Re: [Xen-devel] Xen ARM smmu questions

[Julien Grall <julien.grall@xxxxxxx>]

On 3/12/19 8:58 AM, jinchen wrote:
> Hello xen-devel,
Hello,

> I'm reading the code of xen arm smmu in drivers/passthrough/arm, and I 
> have some questions that confused me.
> I think if the board use SMMU, xen will take charge of it before dom0 
> boot, and will not pass the node of SMMU to dom0 in device tree,
> so my question is how dom0 use SMMU? or can dom0 use SMMU? What dom0 use 
> if it wants to use IOMMU?
> What about domU? The SMMU could be passed to domU?
Some SMMU are able to provide Stage 1 (Guest VA to Guest PA) and Stage 2 
(Guest PA to Host PA) support. In the current configuration, Xen will 
use the Stage 2 part to isolate device passthrough. Stage 1 is not 
supported.
If you wanted a guest to use the SMMU, you would either need to provide 
Stage 1 support (requires HW support) or a PV IOMMU.
Alternatively, you might be able to give the SMMU to Dom0. I haven't 
explored it so far. Do you have a use case for using the IOMMU in guest?
Cheers,

--
Julien Grall

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