Re: [PATCH 01/10] xen: arm: map memory as inner shareable.

[Ian Campbell <Ian.Campbell@citrix.com>]

On Tue, 2013-07-02 at 16:09 +0200, Leif Lindholm wrote:
> On Fri, Jun 28, 2013 at 05:10:47PM +0100, 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
> > barriers (e.g. AMBA4).
> 
> I think this should say something like "which are coherent and
> barrier-aware".
> 
> And to be technically correct, the example should say "AMBA4 AXI with
> ACE").
> 
> > While the system domain is for things behind bridges > which do not.
>  
> And given the above ... -> 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.
> > 
> > While I'm here change all the dmb/dsb with an implicit sy to an explicit sy,
> > to make future changes simpler. Other than that 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!
>  
> Apart from my usual nitpicking, indeed :)

Thanks, I was sure I was playing a bit fast and loose with the
specifics!

> [...]
> > +    switch ( attr )
> > +    {
> > +    case BUFFERABLE:
> > +        /*
> > +         * ARM ARM: Overlaying the shareability attribute (B3-1376 to 1377)
> 
> It would be worth to indicate the revision of the ARM ARM here (in this
> instance DDI 0406C.b).

Good idea, thanks.

Ian.