[PATCH] powerpc/kasan/book3s_64: warn when running with hash MMU

[Nathan Lynch]

Michael Ellerman <mpe at ellerman.id.au> writes:
> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
>> + KASAN list
>>
>> Le 06/10/2022 à 06:10, Michael Ellerman a écrit :
>>> Nathan Lynch <nathanl at linux.ibm.com> writes:
>>>> kasan is known to crash at boot on book3s_64 with non-radix MMU. As
>>>> noted in commit 41b7a347bf14 ("powerpc: Book3S 64-bit outline-only
>>>> KASAN support"):
>>>>
>>>>    A kernel with CONFIG_KASAN=y will crash during boot on a machine
>>>>    using HPT translation because not all the entry points to the
>>>>    generic KASAN code are protected with a call to kasan_arch_is_ready().
>>> 
>>> I guess I thought there was some plan to fix that.
>>
>> I was thinking the same.
>>
>> Do we have a list of the said entry points to the generic code that are 
>> lacking a call to kasan_arch_is_ready() ?
>>
>> Typically, the BUG dump below shows that kasan_byte_accessible() is 
>> lacking the check. It should be straight forward to add 
>> kasan_arch_is_ready() check to kasan_byte_accessible(), shouldn't it ?
>
> Yes :)
>
> And one other spot, but the patch below boots OK for me. I'll leave it
> running for a while just in case there's a path I've missed.

It works for me too, thanks (p8 pseries qemu).

This avoids the boot-time oops, but kasan remains unimplemented for hash
mmu. Raising the question: with the trivial crashes addressed, is the
current message ('KASAN not enabled as it requires radix!') sufficient
to notify developers (such as me, a week ago) who mean to use kasan on a
book3s platform, unaware that it's radix-only? Would a WARN or something
more prominent still be justified?

I guess people will figure it out as soon as they think to search the
kernel log for 'KASAN'...