drivers: perf: Check find_first_bit() return value

We must check the return value of find_first_bit() before using the
return value as an index array since it happens to overflow the array
and then panic:

[  107.318430] Kernel BUG [#1]
[  107.319434] CPU: 3 PID: 1238 Comm: kill Tainted: G            E      6.6.0-rc6ubuntu-defconfig #2
[  107.319465] Hardware name: riscv-virtio,qemu (DT)
[  107.319551] epc : pmu_sbi_ovf_handler+0x3a4/0x3ae
[  107.319840]  ra : pmu_sbi_ovf_handler+0x52/0x3ae
[  107.319868] epc : ffffffff80a0a77c ra : ffffffff80a0a42a sp : ffffaf83fecda350
[  107.319884]  gp : ffffffff823961a8 tp : ffffaf8083db1dc0 t0 : ffffaf83fecda480
[  107.319899]  t1 : ffffffff80cafe62 t2 : 000000000000ff00 s0 : ffffaf83fecda520
[  107.319921]  s1 : ffffaf83fecda380 a0 : 00000018fca29df0 a1 : ffffffffffffffff
[  107.319936]  a2 : 0000000001073734 a3 : 0000000000000004 a4 : 0000000000000000
[  107.319951]  a5 : 0000000000000040 a6 : 000000001d1c8774 a7 : 0000000000504d55
[  107.319965]  s2 : ffffffff82451f10 s3 : ffffffff82724e70 s4 : 000000000000003f
[  107.319980]  s5 : 0000000000000011 s6 : ffffaf8083db27c0 s7 : 0000000000000000
[  107.319995]  s8 : 0000000000000001 s9 : 00007fffb45d6558 s10: 00007fffb45d81a0
[  107.320009]  s11: ffffaf7ffff60000 t3 : 0000000000000004 t4 : 0000000000000000
[  107.320023]  t5 : ffffaf7f80000000 t6 : ffffaf8000000000
[  107.320037] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
[  107.320081] [<ffffffff80a0a77c>] pmu_sbi_ovf_handler+0x3a4/0x3ae
[  107.320112] [<ffffffff800b42d0>] handle_percpu_devid_irq+0x9e/0x1a0
[  107.320131] [<ffffffff800ad92c>] generic_handle_domain_irq+0x28/0x36
[  107.320148] [<ffffffff8065f9f8>] riscv_intc_irq+0x36/0x4e
[  107.320166] [<ffffffff80caf4a0>] handle_riscv_irq+0x54/0x86
[  107.320189] [<ffffffff80cb0036>] do_irq+0x64/0x96
[  107.320271] Code: 85a6 855e b097 ff7f 80e7 9220 b709 9002 4501 bbd9 (9002) 6097
[  107.320585] ---[ end trace 0000000000000000 ]---
[  107.320704] Kernel panic - not syncing: Fatal exception in interrupt
[  107.320775] SMP: stopping secondary CPUs
[  107.321219] Kernel Offset: 0x0 from 0xffffffff80000000
[  107.333051] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

Fixes: 4905ec2f ("RISC-V: Add sscofpmf extension support")
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20231109082128.40777-1-alexghiti@rivosinc.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

drivers/perf/riscv_pmu_sbi.c

@@ -685,6 +685,11 @@ static irqreturn_t pmu_sbi_ovf_handler(int irq, void *dev)
 
 	/* Firmware counter don't support overflow yet */
 	fidx = find_first_bit(cpu_hw_evt->used_hw_ctrs, RISCV_MAX_COUNTERS);
+	if (fidx == RISCV_MAX_COUNTERS) {
+		csr_clear(CSR_SIP, BIT(riscv_pmu_irq_num));
+		return IRQ_NONE;
+	}
+
 	event = cpu_hw_evt->events[fidx];
 	if (!event) {
 		csr_clear(CSR_SIP, BIT(riscv_pmu_irq_num));