Re: [PATCH v5 16/21] KVM: vfio: add s390x hook to register KVM guest designation

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 4/8/22 8:45 AM, Jason Gunthorpe wrote:
> On Mon, Apr 04, 2022 at 01:43:44PM -0400, Matthew Rosato wrote:
>> At the time a KVM is associated with a vfio group, s390x zPCI devices
>> must register a special guest indication (GISA designation) to allow
>> for the use of interpretive execution facilities.  This indication is
>> used to ensure that only the specified KVM can interact with the device.
>> Similarly, the indication must be removed once the KVM is no longer
>> associated with the device.
>>
>> This patch adds an s390-specific hook to invoke a KVM registration routine
>> for each device associated with the iommu group; in reality, it will be a
>> NOP for all but zPCI devices on s390x.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>> ---
>>   virt/kvm/vfio.c | 35 ++++++++++++++++++++++++++++++++++-
>>   1 file changed, 34 insertions(+), 1 deletion(-)
> 
> I wonder if this should be done in the vfio_pci side from the existing
> kvm notifier
> 

So you mean rather than hooking into virt as I do here, drive something 
out of drivers/vfio/vfio.c:vfio_group_set_kvm?  Note, the kvm notifier 
is handled in vfio, not vfio_pci, so if you want to handle it in 
vfio_pci I think we'd need to add a new routine to vfio_device_ops and 
only define it vfio_pci for s390

e.g.

static const struct vfio_device_ops vfio_pci_ops = {
	.name		= "vfio-pci",
[...]
#ifdef CONFIG_S390
	.set_kvm = vfio_pci_zdev_set_kvm,
#endif
};

and something like...

void vfio_group_set_kvm(struct vfio_group *group, struct kvm *kvm)
{
	struct vfio_device *vdev;
	group->kvm = kvm;

	mutex_lock(&group->device_lock);
	list_for_each_entry(vdev, &group->device_list, group_next) {
		if (vdev->ops->set_kvm)
			it->ops->set_kvm(vdev, kvm);
	}
	mutex_unlock(&group->device_lock);

	blocking_notifier_call_chain(&group->notifier,
				VFIO_GROUP_NOTIFY_SET_KVM, kvm);
}