Subject: Re: [PATCH v2 00/15] powerpc/32s: Use BATs/LTLBs for STRICT_KERNEL_RWX

From: Jonathan Neuschäfer <[email-masked]>
Date: Wed, 16 Jan 2019 14:16:37 +0100

On Wed, Jan 16, 2019 at 07:55:29AM +0100, Christophe Leroy wrote:
> Le 16/01/2019 à 01:35, Jonathan Neuschäfer a écrit :
> > Thinning the kernel down a bit actually makes it boot again. Ooops...!
> > Maybe enabling CONFIG_STRICT_KERNEL_RWX has made it just large enough to
> > fail the hash table allocation, but there may have been other factors
> > involved (I'm not sure exactly).  Sorry for the confusion!
> 
> Ok, that must be the reason. Thanks for testing.
> 
> What about the following modification which maps a second 256Mb BAT, does it
> helps ?
> 
> 
> 
> diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> index c2f564690778..ea574596de37 100644
> --- a/arch/powerpc/kernel/head_32.S
> +++ b/arch/powerpc/kernel/head_32.S
> @@ -1160,6 +1160,14 @@ initial_bats:
>  	mtspr	SPRN_DBAT0U,r11		/* bit in upper BAT register */
>  	mtspr	SPRN_IBAT0L,r8
>  	mtspr	SPRN_IBAT0U,r11
> +#ifdef CONFIG_WII
> +	addis	r11,r11,0x10000000@h
> +	addis	r8,r8,0x10000000@h
> +	mtspr	SPRN_DBAT2L,r8
> +	mtspr	SPRN_DBAT2U,r11
> +	mtspr	SPRN_IBAT2L,r8
> +	mtspr	SPRN_IBAT2U,r11
> +#endif
>  	isync
>  	blr
> 
> diff --git a/arch/powerpc/mm/ppc_mmu_32.c b/arch/powerpc/mm/ppc_mmu_32.c
> index 3f4193201ee7..a334fd5210a8 100644
> --- a/arch/powerpc/mm/ppc_mmu_32.c
> +++ b/arch/powerpc/mm/ppc_mmu_32.c
> @@ -259,6 +259,8 @@ void setup_initial_memory_limit(phys_addr_t
> first_memblock_base,
>  	/* 601 can only access 16MB at the moment */
>  	if (PVR_VER(mfspr(SPRN_PVR)) == 1)
>  		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x01000000));
> +	else if (IS_ENABLED(CONFIG_WII))
> +		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x20000000));
>  	else /* Anything else has 256M mapped */
>  		memblock_set_current_limit(min_t(u64, first_memblock_size, 0x10000000));
>  }

I haven't tested it, but this patch won't be enough, because we're only
looking at the first memblock, and the additional memory in the Wii
(MEM2) is the second memblock.

Jonathan