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Re: [Xen-devel] PCI Pass-through in Xen ARM: Draft 4

On Fri, 14 Aug 2015, Jan Beulich wrote:
> >>> On 13.08.15 at 19:01, <ian.campbell@xxxxxxxxxx> wrote:
> > On Thu, 2015-08-13 at 09:29 -0600, Jan Beulich wrote:
> > 
> > A bunch of your questions seem to be about things which have been discussed
> > at length in previous postings, it's probably worth reviewing some of those
> > discussions.
> With the huge amount of mail to be read after returning from vacation
> I had hoped to avoid that, assuming that results of such discussion
> would (should) manifest themselves in the new draft i.e. I specifically
> avoided to join the tail of the draft 3 thread).
> >> Furthermore OSes can generally reassign BARs as they see fit (as
> >> long as the chosen addresses don't collide with anything else).
> > 
> > Not with PV pcifront/back based setups, the BARs are fixed then I believe,
> > even for x86/PV. That model is being followed on ARM too.
> I'm unaware of the mechanism to avoid such re-assignment in Linux;

They simply don't work. The code to reassign BARs has never been

> it's even less clear how you'd expect to suppress this in other guest
> OSes (Windows - afaik - being able to run on ARM certainly makes it
> a candidate guest, even if maybe this doesn't work today), namely
> such not having any pcifront. And I hope this design discussion isn't
> limiting itself to Linux guests.

We'll write down in the ABI documentation that BARs reassignments are
not supported.

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