unrecoverable exception on G5 with CONFIG_PPC_EARLY_DEBUG enabled

[Denis Kirjanov]

On 6/6/16, Michael Ellerman <mpe at ellerman.id.au> wrote:
> On Mon, 2016-06-06 at 10:52 +0300, Denis Kirjanov wrote:
>
>> Update: now with the proper mailing address.
>>
>> Hi,
>>
>> Posting if anyone knows how to quickly fix it :)
>
> Sorry but no.
>
>> Enabling  CONFIG_PPC_EARLY_DEBUG on my quad G5 causes kernel to die
>> with the  unrecoverable exception 4100.
>
> That means you took a SLB miss when MSR_RI was off.
>
> What's at c000000000ace328 ?
>
>> I haven't bisected this yet. Photo attached.
>
> A bisect would be awesome.

Ok, the issue was introduced by the commit
caca285e5ab4a7a19fede51688106ceed6fc45dd (powerpc/mm/radix: Use
STD_MMU_64 to properly isolate hash related code) and 970mp dies on
the following condition:
+BEGIN_MMU_FTR_SECTION
        bl      slb_allocate_realmode
-
+END_MMU_FTR_SECTION_IFCLR(MMU_FTR_RADIX)

In my config I've enabled radix MMU lookup but in my understanding
only recent IBM  machines support this feature and we have to call SLB
entry through slb_allocate_realmode on HPTE machine?

Thanks!


>
> cheers
>
>