Re: [Xen-devel] [PATCH for 4.6 13/13] xen/iommu: smmu: Add Xen specific code to be able to use the driver

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 19/02/2015 02:55, Manish wrote:
> On 18/02/15 11:52 pm, Julien Grall wrote:
> > On 18/02/2015 17:30, Jaggi, Manish wrote:
> > > [manish] There are general comments on the data structures
> > > (a) I don't see a use case where for same domain (VM) there would be
> > > different context banks , so linked list may not be required.
> > I guess you mean the list in arm_smmu_xen_domain? All the devices
> > pass-through to a domain may not be protected by the same SMMU.
> > Therefore the context banks are different.
> you are right. For each smmu the context bank instance for a xen domain
> is duplicated with just a change in context bank id. I was thinking can
> it be minimized.
> > Also, for now a context is allocated per-device. It should be rework
> > to share the context between multiple device protected by the same
> > SMMU and pass-through to the same domain.
> Yes, this is exactly I an doing at my end.
> > > (b) Also iommu group may not be relevant for the same reason.
> > > I am curious to find the use cases.
> > The iommu_group is used to store the configuration of the device
> > protected by an SMMU (i.e the stream ids associated to this domain).
> >
> > I'm a bit surprised that you think they are not useful...
> How do we create an iommu_group in xen ? AFAIK an iommu group is a vfio
> group in linux which is assigned to a a VM.
> lkvm run -m 512 -k home/Image ...  --vfio-groups=48, 51
 > For Xen There are 2 ways of attaching devices using xl pci-attach or in
> domU cfg file. Should they create different iommu_groups ?
Why are you talking about VFIO? The iommu_group is created by the SMMU 
when a new device is added (see arm_smmu_device). At the time we are 
speaking, Linux and Xen use one iommu group per-device. No matters what 
VFIO does.
Even though we have two ways to attach PCI on the toolstack, both are 
using the same hypercall at the end.
Regards,

--
Julien Grall

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