Re: [PATCH] powerpc/Kconfig: Force THREAD_SHIFT to at least 14 with KASAN

Christophe Leroy
2022-05-31T06:27:05Z

Le 31/05/2022 à 08:16, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
>> Allthough 14 is the default THREAD_SHIFT when KASAN is selected,
>> taking an old config may keep 13 when CONFIG_EXPERT is selected.
>>
>> Force it to 14 as a minimum when KASAN is selected.
>>
>> Also default to 15 when KASAN on PPC64.
>>
>> Reported-by: Erhard Furtner <erhard_f@mailbox.org>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>> arch/powerpc/Kconfig | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> I was thinking of doing it in C, similar to the way arm64 handles it.
>
> Something like below. It means we always double the stack size when
> KASAN is enabled. I think it's preferable, as it will always work
> regardless of whether the user has an old .config (or is bisectting)?

Yes good idea.

I leave it to you then.

You can therefore also remove the default value for KASAN in Kconfig.

Christophe

>
> cheers
>
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index 125328d1b980..c9735f93f8e6 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -14,12 +14,17 @@
>
> #ifdef __KERNEL__
>
> -#if defined(CONFIG_VMAP_STACK) && CONFIG_THREAD_SHIFT < PAGE_SHIFT
> -#define THREAD_SHIFT PAGE_SHIFT
> +#ifdef CONFIG_KASAN
> +#define THREAD_SHIFT (CONFIG_THREAD_SHIFT + 1)
> #else
> #define THREAD_SHIFT CONFIG_THREAD_SHIFT
> #endif
>
> +#if defined(CONFIG_VMAP_STACK) && THREAD_SHIFT < PAGE_SHIFT
> +#undef THREAD_SHIFT
> +#define THREAD_SHIFT PAGE_SHIFT
> +#endif
> +
> #define THREAD_SIZE (1 << THREAD_SHIFT)
>
> /*
>
>