[Skiboot] [PATCH] external/mambo: Disable MEMORY_OVERFLOW

[Oliver O'Halloran]

On Thu, Jul 2, 2020 at 11:56 AM Gustavo Romero
<gromero at linux.vnet.ibm.com> wrote:
>
>
> But just before the 'nop' there is a dcbt. But address passed to the dcbt,
> in GPR 9, doesn't contain anything close to the address displayed by mambo:
>
> systemsim % mysim cpu 0:0:0 display gpr 9
> 0x0000000000000240

What in the other GPRs?

> systemsim % mysim mcm 0 cpu 0 thread 0 dtranslate 0x240
> data address translation for 0x0000000000000240 failed
> systemsim %
>
> The dcbt instruction is in mm/slub.c; more context:
>
> 1241956         prefetch(object + s->offset);
> 1241957 c0000000003a2eb4:       20 00 3f 81     lwz     r9,32(r31)
> 1241958         if (unlikely(!x))
> 1241959 c0000000003a2eb8:       15 4a 3a 7d     add.    r9,r26,r9
> 1241960 c0000000003a2ebc:       08 00 82 41     beq     c0000000003a2ec4 <kmem_cache_alloc+0x114>
> 1241961         __asm__ __volatile__ ("dcbt 0,%0" : : "r" (x));
> 1241962 c0000000003a2ec0:       2c 4a 00 7c     dcbt    0,r9
> 1241963 c0000000003a2ec4:       00 00 00 60     nop
> 1241964 c0000000003a2ec8:       00 00 00 60     nop
>
> so probably from a prefetch_freepointer() in
> https://github.com/torvalds/linux/blob/master/mm/slub.c#L2815
>
>
> >> systemsim % c
> >> 145785082: (550674532): [    0.008506] smp: Brought up 2 nodes, 4 CPUs
> >> 145798101: (550687551): [    0.008527] numa: Node 0 CPUs: 0-1
> >> 145810514: (550799964): [    0.008551] numa: Node 1 CPUs: 2-3
> >
> > Does it still happen with a single CPU?
>
> It still happens with maxcpus=0 or =1. However if I disable radix passing
> disable_radix=1 to command line I'm able to boot.

What about with the number of threads configured in skiboot.tcl set to 1?

> Today I've built upstream mambo and the same issue happens. I'm clueless
> yet what's happening... so if you have additional things to try let
> me know. It might be an issue with Mambo P10 running on P8.

It's probably just a P10 mambo bug. Even if it's not they're more
likely to have an answer for you about what's going on. Anyway, I'll
hold off on merging this until people figure it out.