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    SubjectRe: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs
    On Wed, May 26, 2021 at 02:48:03AM +0530, Kirti Wankhede wrote:
    >
    >
    > On 5/26/2021 1:22 AM, Jason Gunthorpe wrote:
    > > On Wed, May 26, 2021 at 12:56:30AM +0530, Kirti Wankhede wrote:
    > >
    > > > 2. iommu backed mdev devices for SRIOV where mdev device is created per
    > > > VF (mdev device == VF device) then that mdev device has same iommu
    > > > protection scope as VF associated to it.
    > >
    > > This doesn't require, and certainly shouldn't create, a fake group.
    > >
    > > Only the VF's real IOMMU group should be used to model an iommu domain
    > > linked to a VF. Injecting fake groups that are proxies for real groups
    > > only opens the possibility of security problems like David is
    > > concerned with.
    > >
    >
    > I think this security issue should be addressed by letting mdev device
    > inherit its parent's iommu_group, i.e. VF's iommu_group here.

    No, that doesn't work. AIUI part of the whole point of mdevs is to
    allow chunks of a single PCI function to be handed out to different
    places, because they're isolated from each other not by the system
    IOMMU, but by a combination of MMU hardware in the hardware (e.g. in a
    GPU card) and software in the mdev driver. If mdevs inherited the
    group of their parent device they wouldn't count as isolated from each
    other, which they should.

    >
    > Kirti
    >
    > > Max's series approaches this properly by fully linking the struct
    > > pci_device of the VF throughout the entire VFIO scheme, including the
    > > group and container, while still allowing override of various VFIO
    > > operations.
    > >
    > > Jason
    > >
    >

    --
    David Gibson | I'll have my music baroque, and my code
    david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
    | _way_ _around_!
    http://www.ozlabs.org/~dgibson
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