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    SubjectRe: [PATCH v2 08/10] iommufd/device: Use iommu_group_replace_domain()
    On Mon, Feb 13, 2023 at 10:49:34AM -0400, Jason Gunthorpe wrote:
    > On Sun, Feb 12, 2023 at 11:48:30PM -0800, Nicolin Chen wrote:
    >
    > > What about point 1? If dev2 and dev3 are already replaced when
    > > doing iommu_group_replace_domain() on dev1, their idev objects
    > > still have the old hwpt/iopt until user space does another two
    > > IOCTLs on them, right?
    >
    > We have a complicated model for multi-device groups...
    >
    > The first device in the group to change domains must move all the
    > devices in the group
    >
    > But userspace is still expected to run through and change all the
    > other devices
    >
    > So replace should be a NOP if the group is already linked to the right
    > domain.
    >
    > This patch needs to make sure that incosistency in the view betwen the
    > iommu_group and the iommufd model doesn't cause a functional
    > problem.

    Yea, I was thinking that we'd need to block any access to the
    idev->hwpt of a pending device's, before the kernel finishes
    the "NOP" IOCTL from userspace, maybe with a helper:
    (iommu_get_domain_for_dev(idev->dev) != idev->hwpt->domain)

    Thanks
    Nic

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