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    SubjectRE: [PATCH v2 3/3] iommufd/device: Change iommufd_hw_pagetable_has_group to device centric
    Date
    > From: Nicolin Chen <nicolinc@nvidia.com>
    > Sent: Monday, January 30, 2023 6:22 PM
    >
    > On Sun, Jan 29, 2023 at 02:38:55AM -0800, Nicolin Chen wrote:
    >
    > > > > @@ -385,10 +372,8 @@ void iommufd_device_detach(struct
    > > > > iommufd_device *idev)
    > > > > struct iommufd_hw_pagetable *hwpt = idev->hwpt;
    > > > >
    > > > > mutex_lock(&hwpt->ioas->mutex);
    > > > > - mutex_lock(&hwpt->devices_lock);
    > > > > refcount_dec(hwpt->devices_users);
    > > > > - list_del(&idev->devices_item);
    > > > > - if (!iommufd_hw_pagetable_has_group(hwpt, idev->group)) {
    > > > > + if (iommufd_hw_pagetable_has_device(hwpt, idev->dev)) {
    > > > > if (refcount_read(hwpt->devices_users) == 1) {
    > > > > iopt_table_remove_domain(&hwpt->ioas->iopt,
    > > > > hwpt->domain);
    > > > > @@ -397,7 +382,6 @@ void iommufd_device_detach(struct
    > iommufd_device
    > > > > *idev)
    > > > > iommu_detach_group(hwpt->domain, idev->group);
    > > > > }
    > > >
    > > > emmm how do we track last device detach in a group? Here the first
    > > > device detach already leads to group detach...
    > >
    > > Oh no. That's a bug. Thanks for catching it.
    > >
    > > We need an additional refcount somewhere to track the number of
    > > attached devices in the iommu_group.
    >
    > Wondering if we can let iommu_attach/detach_device handle this:
    >

    that is the desired way to fully remove group awareness in iommufd.

    but iirc there were some concerns on changing their semantics. But
    I don't remember the detail now. Jason might know. also +Baolu/Robin.

    otherwise as long as the group attach/detach continues to be used
    then identifying last device in the group always needs some hack
    within iommufd itself.

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