Subject: [Bug 215621] Warning: Unable to mark rodata read only on this CPU. (PPC970MP)

From: [email-masked]
Date: Sun, 20 Feb 2022 16:38:59 +0000

https://bugzilla.kernel.org/show_bug.cgi?id=215621

Christophe Leroy ([email-masked]) changed:

           What    |Removed                     |Added
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                 CC|                            [email-masked]

--- Comment #2 from Christophe Leroy ([email-masked]) ---
Look at
https://elixir.bootlin.com/linux/v5.17-rc4/source/arch/powerpc/kernel/cputable.c#L196
at you'll see that your processor has .mmu_features = MMU_FTRS_PPC970

Then you see at
https://elixir.bootlin.com/linux/v5.17-rc4/source/arch/powerpc/include/asm/mmu.h#L135
that MMU_FTRS_PPC970 doesn't include MMU_FTR_KERNEL_RO.

MMU_FTR_KERNEL_RO is in POWER6.

In commit 984d7a1ec67c ("powerpc/mm: Fixup kernel read only mapping") you see
that this feature appears in ISA 2.04.

Previous version of ISA only has PP bits which only provides RW for kernel
pages.

So this bug is not a bug, it's a limitation of PPC970MP, and the warning in
dmesg is there to warn you that allthough you have select
CONFIG_STRICT_KERNEL_RWX, this CPU doesn't support it.

And for the same reason, CONFIG_STRICT_MODULE_RWX doesn't work either.

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