[Xen-devel] [PATCH v3 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.

Since v2 I have just rebased onto current staging. All except the first
patch have an ack attached already.

Ian.


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