Re: [PATCH v2 3/6] RISC-V: Check scalar unaligned access on all CPUs

Conor Dooley
2024-06-14T08:23:43Z

[-- Attachment #1: Type: text/plain, Size: 4094 bytes --]

On Thu, Jun 13, 2024 at 03:16:12PM -0400, Jesse Taube wrote:
> Originally, the check_unaligned_access_emulated_all_cpus function
> only checked the boot hart. This fixes the function to check all
> harts.

This seems like it should be split out and get a Fixes: tag & a cc:
stable.

> Check for Zicclsm before checking for unaligned access. This will
> greatly reduce the boot up time as finding the access speed is no longer
> necessary.
>
> Signed-off-by: Jesse Taube <jesse@rivosinc.com>
> ---
> V1 -> V2:
> - New patch
> ---
> arch/riscv/kernel/traps_misaligned.c | 23 ++++++----------------
> arch/riscv/kernel/unaligned_access_speed.c | 23 +++++++++++++---------
> 2 files changed, 20 insertions(+), 26 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index b62d5a2f4541..8fadbe00dd62 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -526,31 +526,17 @@ int handle_misaligned_store(struct pt_regs *regs)
> return 0;
> }
>
> -static bool check_unaligned_access_emulated(int cpu)
> +static void check_unaligned_access_emulated(struct work_struct *unused)
> {
> + int cpu = smp_processor_id();
> long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
> unsigned long tmp_var, tmp_val;
> - bool misaligned_emu_detected;
>
> *mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
>
> __asm__ __volatile__ (
> " "REG_L" %[tmp], 1(%[ptr])\n"
> : [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory");
> -
> - misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED);
> - /*
> - * If unaligned_ctl is already set, this means that we detected that all
> - * CPUS uses emulated misaligned access at boot time. If that changed
> - * when hotplugging the new cpu, this is something we don't handle.
> - */
> - if (unlikely(unaligned_ctl && !misaligned_emu_detected)) {
> - pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n");
> - while (true)
> - cpu_relax();
> - }
> -
> - return misaligned_emu_detected;
> }
>
> bool check_unaligned_access_emulated_all_cpus(void)
> @@ -562,8 +548,11 @@ bool check_unaligned_access_emulated_all_cpus(void)
> * accesses emulated since tasks requesting such control can run on any
> * CPU.
> */
> + schedule_on_each_cpu(check_unaligned_access_emulated);
> +
> for_each_online_cpu(cpu)
> - if (!check_unaligned_access_emulated(cpu))
> + if (per_cpu(misaligned_access_speed, cpu)
> + != RISCV_HWPROBE_MISALIGNED_EMULATED)
> return false;
>
> unaligned_ctl = true;
> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
> index a9a6bcb02acf..70c1588fc353 100644
> --- a/arch/riscv/kernel/unaligned_access_speed.c
> +++ b/arch/riscv/kernel/unaligned_access_speed.c
> @@ -259,23 +259,28 @@ static int check_unaligned_access_speed_all_cpus(void)
> kfree(bufs);
> return 0;
> }
> +#endif /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
>
> static int check_unaligned_access_all_cpus(void)
> {
> - bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> + bool all_cpus_emulated;
> + int cpu;
>
> + if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICCLSM)) {
> + for_each_online_cpu(cpu) {
> + per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
> + }
> + return 0;
> + }
> +
> + all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
> +
> +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS

Can we make this an IS_ENABLED() please?

Thanks,
Conor.

> if (!all_cpus_emulated)
> return check_unaligned_access_speed_all_cpus();
> +#endif
>
> return 0;
> }
> -#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
> -static int check_unaligned_access_all_cpus(void)
> -{
> - check_unaligned_access_emulated_all_cpus();
> -
> - return 0;
> -}
> -#endif
>
> arch_initcall(check_unaligned_access_all_cpus);
> --
> 2.43.0
>

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]