Re: [Xen-devel] [PATCH 5/25] Xen/doc: Add Xen virtual IOMMU doc

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 06/07/17 07:20, Lan Tianyu wrote:
> On 2017年07月05日 21:25, Julien Grall wrote:
> > Furthermore, on ARM we would be able to create the vIOMMU but it would
> > be unusable. Indeed, IOMMU are only used to protect devices. But you
> > don't see any way to say "This device is protected by the IOMMU". Did I
> > miss anything?
> The "device protection" you mentioned is DMA protection, right?. It's
> one of IOMMU capabilities. IOMMU also provides interrupt remapping and
> SVM(Shared virtual memory). I see ARM side also is pushing SVM feature
> in KVM maillist for native support. Finally, it needs to support SVM in
> VM and so virtual IOMMU is necessary regardless of full-virtualized or
> PV IOMMU
>
> http://lists.infradead.org/pipermail/linux-arm-kernel/2017-March/491614.html
I don't think SVM is strictly necessary to do DMA protection in the 
guest. Not all IOMMUs on ARM are able to use this feature but you may 
still want to allow the guest using the IOMMU. Did I miss anything?
Cheers,

--
Julien Grall

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