[Xen-devel] [PATCH for-4.5 v2 0/8] xen: arm: map normal memory as inner shareable, reduce scope of various barriers

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

Currently Xen maps all RAM as Outer-Shareable, since that seemed like
the most conservative option early on when we didn't really know what
Inner- vs. Outer-Shareable meant. However we have long suspected that
actually Inner-Shareable would be the correct type to use.

After reading the docs many times, getting more confused each time, I
finally got a reasonable explanation from a man (and a dog) down the
pub: Inner-Shareable == the processors in an SMP system, while
Outer-Shareable == devices. (NB: Not a random man, he knew what he was
talking about...). With that in mind switch all of Xen's memory mapping,
page table walks and an appropriate subset of the barriers to be inner
shareable.

In addition I have switched barriers to use the correct read/write/any
variants for their types. Note that I have only tackled the generic
mb/rmb/wmb and smp_* barriers (mainly used by common code) here. There
are also quite a few open-coded full-system dsb's in the arch code which
I will look at another time.

v1 of this was back in June[0], and I deferred it due to the 4.3 freeze,
so given that we are now frozen for 4.4 this is clearly 4.5 material.

I've slightly forgotten what was changed since then, but apart from
rebasing the highlights are:

      * dropped all the bogus tlb flush stuff, which was wrong, or at
        best confused.
      * mfn_to_p2m_entry sets shareability based on mattr, dev mappings
        remain outer
      * some clarifications to the comments.

[0] http://lists.xen.org/archives/html/xen-devel/2013-06/msg02969.html


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