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    SubjectRe: [PATCH v4 03/12] iommu: Add attach/detach_dev_pasid domain ops
    On Thu, Apr 21, 2022 at 01:21:12PM +0800, Lu Baolu wrote:
    > Attaching an IOMMU domain to a PASID of a device is a generic operation
    > for modern IOMMU drivers which support PASID-granular DMA address
    > translation. Currently visible usage scenarios include (but not limited):
    >
    > - SVA (Shared Virtual Address)
    > - kernel DMA with PASID
    > - hardware-assist mediated device
    >
    > This adds a pair of common domain ops for this purpose and adds helpers
    > to attach/detach a domain to/from a {device, PASID}. Some buses, like
    > PCI, route packets without considering the PASID value. Thus a DMA target
    > address with PASID might be treated as P2P if the address falls into the
    > MMIO BAR of other devices in the group. To make things simple, these
    > interfaces only apply to devices belonging to the singleton groups, and
    > the singleton is immutable in fabric i.e. not affected by hotplug.
    >
    > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
    [...]
    > +/*
    > + * Use standard PCI bus topology, isolation features, and DMA
    > + * alias quirks to check the immutable singleton attribute. If
    > + * the device came from DT, assume it is static and then
    > + * singleton can know from the device count in the group.
    > + */
    > +static bool device_group_immutable_singleton(struct device *dev)
    > +{
    > + struct iommu_group *group = iommu_group_get(dev);
    > + int count;
    > +
    > + if (!group)
    > + return false;
    > +
    > + mutex_lock(&group->mutex);
    > + count = iommu_group_device_count(group);
    > + mutex_unlock(&group->mutex);
    > + iommu_group_put(group);
    > +
    > + if (count != 1)
    > + return false;
    > +
    > + if (dev_is_pci(dev)) {
    > + struct pci_dev *pdev = to_pci_dev(dev);
    > +
    > + /*
    > + * The device could be considered to be fully isolated if
    > + * all devices on the path from the device to the host-PCI
    > + * bridge are protected from peer-to-peer DMA by ACS.
    > + */
    > + if (!pci_acs_path_enabled(pdev, NULL, REQ_ACS_FLAGS))
    > + return false;
    > +
    > + /* Filter out devices which has any alias device. */
    > + if (pci_for_each_dma_alias(pdev, has_pci_alias, pdev))
    > + return false;

    Aren't aliases already added to the group by pci_device_group()? If so
    it's part of the count check above

    > +
    > + return true;
    > + }
    > +
    > + /*
    > + * If the device came from DT, assume it is static and then
    > + * singleton can know from the device count in the group.
    > + */
    > + return is_of_node(dev_fwnode(dev));

    I don't think DT is relevant here because a platform device enumerated
    through ACPI will also have its own group. It should be safe to stick to
    what the IOMMU drivers declare with their device_group() callback. Except
    for PCI those groups should be immutable so we can return true here.

    Thanks,
    Jean

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