Re: [Xen-devel] [PATCH=v3 1/8] xen: arm: map memory as inner shareable.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-03-17 at 15:06 +0000, Julien Grall wrote:
> Hi Ian,
> 
> On 03/17/2014 02:53 PM, Ian Campbell wrote:
> > The inner shareable domain contains all SMP processors, including different
> > clusters (e.g. big.LITTLE). Therefore this is the correct thing to use for 
> > Xen
> > memory mappings. The outer shareable domain is for devices on busses which 
> > are
> > coherent and barrier-aware (e.g. AMBA4 AXI with ACE). While the system 
> > domain
> > is for things behind bridges which are not.
> > 
> > One wrinkle is that Normal memory with attributes Inner Non-cacheable, Outer
> > Non-cacheable (which we call BUFFERABLE) must be mapped Outer Shareable on 
> > ARM
> > v7. Therefore change the prototype of mfn_to_xen_entry to take the attribute
> > index so we can DTRT. On ARMv8 the sharability is ignored and considered to
> > always be Outer Shareable.
> > 
> > Don't adjust the barriers, flushes etc, those remain as they were (which is
> > more than is now required).  I'll change those in a later patch.
> > 
> > Many thanks to Leif for explaining the difference between Inner- and
> > Outer-Shareable in words of two or less syllables, I hope I've replicated 
> > that
> > explanation properly above!
> 
> Is there any reason to not modify VTCR_EL2?

Could do as a future cleanup but I wanted to get Xen's own mappings
sorted first.

Ian



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