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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-04-04 at 11:25 +0100, Julien Grall wrote:
> On 04/04/2014 10:40 AM, Ian Campbell wrote:
> 
> > We really need to be able to manage this transition in a compatible way,
> > that means new kernels working on old hypervisors as well as old kernels
> > working on new hypervisors (it's obviously fine for this case to bounce
> > when it doesn't need to).
> 
> It's not possible because a same platform can have both protected and
> non-protected devices. The Linux has to know in some way if the DMA has
> to be program with IPA or PA.

Then there must be a negotiation between Xen and the Linux kernel so Xen
can know which case to apply.

e.g. if the kernel does not advertise support for protected devices then
Xen must act as if no IOMMU was present. 

> The only way is to disable the IOMMU, or don't use partition disk for
> guest, until the DOM0 will be able to disable swiotlb.
> 



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