Messages in this thread | | | Date | Mon, 30 Jan 2023 11:02:25 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device |
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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.
Jason
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