Re: [PATCH v5 3/7] RISC-V: Check scalar unaligned access on all CPUs

[Evan Green]

On Wed, Jul 17, 2024 at 11:07 AM Jesse Taube <jesse@xxxxxxxxxxxx> wrote:
>
> Originally, the check_unaligned_access_emulated_all_cpus function
> only checked the boot hart. This fixes the function to check all
> harts.
>
> Fixes: 71c54b3d169d ("riscv: report misaligned accesses emulation to hwprobe")
> Signed-off-by: Jesse Taube <jesse@xxxxxxxxxxxx>
> Reviewed-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>

Reviewed-by: Evan Green <evan@xxxxxxxxxxxx>


> Cc: stable@xxxxxxxxxxxxxxx
> ---
> V1 -> V2:
>  - New patch
> V2 -> V3:
>  - Split patch
> V3 -> V4:
>  - Re-add check for a system where a heterogeneous
>     CPU is hotplugged into a previously homogenous
>     system.
> V4 -> V5:
>  - Change work_struct *unused to work_struct *work __always_unused
> ---
>  arch/riscv/kernel/traps_misaligned.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index b62d5a2f4541..9a1e94383d6d 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -526,11 +526,11 @@ 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 *work __always_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;
>
> @@ -538,19 +538,16 @@ static bool check_unaligned_access_emulated(int cpu)
>                 "       "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)) {
> +       if (unlikely(unaligned_ctl && (*mas_ptr != RISCV_HWPROBE_MISALIGNED_EMULATED))) {
>                 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 +559,11 @@ 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;
> --
> 2.45.2
>