Morning Jason, On Fri, 14 May 2021 10:39:39 -0300, Jason Gunthorpe wrote:
> On Fri, May 14, 2021 at 01:17:23PM +0000, Tian, Kevin wrote: > > > From: Jason Gunthorpe <j...@ziepe.ca> > > > 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. > > Eh? That sounds messed up. > > The IOASID is the page table. If you have one IOASID and you attach it > to 4 IOMMU routings (be it pasid, rid, whatever) then there should > only ever by one page table. yes, ioasid is the page table. But if want to let the 4 mdevs share the same page table, it would be natural to let them share a domain. Since mdev_device is not hw device, we should not let it participate in the IOMMU. Therefore we got the aux-domain concept. mdev(RID#+PASID) is attached to aux-domain. Such solution also fits the hybrid cases. e.g. When there are both PF(RID#1) and mdev(RID#2+PASID) assigned to an ioasid, they should share a page table as well. right? Surely we cannot attach the PF(RID#1) to the domain of mdev's parent device(RID#2). Good way is PF(RID#1) and the mdev (RID#2+PASID) attached to a single domain. This domain is the primary domain for the PF(RID#1) but an aux-domain mdev's paretn(RID#2). -- Regards, Yi Liu _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
