Re: [Xen-devel] PCI Passthrough ARM Design : Draft1

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Jun 26, 2015 at 01:41:08PM +0100, Ian Campbell wrote:
> On Fri, 2015-06-26 at 17:27 +0530, Manish Jaggi wrote:
> 
> > I still need to implement a domctl xc_domain_query_memory_mapping. If 
> > reserve a memory of
> > GUEST_MMIO_HOLE_SIZE from GUEST_MMIO_HOLE_ADDR in arch-arm.h xl tools 
> > need some
> > way to query which range is allocated and which is free in this hole.
> 
> If it needs this info after the fact then it should stash it somewhere
> itself, no need for a hypercall to get it back from Xen.
> 
> You may even be able to use the pciback xenstore nodes which you'll have
> added anyway, otherwise something specific under the /libxl namespace
> would seem like the way to go. 

Xenstore keys would be the easiest in Xen PCIback.


Keep also in mind that PCI devices MMIO regions can be huge. If you say
pass in 64 NICs - each with 128MB MMIO region - you got quite a large
of MMIO area.

I would advocate a more dynamic idea of GUEST_MMIO_* so that the toolstack
can allocate those with headroom. Perhaps stash it at the far far end
of the guest accessible memory? But that would require an 64-bit capable
OS which might not work for all use-cases (where you want a 32-bit OS).

> 
> Ian.
> 
> 
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