On Tue, Aug 23, 2011 at 01:33:14PM -0400, Aaron Fabbri wrote: > On 8/23/11 10:01 AM, "Alex Williamson" <alex.williamson@xxxxxxxxxx> wrote: > > The iommu domain would probably be allocated when the first device is > > bound to vfio. As each device is bound, it gets attached to the group. > > DMAs are done via an ioctl on the group. > > > > I think group + uiommu leads to effectively reliving most of the > > problems with the current code. The only benefit is the group > > assignment to enforce hardware restrictions. We still have the problem > > that uiommu open() = iommu_domain_alloc(), whose properties are > > meaningless without attached devices (groups). Which I think leads to > > the same awkward model of attaching groups to define the domain, then we > > end up doing mappings via the group to enforce ordering. > > Is there a better way to allow groups to share an IOMMU domain? > > Maybe, instead of having an ioctl to allow a group A to inherit the same > iommu domain as group B, we could have an ioctl to fully merge two groups > (could be what Ben was thinking): > > A.ioctl(MERGE_TO_GROUP, B) > > The group A now goes away and its devices join group B. If A ever had an > iommu domain assigned (and buffers mapped?) we fail. > > Groups cannot get smaller (they are defined as minimum granularity of an > IOMMU, initially). They can get bigger if you want to share IOMMU > resources, though. > > Any downsides to this approach? As long as this is a 2-way road its fine. There must be a way to split the groups again after the guest exits. But then we are again at the super-groups (aka meta-groups, aka uiommu) point. Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
