linux-kernel - Re: [PATCH 1/4] RISC-V: Setup exception vector early

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Message-ID: <mhng-8ce8d920-4b65-432c-8b51-8d81f55936c0@palmerdabbelt-glaptop1>
Date:   Fri, 24 Jul 2020 22:12:38 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Atish Patra <Atish.Patra@....com>
CC:     linux-kernel@...r.kernel.org, Atish Patra <Atish.Patra@....com>,
        aou@...s.berkeley.edu, Anup Patel <Anup.Patel@....com>,
        greentime.hu@...ive.com, linux-riscv@...ts.infradead.org,
        Paul Walmsley <paul.walmsley@...ive.com>, sudeep.holla@....com,
        vincent.chen@...ive.com, zong.li@...ive.com
Subject:     Re: [PATCH 1/4] RISC-V: Setup exception vector early

On Wed, 15 Jul 2020 16:30:06 PDT (-0700), Atish Patra wrote:
> The trap vector is set only in trap_init which may be too late in some
> cases. Early ioremap/efi spits many warning messages which may be useful.
>
> Setup the trap vector early so that any warning/bug can be handled before
> generic code invokes trap_init.
>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
>  arch/riscv/kernel/head.S    | 10 ++++++++--
>  arch/riscv/kernel/smpboot.c |  1 -
>  arch/riscv/kernel/traps.c   |  8 +-------
>  3 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 7ed1b22950fd..d0c5c316e9bb 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -77,10 +77,16 @@ relocate:
>  	csrw CSR_SATP, a0
>  .align 2
>  1:
> -	/* Set trap vector to spin forever to help debug */
> -	la a0, .Lsecondary_park
> +	/* Set trap vector to exception handler */
> +	la a0, handle_exception
>  	csrw CSR_TVEC, a0
>
> +	/*
> +	 * Set sup0 scratch register to 0, indicating to exception vector that
> +	 * we are presently executing in kernel.
> +	 */
> +	csrw CSR_SCRATCH, zero
> +
>  	/* Reload the global pointer */
>  .option push
>  .option norelax
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 4e9922790f6e..5a9c127a380e 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -154,7 +154,6 @@ asmlinkage __visible void smp_callin(void)
>  	mmgrab(mm);
>  	current->active_mm = mm;
>
> -	trap_init();
>  	notify_cpu_starting(smp_processor_id());
>  	update_siblings_masks(smp_processor_id());
>  	set_cpu_online(smp_processor_id(), 1);
> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> index 7d95cce5e47c..ad14f4466d92 100644
> --- a/arch/riscv/kernel/traps.c
> +++ b/arch/riscv/kernel/traps.c
> @@ -174,13 +174,7 @@ int is_valid_bugaddr(unsigned long pc)
>  }
>  #endif /* CONFIG_GENERIC_BUG */
>
> +/* stvec & scratch is already set from head.S */
>  void trap_init(void)
>  {
> -	/*
> -	 * 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);
>  }

While I think these are all actual fixes, it's pretty late in the cycle here so
I'm going to a bit on the careful side and only take the patches that actually
manifest as bugs in the current port.  Assuming this doesn't manifest until
early_ioremap is enabled (and we don't do that yet), I've put it on for-next.

LMK if I'm wrong about this, or the following ones.

Thanks!