FTrace on MPC8xx

[Joakim Tjernlund]

Stefan Roese <ml at stefan-roese.de> wrote on 2011/04/14 17:59:30:
>
> Hi Joakim,
>
> On Wednesday 13 April 2011 17:38:03 Joakim Tjernlund wrote:
> > > > How big was the size to copy_tofrom_user()? Did it mange to copy
> > > > any bytes?
> > >
> > > The size in __copy_tofrom_user is 4. And its the first call in
> > > ftrace_modify_code() that fails directly. This works just fine on a
> > > PPC440EPx board.
> >
> > Since the size is only 4 it would not use dcbX anyway(I think).
> > Then is is probably called with the wrong addresses?
>
> No, addresses seem to be correct. I checked a bit further (I'm quite new to
> the MPC8xx MMU) and it seems that trying to modify the code (that's the
> destination address) via __copy_tofrom_user() fails on MPC8xx. Still not sure
> why this is the case. Perhaps an 8xx guru might chime in here. ;)
>
> BTW: I just noticed that enabling CONFIG_PIN_TLB seems to resolve this issue.
> With this option enabled, the dynamic code modification works just fine.
>
> Joakim, Scott? Any ideas on this?

hmm, I guess 8xx really maps kernel RO as RO :) Try
changing in pte-8xx.h:
 - #define _PAGE_KERNEL_RO	(_PAGE_SHARED)
 + #define _PAGE_KERNEL_RO	(_PAGE_RW |_PAGE_SHARED)