Re: [Qemu-devel] [PATCH 1/2] KVM: page track: add a new notifier type: track_flush_slot

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On 10/19/2016 07:56 PM, Paolo Bonzini wrote:


On 19/10/2016 07:45, Xiao Guangrong wrote:


On 10/19/2016 10:32 AM, Jike Song wrote:
+EXPORT_SYMBOL_GPL(vfio_group_set_usrdata);
+
+void *vfio_group_get_usrdata(struct vfio_group *group)
+{
+    return group->usrdata;
+}
+EXPORT_SYMBOL_GPL(vfio_group_get_usrdata);
+
+void *vfio_group_get_usrdata_by_device(struct device *dev)
+{
+    struct vfio_group *vfio_group;
+
+    vfio_group = __vfio_group_get_from_iommu(dev->iommu_group);

We actually need to use iommu_group_get() here.  Kirti adds a
vfio_group_get_from_dev() in v9 03/12 that does this properly.

+    if (!vfio_group)
+        return NULL;
+
+    return vfio_group_get_usrdata(vfio_group);

I am worrying if the kvm instance got from group->usrdata is safe
enough? What happens if you get the instance after kvm released
kvm-vfio device?

It shouldn't happen if you use kvm_get_kvm and kvm_put_kvm properly.  It
is almost okay in the patch, just:


How about if KVM releases kvm-vfio device between vfio_group_get_usrdata()
and get_kvm()?

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