Re: [Xen-devel] [PATCH V9 0/5] x86/hvm: pkeys, add memory protection-key support

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Huaitong Han
> Sent: Wednesday, February 03, 2016 10:12 PM
> 
> The PKRU register (protection key rights for user pages) is a 32-bit register
> with the following format: for each i (0 â i â 15), PKRU[2i] is the
> access-disable bit for protection key i (ADi); PKRU[2i+1] is the write-disable
> bit for protection key i (WDi).
> 

Curious about protection key usage here. There are 16 PKRU indexes, but
each is associated only with 2 bits which means 4 possible combinations. Does
it mean in reality OS will only use 4 indexes now (might extend to 16 if
permission bits are extended to say 4bits in the future)?

Thanks
Kevin
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