Re: [PATCH v4 1/3] arch/x86: Update config and kernel doc for MPK feature on AMD

[Babu Moger]

On 5/13/20 10:09 AM, Dave Hansen wrote:
> On 5/12/20 4:58 PM, Babu Moger wrote:
>> +config X86_MEMORY_PROTECTION_KEYS
>> +	# Both Intel and AMD platforms support "Memory Protection Keys"
>> +	# feature. So add a generic option X86_MEMORY_PROTECTION_KEYS
>> +	# and set the option whenever X86_INTEL_MEMORY_PROTECTION_KEYS
>> +	# is set. This is to avoid the confusion about the feature
>> +	# availability on AMD platforms. Also renaming the old option
>> +	# would cause the user an extra prompt during the kernel
>> +	# configuration. So avoided changing the old config name.
>> +	def_bool X86_INTEL_MEMORY_PROTECTION_KEYS
> 
> Hi Babu,
> 
> I made a request earlier for an end date (or version) to be included
> here.  I believe that appeared in one of your earlier versions, but it
> was removed in later ones.
> 
> Was there a reason for that?

Dave, Sorry, I misunderstood that. I thought we probably are not going to
change the sources/makefile(ifdefs mostly) as it was technically not
required. Now I am reading that we are going to change that in the future
and just keep X86_MEMORY_PROTECTION_KEYS going forward.
Sure. I will add the text you proposed. Please feel free to correct again.

> 
> I'd really prefer to put some kind of expiration date on the config
> option.  It will outlive us all otherwise.
> 
>>  Memory Protection Keys for Userspace (PKU aka PKEYs) is a feature
>>  which is found on Intel's Skylake "Scalable Processor" Server CPUs.
>> -It will be avalable in future non-server parts.
>> +It will be available in future non-server parts. Also, AMD64
>> +Architecture Programmerâs Manual defines PKU feature in AMD processors.
> 
> I actually worked pretty hard to make that sentence useful to Linux
> users.  Instead of forcing them to imply that it will be available on
> future AMD CPUs, can we just come out and say it?  Can we give any more
> information to our users?
> 
> Naming the AMD manual in which the feature is defined doesn't really
> help our users.  Let's not waste the bytes on it.
> 
> How about:
> 
> 	Memory Protection Keys for Userspace (PKU aka PKEYs) is a
> 	feature which is found on Intel's Skylake (and later) "Scalable
> 	Processor" Server CPUs.  It will be avalable in future non-
> 	server Intel parts and future AMD parts.

This should be good enough. Thanks.
> 
> Any clarity you can add, such as to say what AMD is doing for server vs.
> client  would be nice.
> 
> BTW, when I first submitted pkeys, I didn't have any statement like this
> in the changelog or documentation.  Ingo, I think, asked for it and I
> worked with folks inside Intel to figure out how much we could say
> publicly about our plans.  A similar effort from AMD would be much
> appreciated here.
>