Re: [PATCH v2 1/2] powerpc/ps3: Change updateboltedpp panic to info

[Geoff Levand <geoff@infradead.org>]

Hi,

On 1/15/23 16:06, Michael Ellerman wrote:
> Geoff Levand <geoff@infradead.org> writes:
>> On 1/9/23 09:41, Christophe Leroy wrote:
>>>
>>>
>>> Le 03/01/2023 à 18:51, Geoff Levand a écrit :
>>>> Commit fdacae8a84024474afff234bdd1dbe19ad597a10 (powerpc: Activate
>>>> CONFIG_STRICT_KERNEL_RWX by default) causes ps3_hpte_updateboltedpp()
>>>> to be called.  Change the panic statment in ps3_hpte_updateboltedpp()
>>>> to a pr_info statement so that bootup can continue.
>>>
>>> But if I understand correctly, it means that CONFIG_STRICT_KERNEL_RWX 
>>> won't work then.
>>>
>>> So, shouldn't we keep the panic and forbid CONFIG_STRICT_KERNEL_RWX on PS3 ?
>>
>> mmu_hash_ops.updateboltedpp returns void, so I can't return an error code to
>> indicate the feature is not supported.
> 
> We could change that in the medium term.
> 
>> I could do something like this in arch/powerpc/Kconfig:
>>
>> -       select ARCH_HAS_STRICT_KERNEL_RWX       if (PPC_BOOK3S || PPC_8xx || 40x) && !HIBERNATION
>> +       select ARCH_HAS_STRICT_KERNEL_RWX       if (PPC_BOOK3S || PPC_8xx || 40x) && !PPC_PS3 && !HIBERNATION
>>
>> But then the ppc64_defconfig would be built without STRICT_KERNEL_RWX.
> 
> Yeah that would be a pity.
> 
> We could do the above and disable PS3 in ppc64_defconfig, allowing
> ppc64_defconfig to still have STRICT_KERNEL_RWX.

I really want to keep PS3 included in ppc64_defconfig.  Not that I expect
anyone to boot a ppc64_defconfig kernel on PS3, but that is one of the
'standard' configs that is built by some automated builders, and generally by
anyone doing changes to the powerpc arch, and I want to keep getting those
build tests for PS3.

> I assume actual PS3 users would use a ps3_defconfig anyway right?

Yeah, a derivative of it.  They are most likely are using 'Jailbreak' firmware
that allows them to run Linux in the gameos partition.

> Relatedly are there any actual PS3 users left? ;)

It seems there are more users now than a few years ago.  I think they buy PS5s
to play the latest games, and use their old console to mess around with Linux.
I generally get a private inquiry every 3 or 4 weeks.  Usually asking how to
update their kernel, or how to install a modern distro.

>> What other 'clean' way is there?
> 
> If we want to have a multi-platform kernel image that can boot on PS3
> and other platforms, and have strict kernel RWX, then we need some
> runtime logic to deal with that.
> 
> I'd rather not do that though, because it adds complexity to deal with a
> pretty obscure corner case, and I suspect no one really boots a
> ppc64_defconfig on actual PS3 hardware these days.
> 
> So my preference is we disable PS3 in ppc64_defconfig, and make PS3
> incompatible with STRICT_KERNEL_RWX.

As mentioned, I'd really like to keep PS3 included in ppc64_defconfig.  My
original patch that basically just ignores the call to
mmu_hash_ops.updateboltedpp allows that, and I haven't experienced any problems
with it yet.

My preference would be to keep PS3 in ppc64_defconfig, and either apply my
original patch, or I keep that patch in my ps3-linux repo on kernel.org. Then,
if we end up adding runtime support for RWX I then fixup PS3 to use that.

-Geoff