[PATCH v2 05/10] riscv: Prepare for user-space perf event mmap support

[Alexandre Ghiti]

Provide all the necessary bits in the generic riscv pmu driver to be
able to mmap perf events in userspace: the heavy lifting lies in the
driver backend, namely the legacy and sbi implementations.

Note that arch_perf_update_userpage is almost a copy of arm64 code.

Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
---
 arch/riscv/kernel/Makefile     |  2 +-
 arch/riscv/kernel/perf_event.c | 58 ++++++++++++++++++++++++++++++++++
 drivers/perf/riscv_pmu.c       | 41 ++++++++++++++++++++++++
 include/linux/perf/riscv_pmu.h |  4 +++
 4 files changed, 104 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/kernel/perf_event.c

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 4cf303a779ab..0d215fd9860d 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -70,7 +70,7 @@ obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
 
 obj-$(CONFIG_TRACE_IRQFLAGS)	+= trace_irq.o
 
-obj-$(CONFIG_PERF_EVENTS)	+= perf_callchain.o
+obj-$(CONFIG_PERF_EVENTS)	+= perf_callchain.o perf_event.o
 obj-$(CONFIG_HAVE_PERF_REGS)	+= perf_regs.o
 obj-$(CONFIG_RISCV_SBI)		+= sbi.o
 ifeq ($(CONFIG_RISCV_SBI), y)
diff --git a/arch/riscv/kernel/perf_event.c b/arch/riscv/kernel/perf_event.c
new file mode 100644
index 000000000000..94174a0fc251
--- /dev/null
+++ b/arch/riscv/kernel/perf_event.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/sched_clock.h>
+
+void arch_perf_update_userpage(struct perf_event *event,
+			       struct perf_event_mmap_page *userpg, u64 now)
+{
+	struct clock_read_data *rd;
+	unsigned int seq;
+	u64 ns;
+
+	userpg->cap_user_time = 0;
+	userpg->cap_user_time_zero = 0;
+	userpg->cap_user_time_short = 0;
+	userpg->cap_user_rdpmc =
+		!!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT);
+
+	userpg->pmc_width = 64;
+
+	do {
+		rd = sched_clock_read_begin(&seq);
+
+		userpg->time_mult = rd->mult;
+		userpg->time_shift = rd->shift;
+		userpg->time_zero = rd->epoch_ns;
+		userpg->time_cycles = rd->epoch_cyc;
+		userpg->time_mask = rd->sched_clock_mask;
+
+		/*
+		 * Subtract the cycle base, such that software that
+		 * doesn't know about cap_user_time_short still 'works'
+		 * assuming no wraps.
+		 */
+		ns = mul_u64_u32_shr(rd->epoch_cyc, rd->mult, rd->shift);
+		userpg->time_zero -= ns;
+
+	} while (sched_clock_read_retry(seq));
+
+	userpg->time_offset = userpg->time_zero - now;
+
+	/*
+	 * time_shift is not expected to be greater than 31 due to
+	 * the original published conversion algorithm shifting a
+	 * 32-bit value (now specifies a 64-bit value) - refer
+	 * perf_event_mmap_page documentation in perf_event.h.
+	 */
+	if (userpg->time_shift == 32) {
+		userpg->time_shift = 31;
+		userpg->time_mult >>= 1;
+	}
+
+	/*
+	 * Internal timekeeping for enabled/running/stopped times
+	 * is always computed with the sched_clock.
+	 */
+	userpg->cap_user_time = 1;
+	userpg->cap_user_time_zero = 1;
+	userpg->cap_user_time_short = 1;
+}
diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index ebca5eab9c9b..af69da268246 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -171,6 +171,8 @@ int riscv_pmu_event_set_period(struct perf_event *event)
 
 	local64_set(&hwc->prev_count, (u64)-left);
 
+	perf_event_update_userpage(event);
+
 	return overflow;
 }
 
@@ -267,6 +269,9 @@ static int riscv_pmu_event_init(struct perf_event *event)
 	hwc->idx = -1;
 	hwc->event_base = mapped_event;
 
+	if (rvpmu->event_init)
+		rvpmu->event_init(event);
+
 	if (!is_sampling_event(event)) {
 		/*
 		 * For non-sampling runs, limit the sample_period to half
@@ -283,6 +288,39 @@ static int riscv_pmu_event_init(struct perf_event *event)
 	return 0;
 }
 
+static int riscv_pmu_event_idx(struct perf_event *event)
+{
+	struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
+
+	if (!(event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT))
+		return 0;
+
+	if (rvpmu->csr_index)
+		return rvpmu->csr_index(event) + 1;
+
+	return 0;
+}
+
+static void riscv_pmu_event_mapped(struct perf_event *event, struct mm_struct *mm)
+{
+	struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
+
+	if (rvpmu->event_mapped) {
+		rvpmu->event_mapped(event, mm);
+		perf_event_update_userpage(event);
+	}
+}
+
+static void riscv_pmu_event_unmapped(struct perf_event *event, struct mm_struct *mm)
+{
+	struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
+
+	if (rvpmu->event_unmapped) {
+		rvpmu->event_unmapped(event, mm);
+		perf_event_update_userpage(event);
+	}
+}
+
 struct riscv_pmu *riscv_pmu_alloc(void)
 {
 	struct riscv_pmu *pmu;
@@ -307,6 +345,9 @@ struct riscv_pmu *riscv_pmu_alloc(void)
 	}
 	pmu->pmu = (struct pmu) {
 		.event_init	= riscv_pmu_event_init,
+		.event_mapped	= riscv_pmu_event_mapped,
+		.event_unmapped	= riscv_pmu_event_unmapped,
+		.event_idx	= riscv_pmu_event_idx,
 		.add		= riscv_pmu_add,
 		.del		= riscv_pmu_del,
 		.start		= riscv_pmu_start,
diff --git a/include/linux/perf/riscv_pmu.h b/include/linux/perf/riscv_pmu.h
index 9f70d94942e0..1452c8af3b67 100644
--- a/include/linux/perf/riscv_pmu.h
+++ b/include/linux/perf/riscv_pmu.h
@@ -55,6 +55,10 @@ struct riscv_pmu {
 	void		(*ctr_start)(struct perf_event *event, u64 init_val);
 	void		(*ctr_stop)(struct perf_event *event, unsigned long flag);
 	int		(*event_map)(struct perf_event *event, u64 *config);
+	void		(*event_init)(struct perf_event *event);
+	void		(*event_mapped)(struct perf_event *event, struct mm_struct *mm);
+	void		(*event_unmapped)(struct perf_event *event, struct mm_struct *mm);
+	uint8_t		(*csr_index)(struct perf_event *event);
 
 	struct cpu_hw_events	__percpu *hw_events;
 	struct hlist_node	node;
-- 
2.37.2