Messages in this thread | | | Date | Mon, 30 Jan 2023 12:04:33 -0800 | From | Nicolin Chen <> | Subject | Re: [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device |
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On Mon, Jan 30, 2023 at 03:50:07PM -0400, Jason Gunthorpe wrote: > On Mon, Jan 30, 2023 at 11:27:37AM -0800, Nicolin Chen wrote: > > On Mon, Jan 30, 2023 at 11:02:25AM -0400, Jason Gunthorpe wrote: > > > On Sat, Jan 28, 2023 at 01:18:09PM -0800, Nicolin Chen wrote: > > > > From: Yi Liu <yi.l.liu@intel.com> > > > > > > > > Currently, hw_pagetable tracks the attached devices using a device list. > > > > When attaching the first device to the kernel-managed hw_pagetable, it > > > > should be linked to IOAS. When detaching the last device from this hwpt, > > > > the link with IOAS should be removed too. And this first-or-last device > > > > check is done with list_empty(hwpt->devices). > > > > > > > > However, with a nested configuration, when a device is attached to the > > > > user-managed stage-1 hw_pagetable, it will be added to this user-managed > > > > hwpt's device list instead of the kernel-managed stage-2 hwpt's one. And > > > > this breaks the logic for a kernel-managed hw_pagetable link/disconnect > > > > to/from IOAS/IOPT. e.g. the stage-2 hw_pagetable would be linked to IOAS > > > > multiple times if multiple device is attached, but it will become empty > > > > as soon as one device detached. > > > > > > Why this seems really weird to say. > > > > > > The stage 2 is linked explicitly to the IOAS that drives it's > > > map/unmap > > > > > > Why is there any implicit activity here? There should be no implicit > > > attach of the S2 to an IOAS ever. > > > > I think this is supposed to say the following use case: > > > > Two stage-1 hwpts share the same parent s2_hwpt: > > > > attach device1 to stage-1 hwpt1: > > ... > > if (list_empty(s1_hwpt1->devices)) // empty; true > > iopt_table_add_domain(s2_hwpt->domain); // do once > > s1_hwpt1 device list cnt++; > > ... > > No, this doesn't make sense. > > The s2_hwpt should be created explicitly, not using autodomains
iopt_table_add_domain() is called in iommufd_device_do_attach(), so it's shared by both a created hwpt or autodomain.
> When it is created it should be linked to a single IOAS and that is > when iopt_table_add_domain() should have been called.
I recall we've discussed this that SMMU sets up domain when it attaches the device to, so we made a compromise here...
> The S1 attach should do *nothing* to a S2.
With that compromise, a nested attach flow may be 1) create an s2 hwpt 2) create an s1 hwpt 3) attach dev to s1 calls iopt_table_add_domain()
Thanks Nicolin
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