drivers: perf: Fix panic in riscv SBI mmap support
The following panic can happen when mmap is called before the pmu add callback which sets the hardware counter index: this happens for example with the following command `perf record --no-bpf-event -n kill`. [ 99.461486] CPU: 1 PID: 1259 Comm: perf Tainted: G E 6.6.0-rc4ubuntu-defconfig #2 [ 99.461669] Hardware name: riscv-virtio,qemu (DT) [ 99.461748] epc : pmu_sbi_set_scounteren+0x42/0x44 [ 99.462337] ra : smp_call_function_many_cond+0x126/0x5b0 [ 99.462369] epc : ffffffff809f9d24 ra : ffffffff800f93e0 sp : ff60000082153aa0 [ 99.462407] gp : ffffffff82395c98 tp : ff6000009a218040 t0 : ff6000009ab3a4f0 [ 99.462425] t1 : 0000000000000004 t2 : 0000000000000100 s0 : ff60000082153ab0 [ 99.462459] s1 : 0000000000000000 a0 : ff60000098869528 a1 : 0000000000000000 [ 99.462473] a2 : 000000000000001f a3 : 0000000000f00000 a4 : fffffffffffffff8 [ 99.462488] a5 : 00000000000000cc a6 : 0000000000000000 a7 : 0000000000735049 [ 99.462502] s2 : 0000000000000001 s3 : ffffffff809f9ce2 s4 : ff60000098869528 [ 99.462516] s5 : 0000000000000002 s6 : 0000000000000004 s7 : 0000000000000001 [ 99.462530] s8 : ff600003fec98bc0 s9 : ffffffff826c5890 s10: ff600003fecfcde0 [ 99.462544] s11: ff600003fec98bc0 t3 : ffffffff819e2558 t4 : ff1c000004623840 [ 99.462557] t5 : 0000000000000901 t6 : ff6000008feeb890 [ 99.462570] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003 [ 99.462658] [<ffffffff809f9d24>] pmu_sbi_set_scounteren+0x42/0x44 [ 99.462979] Code: 1060 4785 97bb 00d7 8fd9 9073 1067 6422 0141 8082 (9002) 0013 [ 99.463335] Kernel BUG [#2] To circumvent this, try to enable userspace access to the hardware counter when it is selected in addition to when the event is mapped. And vice-versa when the event is stopped/unmapped. Fixes: cc4c07c8 ("drivers: perf: Implement perf event mmap support in the SBI backend") Signed-off-by:Alexandre Ghiti <alexghiti@rivosinc.com> Link: https://lore.kernel.org/r/20231006082010.11963-1-alexghiti@rivosinc.com Cc: stable@vger.kernel.org Signed-off-by: