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xen-devel
[Xen-devel] Re: [XEN-IOMMU] Proposal of DMA protection/isolation support
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To: |
"Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [XEN-IOMMU] Proposal of DMA protection/isolation support |
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From: |
"Wei Wang2" <wei.wang2@xxxxxxx> |
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Date: |
Wed, 16 Jan 2008 18:15:53 +0100 |
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Cc: |
muli@xxxxxxxxxx, "Dannowski, Uwe" <Uwe.Dannowski@xxxxxxx>, "Hohmuth, Michael" <Michael.Hohmuth@xxxxxxx>, "Woller, Thomas" <thomas.woller@xxxxxxx>, iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxx, elsie.wahlig@xxxxxxx, amit.shah@xxxxxxxxxxxx |
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Wed, 16 Jan 2008 09:16:38 -0800 |
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<C3B3E529.1AEAC%Keir.Fraser@xxxxxxxxxxxx> |
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On Wed, 2008-01-16 at 16:45 +0000, Keir Fraser wrote:
> On 16/1/08 16:34, "Wei Wang2" <wei.wang2@xxxxxxx> wrote:
>
> > 1) Before submitting io request to generic block layer, block backend
> > driver will invoke GNTTABOPs to map granted remote pages . However
> > creating iommu mapping only in GNTTABOP not very enough because local
> > pages will also be submitted to block layer and they should also be
> > translated by iommu.
>
> Local pages could always be mapped into the iommu, and only remote pages
> would need to be temporarily mapped via the gnttab hooks.
I remembered that vtd patch used to hook page assignment to for this,
but it was soon replaced with statical 1:1 mapping. Could you suggest me
how to trace local page changes instead of mapping whole the physical
ram?
> 2) When dma layer is invoked to prepare a bus address for native block
> > device driver. It would be better to have a "hypervisor-aware" dma layer
> > which always maps virtual address to bus address via hypercall.
> > __gnttab_dma_map_page() might be a good place to trigger this new
> > hypercall. Both remote and local pages can be mapped by this way.
>
> An extra hypercall here will likely hurt performance.
I have implemented a prototype for this which removes 1:1 mapping and invoke a
hypercall for
dma mapping. Since block driver uses dma_map_sg heavily which is easy to batch,
I have not seen dramatic performance loss.
-Wei
> -- Keir
>
>
>
>
-Wei
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