On Thu, 17 Nov 2016 13:24:59 +0800
Jike Song <jike.song@xxxxxxxxx> wrote:
> On 11/17/2016 03:45 AM, Alex Williamson wrote:
> > Perhaps calling it a filter is not correct, I was thinking that a
> > vendor driver would register the notifier with a set of required
> > events. The driver would need to handle/ignore additional events
> > outside of the required mask. There are certainly some complications
> > to this model though that I hadn't thought all the way through until
> > now. For instance what if we add event XYZ in the future and the
> > vendor driver adds this to their required mask. If we run that on an
> > older kernel where the vfio infrastructure doesn't know about that
> > event, the vendor driver needs to fail, or at least know that event is
> > not supported and retry with a set of supported events.
> >
> > There's another problem with my proposal too, we can't put a single
> > notifier_block on multiple notifier_block heads, that just doesn't
> > work. So we probably need to separate a group notifier from an iommu
> > notifier, the vendor driver will need to register for each.
> >
> > Maybe we end up with something like:
> >
> > int vfio_register_notifier(struct device *dev,
> > vfio_notify_type_t type,
> > unsigned long *required_events,
> > struct notifier_block *nb);
> >
> > typedef unsigned short vfio_notify_type_t;
> > enum vfio_notify_type {
> > VFIO_IOMMU_NOTIFY = (__force vfio_notify_type_t)0,
> > VFIO_GROUP_NOTIFY = (__force vfio_notify_type_t)1,
> > };
> >
> > (stealing this from pci_dev_flags_t, hope it works)
> >
> > A VFIO_GROUP_NOTIFY would add the notifier_block to the vfio_group, a
> > VFIO_IOMMU_NOTIFY would add it to vfio_iommu. Each would have their
> > own unique set of events and each would compare their supported events
> > to the required events by the caller. Supported events would be
> > cleared from the callers required_events arg. If required_events still
> > has bits set, the notifier_block is not registered, an error is
> > returned, and the caller can identify the unsupported events by the
> > remaining bits in the required_events arg. Can that work? Thanks,
>
> Let me summarize the discussion:
>
> - There should be 2 notifier heads, one in vfio_iommu another in vfio_group;
> - vfio_{un}register_notifier() has the type specified in parameter
> - In vfio_register_notifier, maybe:
>
> static vfio_iommu_register_notifier() {..}
> static vfio_group_register_notifier() {..}
> int vfio_register_notififer(type..
> {
> if (type == VFIO_IOMMU_NOTIFY)
> return vfio_iommu_register_notifier();
> if (type == VFIO_GROUP_NOTIFY)
> return vfio_group_register_notifier();
> }
>
>
>
> What's more, if we still want registration to be done in mdev framework,
> we should change parent_ops:
>
> - rename 'notifier' to 'iommu_notifier'
> - add "group_notifier"
> - Add a group_events and a iommu_events to indicate what events vendor is
> interested in, respectively
>
> or otherwise don't touch it from mdev framework at all?
I think we should remove the notifier from the mdev framework and have
the vendor drivers call vfio_{un}register_notifier() directly. Note:
- vfio_group_release() should be modified to remove any notifier
blocks remaining to prevent a stale call chain for the next user.
- vfio_sanity_check_pfn_list() should be modified to WARN_ON remaining
notifier blocks on the vfio_iommu (ie. vendor drivers will need to
actively remove iommu notifiers since the vfio_iommu can persist
beyond the attachment of the mdev group, the WARN_ON will promote a
proactive approach to surfacing such issues).
I'd like to get Kirti's current series in linux-next ASAP, so please
submit a follow-on series to make these changes. I hope we can get
that finalized and added on top of Kirti's series before the v4.10
merge window opens. Thanks,
Alex
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