On Thu, Feb 09, 2023 at 01:13:07PM -0800, Nicolin Chen wrote: > On Thu, Feb 09, 2023 at 04:00:52AM +0000, Tian, Kevin wrote: > > > > From: Nicolin Chen <nicolinc@xxxxxxxxxx> > > > Sent: Wednesday, February 8, 2023 5:18 AM > > > > > > iommu_group_replace_domain() is introduced to support use cases where > > > an > > > iommu_group can be attached to a new domain without getting detached > > > from > > > the old one. This replacement feature will be useful, for cases such as: > > > 1) vPASID mode, when a guest wants to replace a single pasid (PASID=0) > > > table with a larger table (PASID=N) > > > 2) Nesting mode, when switching the attaching device from an S2 domain > > > to an S1 domain, or when switching between relevant S1 domains. > > > as it allows these cases to switch seamlessly without a DMA disruption. > > > > > > So, call iommu_group_replace_domain() in the iommufd_device_do_attach(). > > > And add a __iommmufd_device_detach helper to allow the replace routine > > > to > > > do a partial detach on the current hwpt that's being replaced. Though the > > > updated locking logic is overcomplicated, it will be eased, once those > > > iopt_table_add/remove_ioas and list_add/del calls are moved to hwpt's > > > allocation/destroy() functions in the coming nesting series, as that'll > > > depend on a new ->domain_alloc_user op in the iommu core. > > > > then why not moving those changes into this series to make it simple? > > The simplification depends on the new ->domain_alloc_user op and > its implementation in SMMU driver, which would be introduced by > the nesting series of VT-d and SMMU respectively. Since we are not fixing all the drivers at this point, this argument doesn't hold water. It is as I said in the other email, there should be no changes to the normal attach/replace path when adding manual HWPT creation - once those are removed there should be minimal connection between these two series. Jason
