Re: [Xen-devel] One question about the hypercall to translate gfn to mfn.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.12.14 at 08:24, <kevin.tian@xxxxxxxxx> wrote:
> - is there existing _map_ call for this purpose per your knowledge, or
> a new one is required? If the latter, what's the additional logic to be
> implemented there?

I think the answer to this depends on whether you want to use
grants. The goal of using the native driver in the guest (mentioned
further down) speaks against this, in which case I don't think we
have an existing interface.

> - when you say _map_, do you expect this mapped into dom0's virtual
> address space, or just guest physical space?

Iiuc you don't care about the memory to be visible to the CPU, all
you need is it being translated by the IOMMU. In which case the
input address space for the IOMMU (which is different between PV
and PVH) is where this needs to be mapped into.

> - how is BFN or unused address (what do you mean by address here?)
> allocated? does it need present in guest physical memory at boot time,
> or just finding some holes?

Fitting this into holes should be fine.

> - graphics memory size could be large. starting from BDW, there'll
> be 64bit page table format. Do you see any limitation here on finding
> BFN or address?

I don't think this concern differs much for the different models: As long
as you don't want the same underlying memory to be accessible by
more than one guest, the address space requirements ought to be the
same.

Jan


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