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    SubjectRE: [PATCH RFC v2 02/11] iommu: Add iommu_group_singleton_lockdown()
    Date
    > From: Lu Baolu <baolu.lu@linux.intel.com>
    > Sent: Wednesday, March 30, 2022 1:00 PM
    > >
    > > btw I'm not sure whether this is what SVA requires. IIRC the problem with
    > > SVA is because PASID TLP prefix is not counted in PCI packet routing 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. This is why the
    > > original code needs to strictly apply SVA in a group containing a single
    > > device, instead of a group attached by a single driver, unless we want to
    > > reserve those MMIO ranges in CPU VA space.
    >
    > You are right. But I don't think the IOMMU core is able to guarantee
    > above in a platform/device-agnostic way. Or any suggestions?
    >
    > I guess this should be somewhat off-loaded to the device driver which
    > knows details of the device. The device driver should know this and
    > guarantee it before calling
    > iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA).

    How would the device driver know whether SVA requests from a
    device might be mis-interpreted as p2p by upstreaming ports?

    >
    > This patch itself just replaces the existing
    > "iommu_group_device_count(group) != 1" logic with a new one based on the
    > group ownership logistics. The former is obviously not friendly to
    > device hot joined afterward.
    >

    IMHO this replacement changes the semantics and device hotplug is
    something that we must deal with...

    Thanks
    Kevin
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