Re: [BISECTED] kexec regression on PowerBook G4

[Aaro Koskinen <aaro.koskinen@iki.fi>]

Hi,

On Wed, May 22, 2019 at 08:14:23AM +0200, Christophe Leroy wrote:
> Le 22/05/2019 à 00:18, Aaro Koskinen a écrit :
> >I was trying to upgrade from v5.0 -> v5.1 on PowerBook G4, but when trying
> >to kexec a kernel the system gets stuck (no errors seen on the console).
> 
> Do you mean you are trying to kexec a v5.1 kernel from a v5.0 kernel, or do
> you have a working v5.1 kernel, but kexec doesn't work with it ?

To summarize, my system's boot goes like this:

Open Firmware -> kernel A (small due to OF limit) -> (kexec) -> kernel B (big)

First both A & B were at v5.0 ==> boot works.
Then I upgraded B to v5.1 ==> boot works.
Then I upgraded A to v5.1 ==> boot fails.

So the issue must be in A. So after bisecting I got the following result:

	Kernel A with commit 93c4a162b014 ==> fails
	Kernel A with commit 93c4a162b014^1 ==> works

n >Bisected to: 93c4a162b014 ("powerpc/6xx: Store PGDIR physical address
> >in a SPRG"). This commit doesn't revert cleanly anymore but I tested
> >that the one before works OK.
> 
> Not sure that's the problem. There was a problem with that commit, but it
> was fixed by 4622a2d43101 ("powerpc/6xx: fix setup and use of
> SPRN_SPRG_PGDIR for hash32").
> You probably hit some commit between those two during bisect, that's likely
> the reason why you ended here.
> 
> Can you restart your bisect from 4622a2d43101 ?

This is not a good commit to start with, as it already gives "kernel
tried to execute exec protected page..." after the "Bye!" message.

> If you have CONFIG_SMP, maybe you should also consider taking 397d2300b08c
> ("powerpc/32s: fix flush_hash_pages() on SMP"). Stable 5.1.4 includes it.

This is UP computer and CONFIG_SMP is not set.

> >With current Linus HEAD (9c7db5004280), it gets a bit further but still
> >doesn't work: now I get an error on the console after kexec "Starting
> >new kernel! ... Bye!":
> >
> >	kernel tried to execute exec-protected page (...) - exploit attempt?
> 
> Interesting.
> 
> Do you have CONFIG_STRICT_KERNEL_RWX=y in your .config ? If so, can you
> retry without it ?

I don't set that option.

A.