Re: [PATCH] RISC-V: Check clint_time_val before use

[Damien Le Moal]

On Sat, 2020-09-26 at 12:57 +0530, Anup Patel wrote:
> The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
> because the get_cycles() and friends are called very early from
> rand_initialize() before CLINT driver is probed. To fix this, we
> should check clint_time_val before use in get_cycles() and friends.
> 
> Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
> for M-mode systems")
> Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> ---
>  arch/riscv/include/asm/timex.h | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
> index 7f659dda0032..52b42bb1602c 100644
> --- a/arch/riscv/include/asm/timex.h
> +++ b/arch/riscv/include/asm/timex.h
> @@ -17,18 +17,24 @@ typedef unsigned long cycles_t;
>  #ifdef CONFIG_64BIT
>  static inline cycles_t get_cycles(void)
>  {
> -	return readq_relaxed(clint_time_val);
> +	if (clint_time_val)
> +		return readq_relaxed(clint_time_val);
> +	return 0;
>  }
>  #else /* !CONFIG_64BIT */
>  static inline u32 get_cycles(void)
>  {
> -	return readl_relaxed(((u32 *)clint_time_val));
> +	if (clint_time_val)
> +		return readl_relaxed(((u32 *)clint_time_val));
> +	return 0;
>  }
>  #define get_cycles get_cycles
>  
>  static inline u32 get_cycles_hi(void)
>  {
> -	return readl_relaxed(((u32 *)clint_time_val) + 1);
> +	if (clint_time_val)
> +		return readl_relaxed(((u32 *)clint_time_val) + 1);
> +	return 0
>  }
>  #define get_cycles_hi get_cycles_hi
>  #endif /* CONFIG_64BIT */

Applying this on top of rc6, I now get a hang on Kendryte boot...
No problems without the patch on the other hand.


-- 
Damien Le Moal
Western Digital