &((*loongarch_pmu.cache_event_map)
+					[cache_type]
+					[cache_op]
+					[cache_result]);
+
+	if (pev->event_id == CACHE_OP_UNSUPPORTED)
+		return ERR_PTR(-ENOENT);
+
+	return pev;
+}
+
+static int validate_group(struct perf_event *event)
+{
+	struct cpu_hw_events fake_cpuc;
+	struct perf_event *sibling, *leader = event->group_leader;
+
+	memset(&fake_cpuc, 0, sizeof(fake_cpuc));
+
+	if (loongarch_pmu_alloc_counter(&fake_cpuc, &leader->hw) < 0)
+		return -EINVAL;
+
+	for_each_sibling_event(sibling, leader) {
+		if (loongarch_pmu_alloc_counter(&fake_cpuc, &sibling->hw) < 0)
+			return -EINVAL;
+	}
+
+	if (loongarch_pmu_alloc_counter(&fake_cpuc, &event->hw) < 0)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void reset_counters(void *arg)
+{
+	int n;
+	int counters = loongarch_pmu.num_counters;
+
+	for (n = 0; n < counters; n++) {
+		loongarch_pmu_write_control(n, 0);
+		loongarch_pmu.write_counter(n, 0);
+	}
+}
+
+static const struct loongarch_perf_event loongson_event_map[PERF_COUNT_HW_MAX] = {
+	PERF_MAP_ALL_UNSUPPORTED,
+	[PERF_COUNT_HW_CPU_CYCLES] = { 0x00 },
+	[PERF_COUNT_HW_INSTRUCTIONS] = { 0x01 },
+	[PERF_COUNT_HW_CACHE_REFERENCES] = { 0x08 },
+	[PERF_COUNT_HW_CACHE_MISSES] = { 0x09 },
+	[PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = { 0x02 },
+	[PERF_COUNT_HW_BRANCH_MISSES] = { 0x03 },
+};
+
+static const struct loongarch_perf_event loongson_cache_map
+				[PERF_COUNT_HW_CACHE_MAX]
+				[PERF_COUNT_HW_CACHE_OP_MAX]
+				[PERF_COUNT_HW_CACHE_RESULT_MAX] = {
+PERF_CACHE_MAP_ALL_UNSUPPORTED,
+[C(L1D)] = {
+	/*
+	 * Like some other architectures (e.g. ARM), the performance
+	 * counters don't differentiate between read and write
+	 * accesses/misses, so this isn't strictly correct, but it's the
+	 * best we can do. Writes and reads get combined.
+	 */
+	[C(OP_READ)] = {
+		[C(RESULT_ACCESS)]	= { 0x8 },
+		[C(RESULT_MISS)]	= { 0x9 },
+	},
+	[C(OP_WRITE)] = {
+		[C(RESULT_ACCESS)]	= { 0x8 },
+		[C(RESULT_MISS)]	= { 0x9 },
+	},
+	[C(OP_PREFETCH)] = {
+		[C(RESULT_ACCESS)]	= { 0xaa },
+		[C(RESULT_MISS)]	= { 0xa9 },
+	},
+},
+[C(L1I)] = {
+	[C(OP_READ)] = {
+		[C(RESULT_ACCESS)]	= { 0x6 },
+		[C(RESULT_MISS)]	= { 0x7 },
+	},
+},
+[C(LL)] = {
+	[C(OP_READ)] = {
+		[C(RESULT_ACCESS)]	= { 0xc },
+		[C(RESULT_MISS)]	= { 0xd },
+	},
+	[C(OP_WRITE)] = {
+		[C(RESULT_ACCESS)]	= { 0xc },
+		[C(RESULT_MISS)]	= { 0xd },
+	},
+},
+[C(ITLB)] = {
+	[C(OP_READ)] = {
+		[C(RESULT_MISS)]    = { 0x3b },
+	},
+},
+[C(DTLB)] = {
+	[C(OP_READ)] = {
+		[C(RESULT_ACCESS)]	= { 0x4 },
+		[C(RESULT_MISS)]	= { 0x3c },
+	},
+	[C(OP_WRITE)] = {
+		[C(RESULT_ACCESS)]	= { 0x4 },
+		[C(RESULT_MISS)]	= { 0x3c },
+	},
+},
+[C(BPU)] = {
+	/* Using the same code for *HW_BRANCH* */
+	[C(OP_READ)] = {
+		[C(RESULT_ACCESS)]  = { 0x02 },
+		[C(RESULT_MISS)]    = { 0x03 },
+	},
+},
+};
+
+static int __hw_perf_event_init(struct perf_event *event)
+{
+	int err;
+	struct hw_perf_event *hwc = &event->hw;
+	struct perf_event_attr *attr = &event->attr;
+	const struct loongarch_perf_event *pev;
+
+	/* Returning LoongArch event descriptor for generic perf event. */
+	if (PERF_TYPE_HARDWARE == event->attr.type) {
+		if (event->attr.config >= PERF_COUNT_HW_MAX)
+			return -EINVAL;
+		pev = loongarch_pmu_map_general_event(event->attr.config);
+	} else if (PERF_TYPE_HW_CACHE == event->attr.type) {
+		pev = loongarch_pmu_map_cache_event(event->attr.config);
+	} else if (PERF_TYPE_RAW == event->attr.type) {
+		/* We are working on the global raw event. */
+		mutex_lock(&raw_event_mutex);
+		pev = loongarch_pmu.map_raw_event(event->attr.config);
+	} else {
+		/* The event type is not (yet) supported. */
+		return -EOPNOTSUPP;
+	}
+
+	if (IS_ERR(pev)) {
+		if (PERF_TYPE_RAW == event->attr.type)
+			mutex_unlock(&raw_event_mutex);
+		return PTR_ERR(pev);
+	}
+
+	/*
+	 * We allow max flexibility on how each individual counter shared
+	 * by the single CPU operates (the mode exclusion and the range).
+	 */
+	hwc->config_base = CSR_PERFCTRL_IE;
+
+	hwc->event_base = loongarch_pmu_perf_event_encode(pev);
+	if (PERF_TYPE_RAW == event->attr.type)
+		mutex_unlock(&raw_event_mutex);
+
+	if (!attr->exclude_user) {
+		hwc->config_base |= CSR_PERFCTRL_PLV3;
+		hwc->config_base |= CSR_PERFCTRL_PLV2;
+	}
+	if (!attr->exclude_kernel) {
+		hwc->config_base |= CSR_PERFCTRL_PLV0;
+	}
+	if (!attr->exclude_hv) {
+		hwc->config_base |= CSR_PERFCTRL_PLV1;
+	}
+
+	hwc->config_base &= M_PERFCTL_CONFIG_MASK;
+	/*
+	 * The event can belong to another cpu. We do not assign a local
+	 * counter for it for now.
+	 */
+	hwc->idx = -1;
+	hwc->config = 0;
+
+	if (!hwc->sample_period) {
+		hwc->sample_period  = loongarch_pmu.max_period;
+		hwc->last_period    = hwc->sample_period;
+		local64_set(&hwc->period_left, hwc->sample_period);
+	}
+
+	err = 0;
+	if (event->group_leader != event)
+		err = validate_group(event);
+
+	event->destroy = hw_perf_event_destroy;
+
+	if (err)
+		event->destroy(event);
+
+	return err;
+}
+
+static void pause_local_counters(void)
+{
+	unsigned long flags;
+	int ctr = loongarch_pmu.num_counters;
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	local_irq_save(flags);
+	do {
+		ctr--;
+		cpuc->saved_ctrl[ctr] = loongarch_pmu_read_control(ctr);
+		loongarch_pmu_write_control(ctr, cpuc->saved_ctrl[ctr] &
+					 ~M_PERFCTL_COUNT_EVENT_WHENEVER);
+	} while (ctr > 0);
+	local_irq_restore(flags);
+}
+
+static void resume_local_counters(void)
+{
+	int ctr = loongarch_pmu.num_counters;
+	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
+
+	do {
+		ctr--;
+		loongarch_pmu_write_control(ctr, cpuc->saved_ctrl[ctr]);
+	} while (ctr > 0);
+}
+
+static const struct loongarch_perf_event *loongarch_pmu_map_raw_event(u64 config)
+{
+	raw_event.event_id = config & 0xff;
+
+	return &raw_event;
+}
+
+static int __init init_hw_perf_events(void)
+{
+	int counters;
+
+	if (!cpu_has_pmp)
+		return -ENODEV;
+
+	pr_info("Performance counters: ");
+	counters = ((read_cpucfg(LOONGARCH_CPUCFG6) & CPUCFG6_PMNUM) >> 4) + 1;
+
+	loongarch_pmu.num_counters = counters;
+	loongarch_pmu.max_period = (1ULL << 63) - 1;
+	loongarch_pmu.valid_count = (1ULL << 63) - 1;
+	loongarch_pmu.overflow = 1ULL << 63;
+	loongarch_pmu.name = "loongarch/loongson64";
+	loongarch_pmu.read_counter = loongarch_pmu_read_counter;
+	loongarch_pmu.write_counter = loongarch_pmu_write_counter;
+	loongarch_pmu.map_raw_event = loongarch_pmu_map_raw_event;
+	loongarch_pmu.general_event_map = &loongson_event_map;
+	loongarch_pmu.cache_event_map = &loongson_cache_map;
+
+	on_each_cpu(reset_counters, NULL, 1);
+
+	pr_cont("%s PMU enabled, %d %d-bit counters available to each CPU.\n",
+			loongarch_pmu.name, counters, 64);
+
+	perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
+
+	return 0;
+}
+early_initcall(init_hw_perf_events);

arch/loongarch/kernel/perf_regs.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 2013 Cavium, Inc.
+ */
+
+#include <linux/perf_event.h>
+
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_32BIT
+u64 perf_reg_abi(struct task_struct *tsk)
+{
+	return PERF_SAMPLE_REGS_ABI_32;
+}
+#else /* Must be CONFIG_64BIT */
+u64 perf_reg_abi(struct task_struct *tsk)
+{
+	if (test_tsk_thread_flag(tsk, TIF_32BIT_REGS))
+		return PERF_SAMPLE_REGS_ABI_32;
+	else
+		return PERF_SAMPLE_REGS_ABI_64;
+}
+#endif /* CONFIG_32BIT */
+
+int perf_reg_validate(u64 mask)
+{
+	if (!mask)
+		return -EINVAL;
+	if (mask & ~((1ull << PERF_REG_LOONGARCH_MAX) - 1))
+		return -EINVAL;
+	return 0;
+}
+
+u64 perf_reg_value(struct pt_regs *regs, int idx)
+{
+	if (WARN_ON_ONCE((u32)idx >= PERF_REG_LOONGARCH_MAX))
+		return 0;
+
+	if ((u32)idx == PERF_REG_LOONGARCH_PC)
+		return regs->csr_era;
+
+	return regs->regs[idx];
+}
+
+void perf_get_regs_user(struct perf_regs *regs_user,
+			struct pt_regs *regs)
+{
+	regs_user->regs = task_pt_regs(current);
+	regs_user->abi = perf_reg_abi(current);
+}