Re: [PATCH v1 03/13] powerpc/mm/32s: rework mmu_mapin_ram()

[Christophe Leroy]

Le 18/12/2018 à 15:55, Christophe Leroy a écrit :
> Le 18/12/2018 à 15:15, Christophe Leroy a écrit :
> > Le 18/12/2018 à 15:07, Jonathan Neuschäfer a écrit :
> > > On Tue, Dec 18, 2018 at 09:18:42AM +0000, Christophe Leroy wrote:
> > > > The only difference I see then are the flags. Everything else is seems
> > > > identical.
> > > >
> > > > I know you tried already, but would you mind trying once more with the
> > > > following change ?
> > > [...]
> > > > -        setbat(idx, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
> > > > +        setbat(idx, PAGE_OFFSET + base, base, size, PAGE_KERNEL_X);
> > >
> > > Good call, with this workaround on top of patches 1-3, it boots again:
> > >
> > >     # mount -t debugfs d /sys/kernel/debug
> > >     # cat /sys/kernel/debug/powerpc/block_address_translation
> > >     ---[ Instruction Block Address Translation ]---
> > >     0: 0xc0000000-0xc0ffffff 0x00000000 Kernel EXEC
> > >     1:         -
> > >     2: 0xc1000000-0xc17fffff 0x01000000 Kernel EXEC
> > >     3:         -
> > >     4: 0xd0000000-0xd1ffffff 0x10000000 Kernel EXEC
> > >     5:         -
> > >     6:         -
> > >     7:         -
> > >
> > >     ---[ Data Block Address Translation ]---
> > >     0: 0xc0000000-0xc0ffffff 0x00000000 Kernel RW
> > >     1: 0xfffe0000-0xffffffff 0x0d000000 Kernel RW no cache guarded
> > >     2: 0xc1000000-0xc17fffff 0x01000000 Kernel RW
> > >     3:         -
> > >     4: 0xd0000000-0xd1ffffff 0x10000000 Kernel RW
> > >     5:         -
> > >     6:         -
> > >     7:         -
> > >
> > > > I think we may have some code trying to modify the kernel text 
> > > > without using
> > > > code patching functions.
> > >
> > > Is there any faster way than to sprinkle some printks in setup_kernel
> > > and try to find the guilty piece of code this way?
> >
> > Can you start with the serie 
> > https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=75072 ?
>
> Ok, the thing I was thinking about was the MMU_init_hw() but it is 
> called before mapin_ram() so it should not be a problem. Not sure that 
> serie improves anything at all here.
>
> So there must be something else, pretty early (before the system is able 
> to properly handle and display an Oops for write to RO area.)
>
> Does anybody have an idea of what it can be ?


Stupid of me. In fact at the time being, BATS cover both RO and RW data 
areas, so it can definitly not be mapped with PAGE_KERNEL_ROX.

In fact, as I have CONFIG_BDI_SWITCH in my setup, PAGE_KERNEL_TEXT is 
PAGE_KERNEL_X on my side. That's the reason why I missed it.

With this change being done to patch 3, does the overall serie works for 
you ?

Thanks
Christophe



> Christophe
>
> > Christophe
> >
> > > Jonathan