Le 13/08/2023 à 21:38, Erhard Furtner a écrit :
> On Fri, 11 Aug 2023 06:45:14 +0000
> Christophe Leroy <christophe.le...@csgroup.eu> wrote:
>
>> Le 11/08/2023 à 01:48, Erhard Furtner a écrit :
>>> I wanted to fire up my PowerMac G4 MDD (Dual CPU) with a KASAN debug build
>>> of kernel 6.5-rc5 for testing purposes. But the kernel fails to boot at a
>>> very early stage. I only get a white screen reading
>>> "done
>>> found display: /pci@f0000000/ATY,AlteracParent@10/ATY,Alterac_B@1,
>>> opening..."
>>
>> Can you try with CONFIG_PPC_EARLY_DEBUG and see if you get more
>> information on the screen ?
>
> With CONFIG_PPC_EARLY_DEBUG set booting continues and I get two more lines on
> a white screen:
>
> [ 0.000000] printk: bootconsole [udbg0] enabled
> [ 0.000000] Total memory = 2048MB; using 4096kB for hash table
>
> Afterwards the G4 freezes.
Interesting. That means we get stuck somewhere around MMU_init()
We know that MMU_init_hw() is called and runs at least until:
pr_info("Total memory = %lldMB; using %ldkB for hash table\n",
(unsigned long long)(total_memory >> 20), Hash_size >> 10);
But we never reach the print in setup_kuap() which is itself called by
set_kup():
pr_info("Activating Kernel Userspace Access Protection\n");
Could you try to narrow more the issue by spreading pr_info() at places
in the code below and/or the called functions ? Either we never come
back from MMU_init_hw(), or one of mapin_ram() btext_unmap()
kasan_mmu_init() fails.
So the piece of code we are interested in is located in
arch/powerpc/mm/init_32.c and is:
/* Initialize the MMU hardware */
if (ppc_md.progress)
ppc_md.progress("MMU:hw init", 0x300);
==> MMU_init_hw();
/* Map in all of RAM starting at KERNELBASE */
if (ppc_md.progress)
ppc_md.progress("MMU:mapin", 0x301);
mapin_ram();
/* Initialize early top-down ioremap allocator */
ioremap_bot = IOREMAP_TOP;
if (ppc_md.progress)
ppc_md.progress("MMU:exit", 0x211);
/* From now on, btext is no longer BAT mapped if it was at all */
#ifdef CONFIG_BOOTX_TEXT
btext_unmap();
#endif
kasan_mmu_init();
==> setup_kup();
Christophe
>
> By chane I found out another interesting thing: This only happens on cold
> boots.
>
> If I boot the G4 up with another kernel first and boot the SMP KASAN kernel
> afterwards it just boots up fine too! On further reboots the SMP KASAN kernel
> keeps booting up normally. Until I turn the machine off - and next time I
> turn it on the same SMP KASAN kernel fails booting again as described.
> Strange...
>
> This behaviour however is reproducible. Tried that procedure 15-20 times just
> to be sure. Hope you can make something out of it.
>
> Attached is a dmesg of a successful SMP KASAM kernel boot attempt when a
> working kernel was booted first.
>
> Regards,
> Erhard F.
