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

[Julien Grall <julien.grall@xxxxxxxxxx>]

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.
> How/why?
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.
Regards,

--
Julien Grall

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