Re: [PATCH v2 1/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

[Matthew Rosato]

On 5/19/22 12:23 PM, Tony Krowiak wrote:
> I made a few comments, but other than that this looks good to
> me:
>
> Reviewed-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>

...

> I'm not sure what version of the code on which the patch was rebased, 

Was on top of Jason's vfio_group_locking series, but now would apply on 
vfio-next since Alex pulled that series in to vfio-next.

> but in the
> latest master branch from our repository the kvm_get_kvm(kvm) function is
> called inside of the if block below. I'm fine with moving outside of the 
> block, but
> I don't see a corresponding removal of it from inside the block.

Yeah, I didn't notice those there.  v3 will simply remove my get/put 
additions and leave yours as-is.

...

> > vfio_ap_mdev_group_notifier;
> > -    events = VFIO_GROUP_NOTIFY_SET_KVM;
> > +    if (!vdev->kvm)
> > +        return -EPERM;
>
> Perhaps -EINVAL or -EFAULT?

Whichever you'd prefer?  If I don't hear back I'll just use -EINVAL in v3.

> > -    ret = vfio_register_notifier(vdev, VFIO_GROUP_NOTIFY, &events,
> > -                     &matrix_mdev->group_notifier);
> > +    ret = vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
> >       if (ret)
> >           return ret;
> > @@ -1415,12 +1400,11 @@ static int vfio_ap_mdev_open_device(struct 
> > vfio_device *vdev)
> >       ret = vfio_register_notifier(vdev, VFIO_IOMMU_NOTIFY, &events,
> >                        &matrix_mdev->iommu_notifier);
> >       if (ret)
> > -        goto out_unregister_group;
> > +        goto err_kvm;
> >       return 0;
> > -out_unregister_group:
> > -    vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> > -                 &matrix_mdev->group_notifier);
> > +err_kvm:
> > +    vfio_ap_mdev_unset_kvm(matrix_mdev);
> >       return ret;
> >   }
> > @@ -1431,8 +1415,6 @@ static void vfio_ap_mdev_close_device(struct 
> > vfio_device *vdev)
> >       vfio_unregister_notifier(vdev, VFIO_IOMMU_NOTIFY,
> >                    &matrix_mdev->iommu_notifier);
> > -    vfio_unregister_notifier(vdev, VFIO_GROUP_NOTIFY,
> > -                 &matrix_mdev->group_notifier);
> >       vfio_ap_mdev_unset_kvm(matrix_mdev);
>
> I'm not sure if this matters, but the vfio_ap_mdev_unset_kvm(matrix_mdev)
> function uses the KVM pointer stored in matrix_mdev->kvm. I can't imagine
> the KVM pointer stored in vdev->kvm being different than matrix_mdev->kvm,

With this patch matrix_mdev->kvm is set from the value in vdev->kvm 
during vfio_ap_mdev_set_kvm (basically, doing the work that the notifier 
was doing but instead of getting it from notifier data get it from the 
vfio_device)

> but thought I should point it out. Previously, this function was called 
> by the
> notifier handler which did not have access to the KVM pointer which is 
> why it
> was retrieved from matrix_mdev->kvm. Even if the vdev->kvm and
> matrix_mdev->kvm did not match, we should probably go ahead and call
> the unset function anyway to remove access to AP resources for the guest 
> and
> reset the queues.