Re: [Xen-devel] [RFC PATCH 9/9] xen: Add use_iommu flag to createdomain domctl

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Oleksandr Tyshchenko writes ("Re: [RFC PATCH 9/9] xen: Add use_iommu flag to 
createdomain domctl"):
> On Tue, Apr 25, 2017 at 6:23 PM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> > Let me explain where I'm coming from:
> >
> > 1. if not populating the iommu page table causes Xen to malfunction
> >    (crash?), it is a bug. It should be fixed without involvement
> >    from toolstack.
> > 2. if this is an optimasation, can't we not always populate iommu pt
> >    hence no new flag is needed?
> >
> > Overall I'm not too convinced a new flag is needed.
>
> We don't want to always populate IOMMU page table since it might be
> just wasting CPU and memory resources if no devices are assigned to
> domain. That's why we need this hint.

I thought we already had a way to tell libxl that pci passthrough is
expected for this domain.  There are other things that want to know
this in advance.  I can't seem to find it now at least in the docs,
though.

Ian.

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