KASAN debug kernel fails to boot at early stage when CONFIG_SMP=y is set (kernel 6.5-rc5, PowerMac G4 3,6)

[Christophe Leroy]

Le 18/08/2023 à 11:16, Erhard Furtner a écrit :
> On Fri, 18 Aug 2023 09:13:21 +1000
> Michael Ellerman <mpe at ellerman.id.au> wrote:
> 
>> Try just removing the call to btext_unmap() entirely and see how far it goes?
>>
>> cheers
> 
> Ok, I commented out btext_unmap() in MMU_init() and the freeze just happens before the "Linux version 6.5.0-rc6-PMacG4-dirty [...]"-line:
> 
> [    0.000000] printk: bootconsole [udbg0] enabled
> [    0.000000] Total memory = 2048MB; using 4096kB for hash table
> [    0.000000] mapin_ram:125
> [    0.000000] mmu_mapin_ram:169 0 30000000 1400000 2000000
> [    0.000000] __mmu_mapin_ram:146 0 1400000
> [    0.000000] __mmu_mapin_ram:155 1400000
> [    0.000000] __mmu_mapin_ram:146 1400000 30000000
> [    0.000000] __mmu_mapin_ram:155 20000000
> [    0.000000] __mapin_ram_chunk:107 20000000 30000000
> [    0.000000] __mapin_ram_chunk:117
> [    0.000000] mapin_ram:134
> [    0.000000] kasan_mmu_init:129
> [    0.000000] kasan_mmu_init:132 0
> [    0.000000] kasan_mmu_init:137
> [    0.000000] setup_kuap:23
> [    0.000000] setup_kuap:25
> [    0.000000] setup_kuap:30
> [    0.000000] setup_kuap:35
> [    0.000000] Activating Kernel Userspace Access Protection
> [    0.000000] setup_kuap:40
> [    0.000000] Activating Kernel Userspace Execution Prevention
> 
> I also tried a kernel without KUAP/KUEP getting this:
> 
> [    0.000000] printk: bootconsole [udbg0] enabled
> [    0.000000] Total memory = 2048MB; using 4096kB for hash table
> [    0.000000] mapin_ram:125
> [    0.000000] mmu_mapin_ram:169 0 30000000 1400000 2000000
> [    0.000000] __mmu_mapin_ram:146 0 1400000
> [    0.000000] __mmu_mapin_ram:155 1400000
> [    0.000000] __mmu_mapin_ram:146 1400000 30000000
> [    0.000000] __mmu_mapin_ram:155 20000000
> [    0.000000] __mapin_ram_chunk:107 20000000 30000000
> [    0.000000] __mapin_ram_chunk:117
> [    0.000000] mapin_ram:134
> [    0.000000] kasan_mmu_init:129
> [    0.000000] kasan_mmu_init:132 0
> [    0.000000] kasan_mmu_init:137
> 
> Here too the freeze just happens before the line "Linux version 6.5.0-rc6-PMacG4-dirty [...]" in dmesg.
> 
> Attached is (warm boot) dmesg without KUAP/KUEP.

I'm wondering if the problem is just linked to the kernel being built 
with CONFIG_SMP or if it is the actual startup of a secondary CPU that 
cause the freeze.

Please leave the btext_unmap() in place because I think it is important 
to keep it, and start the kernel with the following parameter:

nr_cpus=1


Thanks
Christophe