Re: [PATCH RFC v9 02/25] set_memory: Introduce set_memory_pkey() stub

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

On 01/09/2026 16:33, Linu Cherian wrote:
> Kevin,
>
> On Tue, Aug 18, 2026 at 03:08:44PM +0100, Kevin Brodsky wrote:
>> Introduce a new function, set_memory_pkey(), which sets the
>> protection key (pkey) of pages in the specified linear mapping
>> range. Architectures implementing kernel pkeys (kpkeys) must
>> provide a suitable implementation; an empty stub is added as
> Could you make it explicit here why we are restricting this only
> to the linear mapping range ? Would be helpful to add the reasoning
> in the commit message and as comments.
>
> Essentially we are also making a assumption here that there are no
> aliases to the linear map ?

We're not assuming this, this function is called on pages that are also
mapped as part of the kernel image. But indeed it ignores aliases,
unlike e.g. set_memory_ro(). Really its name is wrong as discussed below.

>> fallback.
>>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> ---
>>  include/linux/set_memory.h | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
>> index 3030d9245f5a..7b3a8bfde3c6 100644
>> --- a/include/linux/set_memory.h
>> +++ b/include/linux/set_memory.h
>> @@ -84,4 +84,11 @@ static inline int set_memory_decrypted(unsigned long addr, int numpages)
>>  }
>>  #endif /* CONFIG_ARCH_HAS_MEM_ENCRYPT */
>>  
>> +#ifndef CONFIG_ARCH_HAS_KPKEYS
>> +static inline int set_memory_pkey(unsigned long addr, int numpages, int pkey)
>> +{
>> +	return 0;
>> +}
>> +#endif
> Would be better to make this (linar map range)constraint on the API name or that passed
> as a boolean flag ?

Indeed, in fact I've been thinking about renaming this function for a
while and I've already done it locally :) It'll be set_direct_map_pkey()
in the next version.

> Also, it would be better to have the __is_lm_address checks in this generic wrapper which
> then calls arch_set_memory_pkey ?

That's not unreasonable, but such pattern isn't used by other functions
in set_memory.h and I'd rather not deviate too much without a good reason.

- Kevin