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Re: [Xen-devel] [PATCH v3 12/13] xen/arm: Add the property "protected-devices" in the hypervisor node

Hi Ian,

Sorry, I forgot to answer to this email...

On 19/03/14 10:33, Ian Campbell wrote:
On Tue, 2014-03-18 at 20:09 +0000, Julien Grall wrote:
Hi Ian,

On 03/18/2014 04:48 PM, Ian Campbell wrote:
On Tue, 2014-03-11 at 15:49 +0000, Julien Grall wrote:
DOM0 is using the swiotlb to bounce DMA. With the IOMMU support in Xen,
protected devices should not use it.

Only Xen is abled to know if an IOMMU protects the device. The new property
"protected-devices" is a list of device phandles protected by an IOMMU.

Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>

     This patch *MUST NOT* be applied until we agreed on a device binding
     the device tree folks. DOM0 can run safely with swiotlb on protected
     devices while LVM is not used for guest disk.

LVM works these days I think.

With this patch series applied, LVM will be broken if the hard drive is
protected by an IOMMU.


If the guest is using LVM for its block, bouncing via the swiotlb with IOMMU enabled will result to wrong mapping. If I remember correctly it's because SWIOTLB DMA address is a physical address and not an IPA. So the IOMMU will rejected the request.

So we have to by-pass swiotlb in this case.

It's the case on midway, the platform will crash just after the guest
begins to boot.

This configuration works today (osstest tests it) so this would be a
regression. Can you sort this please?

As said above with IOMMU enabled I won't be able to sort it until my patch series for Linux will be upstreamed.


Julien Grall

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