Re: [PATCH] arm64: mm: Move KPTI helpers to mmu.c

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 11/09/2025 11:19, Ard Biesheuvel wrote:
>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
>> index 49f1a810df16..624edd6c4964 100644
>> --- a/arch/arm64/include/asm/mmu.h
>> +++ b/arch/arm64/include/asm/mmu.h
>> @@ -104,5 +104,11 @@ static inline bool kaslr_requires_kpti(void)
>>         return true;
>>  }
>>
>> +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
>> +void kpti_install_ng_mappings(void);
>> +#else
>> +static inline void kpti_install_ng_mappings(void) {}
>> +#endif
>> +
> Nit: you might just keep the former declaration, and check for
> IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) in the function, rather than
> propagating this distinction to the header file.
> But either is fine with me.

That's an option, but that would mean removing the #ifdef around the
functions defined in mmu.c. They would probably get eliminated by the
linker if the CONFIG isn't defined, but I'm not so sure about the static
variable (kpti_ng_temp_alloc). Probably not a big deal but I feel
keeping the #ifdef is more self-documenting as well.

- Kevin