Re: [External] [PATCH v4 2/9] riscv: smp: fail booting up smp if inconsistent vlen is detected

[yunhui cui]

Hi Andy,

On Fri, Apr 12, 2024 at 2:50 PM Andy Chiu <andy.chiu@xxxxxxxxxx> wrote:
>
> Currently we only support Vector for SMP platforms, that is, all SMP
> cores have the same vlenb. If we happen to detect a mismatching vlen, it
> is better to just fail bootting it up to prevent further race/scheduling
> issues.
>
> Also, move .Lsecondary_park forward and chage `tail smp_callin` into a
> regular call in the early assembly. So a core would be parked right
> after a return from smp_callin. Note that a successful smp_callin
> does not return.
>
> Fixes: 7017858eb2d7 ("riscv: Introduce riscv_v_vsize to record size of Vector context")
> Reported-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-riscv/20240228-vicinity-cornstalk-4b8eb5fe5730@spud/
> Signed-off-by: Andy Chiu <andy.chiu@xxxxxxxxxx>
> ---
> Changelog v4:
>  - update comment also in the assembly code (Yunhui)
> Changelog v2:
>  - update commit message to explain asm code change (Conor)
> ---
>  arch/riscv/kernel/head.S    | 19 ++++++++++++-------
>  arch/riscv/kernel/smpboot.c | 14 +++++++++-----
>  2 files changed, 21 insertions(+), 12 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 4236a69c35cb..a00f7523cb91 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -165,9 +165,20 @@ secondary_start_sbi:
>  #endif
>         call .Lsetup_trap_vector
>         scs_load_current
> -       tail smp_callin
> +       call smp_callin
>  #endif /* CONFIG_SMP */
>
> +.align 2
> +.Lsecondary_park:
> +       /*
> +        * Park this hart if we:
> +        *  - have too many harts on CONFIG_RISCV_BOOT_SPINWAIT
> +        *  - receive an early trap, before setup_trap_vector finished
> +        *  - fail in smp_callin(), as a successful one wouldn't return
> +        */
> +       wfi
> +       j .Lsecondary_park
> +
>  .align 2
>  .Lsetup_trap_vector:
>         /* Set trap vector to exception handler */
> @@ -181,12 +192,6 @@ secondary_start_sbi:
>         csrw CSR_SCRATCH, zero
>         ret
>
> -.align 2
> -.Lsecondary_park:
> -       /* We lack SMP support or have too many harts, so park this hart */
> -       wfi
> -       j .Lsecondary_park
> -
>  SYM_CODE_END(_start)
>
>  SYM_CODE_START(_start_kernel)
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index d41090fc3203..673437ccc13d 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -214,6 +214,15 @@ asmlinkage __visible void smp_callin(void)
>         struct mm_struct *mm = &init_mm;
>         unsigned int curr_cpuid = smp_processor_id();
>
> +       if (has_vector()) {
> +               /*
> +                * Return as early as possible so the hart with a mismatching
> +                * vlen won't boot.
> +                */
> +               if (riscv_v_setup_vsize())
> +                       return;
> +       }
> +
>         /* All kernel threads share the same mm context.  */
>         mmgrab(mm);
>         current->active_mm = mm;
> @@ -226,11 +235,6 @@ asmlinkage __visible void smp_callin(void)
>         numa_add_cpu(curr_cpuid);
>         set_cpu_online(curr_cpuid, 1);
>
> -       if (has_vector()) {
> -               if (riscv_v_setup_vsize())
> -                       elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
> -       }
> -
>         riscv_user_isa_enable();
>
>         /*
>
> --
> 2.44.0.rc2
>
>

Reviewed-by: Yunhui Cui <cuiyunhui@xxxxxxxxxxxxx>


Thanks,
Yunhui