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 13:20 +0800, Huaitong Han wrote:
> 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.
A thread may have many memeroy zones that has different permissions
too.
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