Re: [PATCH] riscv: Setup exception vector for K210 properly

[Anup Patel]

On Tue, Aug 11, 2020 at 12:07 PM Qiu Wenbo <qiuwenbo@xxxxxxxxxxxxxx> wrote:
>
> Exception vector is missing on nommu platform and it is a big issue.
> This patch is tested in Sipeed MAIX Bit Dev Board.
>
> Fixes: 79b1feba5455 ("RISC-V: Setup exception vector early")
> Signed-off-by: Qiu Wenbo <qiuwenbo@xxxxxxxxxxxxxx>
> ---
>  arch/riscv/kernel/smpboot.c |  1 +
>  arch/riscv/kernel/traps.c   | 11 ++++++++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 356825a57551..23cde0ceb39d 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -154,6 +154,7 @@ asmlinkage __visible void smp_callin(void)
>         mmgrab(mm);
>         current->active_mm = mm;
>
> +       trap_init();
>         notify_cpu_starting(curr_cpuid);
>         update_siblings_masks(curr_cpuid);
>         set_cpu_online(curr_cpuid, 1);
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index ad14f4466d92..a390239818ae 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -174,7 +174,16 @@ int is_valid_bugaddr(unsigned long pc)
>  }
>  #endif /* CONFIG_GENERIC_BUG */
>
> -/* stvec & scratch is already set from head.S */
> +/* stvec & scratch is already set from head.S when mmu is enabled */
>  void trap_init(void)
>  {
> +#ifndef CONFIG_MMU
> +       /*
> +        * Set sup0 scratch register to 0, indicating to exception vector
> +        * that we are presently executing in the kernel
> +        */
> +       csr_write(CSR_SCRATCH, 0);
> +       /* Set the exception vector address */
> +       csr_write(CSR_TVEC, &handle_exception);
> +#endif
>  }
> --
> 2.28.0
>

This issue seems to be only on the latest master branch of
Linux stable tree so this fix need not be a stable fix.

For MMU kernel, the CSR_TVEC is setup in relocate() function
called from secondary_start_common() function of head.S

For NoMMU kernel, we should set CSR_TVEC directly in
secondary_start_common() function as "#else" case of the
"#ifdef CONFIG_MMU".

Regards,
Anup