Re: [V2 PATCH 0/9] x86/hvm: pkeys, add memory protection-key support

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 27/11/15 16:22, Han, Huaitong wrote:
> On Fri, 2015-11-27 at 12:59 +0000, Andrew Cooper wrote:
>> Just for my own understand, do you have a sample use-case for
>> protection
>> keys?
>>
>> As everything can WRPKRU, I cant see how it would actually be useful.
>> Clearly there is a usecase or you (Intel) wouldn't have gone to the
>> effort of putting into silicon.
>>
>> ~Andrew
> I understand PKU is a active memory protection, pkru register is thread
> -private, every thread can only change its pkru value, it is a
> enhancement of pte write/access, it provides two advantage:
> 1.During permission changes, we only need update pkru register instead 
>   of pte, so it can reduce the need to perform TLB shootdowns.
> 2.Compared with traditional read and write permissions, it can provide
> thread-private permissions.

So it is a feature which allows threads to cooperatively prevent
themselves trampling on each other.

I can see this being useful for debugging and robustness.

~Andrew