drivers: perf: ctr_get_width function for legacy is not defined

With parameters CONFIG_RISCV_PMU_LEGACY=y and CONFIG_RISCV_PMU_SBI=n
linux kernel crashes when you try perf record:

$ perf record ls
[ 46.749286] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 46.750199] Oops [#1]
[ 46.750342] Modules linked in:
[ 46.750608] CPU: 0 PID: 107 Comm: perf-exec Not tainted 6.6.0 #2
[ 46.750906] Hardware name: riscv-virtio,qemu (DT)
[ 46.751184] epc : 0x0
[ 46.751430] ra : arch_perf_update_userpage+0x54/0x13e
[ 46.751680] epc : 0000000000000000 ra : ffffffff8072ee52 sp : ff2000000022b8f0
[ 46.751958] gp : ffffffff81505988 tp : ff6000000290d400 t0 : ff2000000022b9c0
[ 46.752229] t1 : 0000000000000001 t2 : 0000000000000003 s0 : ff2000000022b930
[ 46.752451] s1 : ff600000028fb000 a0 : 0000000000000000 a1 : ff600000028fb000
[ 46.752673] a2 : 0000000ae2751268 a3 : 00000000004fb708 a4 : 0000000000000004
[ 46.752895] a5 : 0000000000000000 a6 : 000000000017ffe3 a7 : 00000000000000d2
[ 46.753117] s2 : ff600000028fb000 s3 : 0000000ae2751268 s4 : 0000000000000000
[ 46.753338] s5 : ffffffff8153e290 s6 : ff600000863b9000 s7 : ff60000002961078
[ 46.753562] s8 : ff60000002961048 s9 : ff60000002961058 s10: 0000000000000001
[ 46.753783] s11: 0000000000000018 t3 : ffffffffffffffff t4 : ffffffffffffffff
[ 46.754005] t5 : ff6000000292270c t6 : ff2000000022bb30
[ 46.754179] status: 0000000200000100 badaddr: 0000000000000000 cause: 000000000000000c
[ 46.754653] Code: Unable to access instruction at 0xffffffffffffffec.
[ 46.754939] ---[ end trace 0000000000000000 ]---
[ 46.755131] note: perf-exec[107] exited with irqs disabled
[ 46.755546] note: perf-exec[107] exited with preempt_count 4

This happens because in the legacy case the ctr_get_width function was not
defined, but it is used in arch_perf_update_userpage.

Also remove extra check in riscv_pmu_ctr_get_width_mask

Signed-off-by: Vadim Shakirov <vadim.shakirov@syntacore.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Fixes: cc4c07c ("drivers: perf: Implement perf event mmap support  in the SBI backend")
Link: https://lore.kernel.org/r/20240227170002.188671-3-vadim.shakirov@syntacore.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

drivers/perf/riscv_pmu.c

@@ -150,19 +150,11 @@ u64 riscv_pmu_ctr_get_width_mask(struct perf_event *event)
 	struct riscv_pmu *rvpmu = to_riscv_pmu(event->pmu);
 	struct hw_perf_event *hwc = &event->hw;
 
-	if (!rvpmu->ctr_get_width)
-	/**
-	 * If the pmu driver doesn't support counter width, set it to default
-	 * maximum allowed by the specification.
-	 */
-		cwidth = 63;
-	else {
-		if (hwc->idx == -1)
-			/* Handle init case where idx is not initialized yet */
-			cwidth = rvpmu->ctr_get_width(0);
-		else
-			cwidth = rvpmu->ctr_get_width(hwc->idx);
-	}
+	if (hwc->idx == -1)
+		/* Handle init case where idx is not initialized yet */
+		cwidth = rvpmu->ctr_get_width(0);
+	else
+		cwidth = rvpmu->ctr_get_width(hwc->idx);
 
 	return GENMASK_ULL(cwidth, 0);
 }

drivers/perf/riscv_pmu_legacy.c

@@ -37,6 +37,12 @@ static int pmu_legacy_event_map(struct perf_event *event, u64 *config)
 	return pmu_legacy_ctr_get_idx(event);
 }
 
+/* cycle & instret are always 64 bit, one bit less according to SBI spec */
+static int pmu_legacy_ctr_get_width(int idx)
+{
+	return 63;
+}
+
 static u64 pmu_legacy_read_ctr(struct perf_event *event)
 {
 	struct hw_perf_event *hwc = &event->hw;
@@ -111,7 +117,7 @@ static void pmu_legacy_init(struct riscv_pmu *pmu)
 	pmu->ctr_stop = NULL;
 	pmu->event_map = pmu_legacy_event_map;
 	pmu->ctr_get_idx = pmu_legacy_ctr_get_idx;
-	pmu->ctr_get_width = NULL;
+	pmu->ctr_get_width = pmu_legacy_ctr_get_width;
 	pmu->ctr_clear_idx = NULL;
 	pmu->ctr_read = pmu_legacy_read_ctr;
 	pmu->event_mapped = pmu_legacy_event_mapped;