Subject: Re: [PATCH 2/2] powerpc: Fix crash at boot with CONFIG_PPC_RADIX_MMU=n

From: Balbir Singh <[email-masked]>
Date: Thu, 12 May 2016 11:32:36 +1000

On Wed, 11 May 2016 16:47:11 +1000
Michael Ellerman <[email-masked]> wrote:

> Currently a kernel that is built with CONFIG_PPC_RADIX_MMU=n, and then
> booted on a 64-bit Hash MMU system will crash on the first SLB miss,
> typically with an oops something like:
> 
>   Unrecoverable exception 4100 at c000000000969504
>   cpu 0x0: Vector: 4100  at [c000000000de78e0]
>       pc: c000000000969504: memmap_init_zone+0x160/0x2dc
>       lr: c0000000009694b0: memmap_init_zone+0x10c/0x2dc
>   ...
>   [c000000000de7b60] c000000000968ec8 init_currently_empty_zone+0x3c/0x11c (unreliable)
>   [c000000000de7bf0] c000000000969bc0 free_area_init_node+0x540/0x688
>   [c000000000de7cf0] c000000000c4b3b4 free_area_init_nodes+0x7b4/0x864
>   [c000000000de7df0] c000000000c2fce0 paging_init+0x88/0xa4
>   [c000000000de7e60] c000000000c2b49c setup_arch+0x29c/0x2ec
>   [c000000000de7f00] c000000000c23b7c start_kernel+0x88/0x524
>   [c000000000de7f90] c000000000008c60 start_here_common+0x20/0xa0
> 
> This is caused by the branch in slb_miss_realmode() that jumps directly
> to the unrecoverable case when MMU_FTR_RADIX is set:
> 
>   BEGIN_MMU_FTR_SECTION
>   	b	2f
>   END_MMU_FTR_SECTION_IFSET(MMU_FTR_RADIX)
> 

This makes sense and its a good way to avoid plenty of #ifdefs around code

Acked-by: Balbir Singh <[email-masked]>

Balbir Singh