On 10/19/2016 10:14 PM, Paolo Bonzini wrote:
On 19/10/2016 15:39, Xiao Guangrong wrote:
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()?
That cannot happen as long as there is a struct file* for the device
(see kvm_ioctl_create_device and kvm_device_release). Since you're
sending a ioctl to it, it's fine.
I understood that KVM side is safe, however, vfio side is independent with
kvm and the user of usrdata can fetch kvm struct at any time, consider
this scenario:
CPU 0 CPU 1
KVM: VFIO/userdata user
kvm_ioctl_create_device
get_kvm()
vfio_group_get_usrdata(vfio_group)
kvm_device_release
put_kvm()
!!! kvm refcount has gone
use KVM struct
Then, the user of userdata have fetched kvm struct but the refcount has already gone.
What i missed?
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