Re: [RFC PATCH 03/10] iommu/vt-d: Allocate groups for mediated devices

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 24 Jul 2018 12:30:35 +0100
Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:

> Hi Baolu,
> 
> On 24/07/18 03:22, Lu Baolu wrote:
> > Hi,
> > 
> > On 07/23/2018 12:44 PM, Liu, Yi L wrote:  
> >>> From: Lu Baolu [mailto:baolu.lu@linux.intel.com]
> >>> Sent: Sunday, July 22, 2018 2:09 PM
> >>>
> >>> With the Intel IOMMU supporting PASID granularity isolation and protection, a
> >>> mediated device could be isolated and protected by an IOMMU unit. We need to
> >>> allocate a new group instead of a PCI group.  
> >> Existing vfio mdev framework also allocates an iommu group for mediate device.
> >>
> >> mdev_probe()
> >>   |_ mdev_attach_iommu()
> >>        |_ iommu_group_alloc()  
> > 
> > When external components ask iommu to allocate a group for a device,
> > it will call pci_device_group in Intel IOMMU driver's @device_group
> > callback. In another word, current Intel IOMMU driver doesn't aware
> > the mediated device and treat all devices as PCI ones. This patch
> > extends the @device_group call back to make it aware of a mediated
> > device.  
> 
> I agree that allocating two groups for an mdev seems strange, and in my
> opinion we shouldn't export the notion of mdev to IOMMU drivers.

Yep, I was just thinking the same thing.  This is too highly integrated
into VT-d and too narrowly focused on PASID being the only way that an
mdev could make use of the IOMMU.  Thanks,

Alex