> From: Jason Gunthorpe <jgg@xxxxxxxx> > Sent: Thursday, May 13, 2021 8:01 PM > > On Thu, May 13, 2021 at 03:28:52AM +0000, Tian, Kevin wrote: > > > Are you specially concerned about this iommu_device hack which > > directly connects mdev_device to iommu layer or the entire removed > > logic including the aux domain concept? For the former we are now > > following up the referred thread to find a clean way. But for the latter > > we feel it's still necessary regardless of how iommu interface is redesigned > > to support device connection from the upper level driver. The reason is > > that with mdev or subdevice one physical device could be attached to > > multiple domains now. there could be a primary domain with DOMAIN_ > > DMA type for DMA_API use by parent driver itself, and multiple auxiliary > > domains with DOMAIN_UNMANAGED types for subdevices assigned to > > different VMs. > > Why do we need more domains than just the physical domain for the > parent? How does auxdomain appear in /dev/ioasid? > Another simple reason. Say you have 4 mdevs each from a different parent are attached to an ioasid. If only using physical domain of the parent + PASID it means there are 4 domains (thus 4 page tables) under this IOASID thus every dma map operation must be replicated in all 4 domains which is really unnecessary. Having the domain created with ioasid and allow a device attaching to multiple domains is much cleaner for the upper-layer drivers to work with iommu interface. Thanks Kevin
