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

[Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>]

On 09/12/14 10:37, Yu, Zhang wrote:
> 
> 
> On 12/9/2014 6:19 PM, Paul Durrant wrote:
>> I think use of an raw mfn value currently works only because dom0 is
>> using a 1:1 IOMMU mapping scheme. Is my understanding correct, or do
>> you really need raw mfn values?
> Thanks for your quick response, Paul.
> Well, not exactly for this case. :)
> In XenGT, our need to translate gfn to mfn is for GPU's page table,
> which contains the translation between graphic address and the memory
> address. This page table is maintained by GPU drivers, and our service
> domain need to have a method to translate the guest physical addresses
> written by the vGPU into host physical ones.
> We do not use IOMMU in XenGT and therefore this translation may not
> necessarily be a 1:1 mapping.

XenGT must use the IOMMU mappings that Xen has setup for the domain
which owns the GPU. Currently Dom0 own's the GPU and so it's IOMMU
mappings match the MFN's addresses. I suspect XenGT will not work if Xen
is booted with iommu=dom0-strict.

Malcolm

> 
> B.R.
> Yu
> 
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