Subject: Re: [PATCH] powerpc: Fix alignment of secondary cpu spin vars

From: Olof Johansson <[email-masked]>
Date: Wed, 8 Jan 2014 09:48:28 -0800

On Wed, Jan 08, 2014 at 03:18:26PM +1100, Benjamin Herrenschmidt wrote:
> On Wed, 2014-01-08 at 15:09 +1100, Michael Ellerman wrote:
> > > Of course, main worry is that this is just hiding some latent NULL
> > deref in
> > > the kernel now... :-/
> > 
> > Wow, that would have to come close to winning the
> > grossest-hack-in-arch-powerpc
> > award :)
> > 
> > Have you tried changing the value at 8 to point to a reserved page?
> > 
> > Some other possibilities:
> > 
> >  * Change the #define so FIXUP_ENDIAN is empty for PASEMI, that would
> > mean
> >    you'd only be able to boot pasemi_defconfig.

No thanks -- this went uncaught because that used to be all I booted
(and for some random reason it didn't trigger in that case).

> >  * Move the hack into FIXUP_ENDIAN
> 
> We actually found the root cause on irc the other day, I was waiting for
> Olof to send a fix :-)

Yeah, I'm low on spare time these days, in particular spare time to spend on
ppc stuff. :-(

> Olof: Can you try this totally untested patch ?

With one fixup below:

Tested-by: Olof Johansson <[email-masked]>

> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -1986,8 +1986,6 @@ static void __init prom_init_stdout(void)
>         /* Get the full OF pathname of the stdout device */
>         memset(path, 0, 256);
>         call_prom("instance-to-path", 3, 1, prom.stdout, path, 255);
> -       stdout_node = call_prom("instance-to-package", 1, 1, prom.stdout);
> -       val = cpu_to_be32(stdout_node);
>         prom_setprop(prom.chosen, "/chosen", "linux,stdout-package",
>                      &val, sizeof(val));
>         prom_printf("OF stdout device is: %s\n", of_stdout_device);
> @@ -1995,10 +1993,14 @@ static void __init prom_init_stdout(void)
>                      path, strlen(path) + 1);
>  
>         /* If it's a display, note it */
> -       memset(type, 0, sizeof(type));
> -       prom_getprop(stdout_node, "device_type", type, sizeof(type));
> -       if (strcmp(type, "display") == 0)
> -               prom_setprop(stdout_node, path, "linux,boot-display", NULL, 0);
> +       stdout_node = call_prom("instance-to-package", 1, 1, prom.stdout);
> +       if (stdout_node != PROM_ERROR) {
> +               val = cpu_to_be32(stdout_node);
> +               memset(type, 0, sizeof(type));
> +               prom_getprop(stdout_node, "device_type", type, sizeof(type));
> +               if (strcmp(type, "display") == 0)
> +                       prom_setprop(stdout_node, path, "linux,boot-display", NU

Line is cut off, this needs "NULL, 0);" at the end.

-Olof