Messages in this thread | | | From | "Tian, Kevin" <> | Subject | RE: [PATCH v2 1/3] iommufd: Add devices_users to track the hw_pagetable usage by device | Date | Sun, 29 Jan 2023 09:23:05 +0000 |
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> From: Nicolin Chen <nicolinc@nvidia.com> > Sent: Sunday, January 29, 2023 5:18 AM > > 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. > > Add a devices_users in struct iommufd_hw_pagetable to track the users of
device_users
> hw_pagetable by the attached devices. Make this field as a pointer, only > allocate for a stage-2 hw_pagetable. A stage-1 hw_pagetable should reuse > the stage-2 hw_pagetable's devices_users, because when a device attaches > to a stage-1 hw_pagetable, linking the stage-2 hwpt to the IOAS is still > required. So, with a nested configuration, increase the devices_users on > the stage-2 (parent) hwpt, no matter a device is attached to the stage-1 > or the stage-2 hwpt.
Above is very confusing w/o seeing the full series of nesting support.
As a preparatory step this should focus on existing code and what this series tries to achieve. e.g. I'd not make device_users a pointer here. Do that incrementally when the nesting support comes.
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