Re: [PATCH] MIPS: Make sure ebase address is in KSEG0

[Paul Burton <paulburton@kernel.org>]

Hi Huacai,

On Thu, Nov 21, 2019 at 07:30:20PM +0800, Huacai Chen wrote:
> Dynamically allocated ebase address above 0x20000000 can be triggered
> by some special physical memory layout, or just by a "big kernel + big
> initrd + big swiotlb" configuration.
> 
> For MIPS32, ebase address above 0x20000000 is unusable, for MIPS64 it
> is usable but this case is warned. However, this warning is useless
> because it is unfixable in a specific system configuration. So we just
> use CKSEG0 as a fallback.

I'd prefer that we don't assume there's memory at physical address zero
- that property doesn't hold for all systems.

How about the change I suggested previously over here:

  https://lore.kernel.org/linux-mips/20191108191149.bbq3h4xp4famsh2n@lantea.localdomain/

Would that work for you?

Thanks,
    Paul

> Signed-off-by: Huacai Chen <chenhc@lemote.com>
> ---
>  arch/mips/kernel/traps.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
> index 9d9b2a4..7393f33 100644
> --- a/arch/mips/kernel/traps.c
> +++ b/arch/mips/kernel/traps.c
> @@ -2306,10 +2306,15 @@ void __init trap_init(void)
>  		 * EVA is special though as it allows segments to be rearranged
>  		 * and to become uncached during cache error handling.
>  		 */
> -		if (!IS_ENABLED(CONFIG_EVA) && !WARN_ON(ebase_pa >= 0x20000000))
> +		if (ebase_pa < 0x20000000)
>  			ebase = CKSEG0ADDR(ebase_pa);
> -		else
> +		else if (IS_ENABLED(CONFIG_EVA))
>  			ebase = (unsigned long)phys_to_virt(ebase_pa);
> +		else {
> +			memblock_free(ebase_pa, vec_size);
> +			ebase = CKSEG0;
> +			memblock_reserve(virt_to_phys((void *)ebase), vec_size);
> +		}
>  	}
>  
>  	if (cpu_has_mmips) {
> -- 
> 2.7.0
>