Subject: Re: 3.5+: yaboot, Invalid memory access

From: Benjamin Herrenschmidt <[email-masked]>
Date: Wed, 05 Sep 2012 11:08:28 +1000

On Tue, 2012-09-04 at 02:32 -0700, Christian Kujau wrote:
> On Tue, 4 Sep 2012 at 16:51, Michael Ellerman wrote:
> > My guess would be we're calling that quite early and the __put_user()
> > check is getting confused and failing. That means we'll have left some
> > code unpatched, which then fails.
> > 
> > Can you try with the patch applied, but instead of returning if the
> > __put_user() fails, just continue on anyway.
> 
> You mean, like this?

Try this:

powerpc: Don't use __put_user() in patch_instruction

patch_instruction() can be called very early on ppc32, when the kernel
isn't yet running at it's linked address. That can cause the !
is_kernel_addr() test in __put_user() to trip and call might_sleep()
which is very bad at that point during boot.

Use a lower level function instead for now, at least until we get to
rework ppc32 boot process to do the code patching later, like ppc64
does.

Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
---

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index dd223b3..17e5b23 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -20,7 +20,7 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
 {
 	int err;
 
-	err = __put_user(instr, addr);
+	__put_user_size(instr, addr, 4, err);
 	if (err)
 		return err;
 	asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));