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

["Han, Huaitong" <huaitong.han@xxxxxxxxx>]

On Thu, 2016-02-04 at 04:56 +0000, Tian, Kevin wrote:
> > 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)?
No, 4 indexs cannot finish thread-private permission job: the index
value is from page table entry, cannot be changed with different
threads.
The Memory access process with PKEYS feature: the thread get pkey value
from page table entry, pkey value is the index to PKRU(thread-self)
domain, and get ADi/WDi via RDPKRU.

> 
> Thanks
> Kevin
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