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    SubjectRe: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs
    Hi Jason,

    On Tue, 30 Mar 2021 10:43:13 -0300, Jason Gunthorpe <jgg@nvidia.com> wrote:

    > > If two mdevs from the same PF dev are assigned to two VMs, the PASID
    > > table will be shared. IOASID set ensures one VM cannot program another
    > > VM's PASIDs. I assume 'secure context' is per VM when it comes to host
    > > PASID.
    >
    > No, the mdev device driver must enforce this directly. It is the one
    > that programms the physical shared HW, it is the one that needs a list
    > of PASID's it is allowed to program *for each mdev*
    >
    This requires the mdev driver to obtain a list of allowed PASIDs(possibly
    during PASID bind time) prior to do enforcement. IMHO, the PASID enforcement
    points are:
    1. During WQ configuration (e.g.program MSI)
    2. During work submission

    For VT-d shared workqueue, there is no way to enforce #2 in mdev driver in
    that the PASID is obtained from PASID MSR from the CPU and submitted w/o
    driver involvement. The enforcement for #2 is in the KVM PASID translation
    table, which is per VM.

    For our current VFIO mdev model, bind guest page table does not involve
    mdev driver. So this is a gap we must fill, i.e. include a callback from
    mdev driver?

    > ioasid_set doesn't seem to help at all, certainly not as a concept
    > tied to /dev/ioasid.
    >
    Yes, we can take the security role off ioasid_set once we have per mdev
    list. However, ioasid_set being a per VM/mm entity also bridge
    communications among kernel subsystems that don't have direct call path.
    e.g. KVM, VDCM and IOMMU.

    > > No. the mdev driver consults with IOASID core When the guest programs a
    > > guest PASID on to he mdev. VDCM driver does a lookup:
    > > host_pasid = ioasid_find_by_spid(ioasid_set, guest_pasid);
    >
    > This is the wrong layering. Tell the mdev device directly what it is
    > allowed to do. Do not pollute the ioasid core with security stuff.
    >
    > > > I'd say you shoul have a single /dev/ioasid per VM and KVM should
    > > > attach to that - it should get all the global events/etc that are not
    > > > device specific.
    > > >
    > > You mean a single /dev/ioasid FD per VM and KVM? I think that is what we
    > > are doing in this set. A VM process can only open /dev/ioasid once, then
    > > use the FD for allocation and pass the PASID for bind page table etc.
    >
    > Yes, I think that is reasonable.
    >
    > Tag all the IOCTL's with the IOASID number.
    >
    > > > Not sure what guest-host PASID means, these have to be 1:1 for device
    > > > assignment to work - why would use something else for mdev?
    > > >
    > > We have G-H PASID translation. They don't have to be 1:1.
    > > IOASID Set Private ID (SPID) is intended as a generic solution for
    > > guest PASID. Could you review the secion Section: IOASID Set Private ID
    > > (SPID) in the doc patch?
    >
    > Again this only works for MDEV? How would you do translation for a
    > real PF/VF?
    >
    Right, we will need some mediation for PF/VF.

    > So when you 'allow' a mdev to access a PASID you want to say:
    > Allow Guest PASID A, map it to host PASID B on this /dev/ioasid FD
    >
    > ?
    >
    Host and guest PASID value, as well as device info are available through
    iommu_uapi_sva_bind_gpasid(), we just need to feed that info to mdev driver.

    > That seems like a good helper library to provide for drivers to use,
    > but it should be a construct entirely contained in the driver.
    why? would it be cleaner if it is in the common code?

    Thanks,

    Jacob

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