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

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Message-ID: <CY4PR04MB375124E6D2AD38BF1D71C1D5E7450@CY4PR04MB3751.namprd04.prod.outlook.com>
Date:   Tue, 11 Aug 2020 06:42:15 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Qiu Wenbo <qiuwenbo@...tium.com.cn>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>
CC:     Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <Atish.Patra@....com>,
        Anup Patel <anup@...infault.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Zong Li <zong.li@...ive.com>,
        Greentime Hu <greentime.hu@...ive.com>,
        Vincent Chen <vincent.chen@...ive.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: Setup exception vector for K210 properly

On 2020/08/11 15:38, Qiu Wenbo 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@...tium.com.cn>
> ---
>  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
>  }
> 

Looks OK to me. But out of curiosity, how did you trigger a problem ? I never
got any weird exceptions with my busybox userspace.

-- 
Damien Le Moal
Western Digital Research