drivers/perf: riscv: Implement SBI PMU snapshot function

SBI v2.0 SBI introduced PMU snapshot feature which adds the following
features.

1. Read counter values directly from the shared memory instead of
csr read.
2. Start multiple counters with initial values with one SBI call.

These functionalities optimizes the number of traps to the higher
privilege mode. If the kernel is in VS mode while the hypervisor
deploy trap & emulate method, this would minimize all the hpmcounter
CSR read traps. If the kernel is running in S-mode, the benefits
reduced to CSR latency vs DRAM/cache latency as there is no trap
involved while accessing the hpmcounter CSRs.

In both modes, it does saves the number of ecalls while starting
multiple counter together with an initial values. This is a likely
scenario if multiple counters overflow at the same time.
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-10-atishp@rivosinc.comSigned-off-by: Anup Patel <anup@brainfault.org>

drivers/perf/riscv_pmu.c

@@ -191,8 +191,6 @@ void riscv_pmu_stop(struct perf_event *event, int flags)
 	struct hw_perf_event *hwc = &event->hw;
 	struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
 
-	WARN_ON_ONCE(hwc->state & PERF_HES_STOPPED);
-
 	if (!(hwc->state & PERF_HES_STOPPED)) {
 		if (rvpmu->ctr_stop) {
 			rvpmu->ctr_stop(event, 0);
@@ -408,6 +406,7 @@ struct riscv_pmu *riscv_pmu_alloc(void)
 		cpuc->n_events = 0;
 		for (i = 0; i < RISCV_MAX_COUNTERS; i++)
 			cpuc->events[i] = NULL;
+		cpuc->snapshot_addr = NULL;
 	}
 	pmu->pmu = (struct pmu) {
 		.event_init	= riscv_pmu_event_init,

include/linux/perf/riscv_pmu.h

@@ -39,6 +39,14 @@ struct cpu_hw_events {
 	DECLARE_BITMAP(used_hw_ctrs, RISCV_MAX_COUNTERS);
 	/* currently enabled firmware counters */
 	DECLARE_BITMAP(used_fw_ctrs, RISCV_MAX_COUNTERS);
+	/* The virtual address of the shared memory where counter snapshot will be taken */
+	void *snapshot_addr;
+	/* The physical address of the shared memory where counter snapshot will be taken */
+	phys_addr_t snapshot_addr_phys;
+	/* Boolean flag to indicate setup is already done */
+	bool snapshot_set_done;
+	/* A shadow copy of the counter values to avoid clobbering during multiple SBI calls */
+	u64 snapshot_cval_shcopy[RISCV_MAX_COUNTERS];
 };
 
 struct riscv_pmu {