Hi Yi,
On 1/17/23 14:49, Yi Liu wrote:
> This is to avoid a circular refcount problem between the kvm struct and
> the device file. KVM modules holds device/group file reference when the
> device/group is added and releases it per removal or the last kvm reference
> is released. This reference model is ok for the group since there is no
> kvm reference in the group paths.
>
> But it is a problem for device file since the vfio devices may get kvm
> reference in the device open path and put it in the device file release.
> e.g. Intel kvmgt. This would result in a circular issue since the kvm
> side won't put the device file reference if kvm reference is not 0, while
> the vfio device side needs to put kvm reference in the release callback.
>
> To solve this problem for device file, let vfio provide release() which
> would be called once kvm file is closed, it won't depend on the last kvm
> reference. Hence avoid circular refcount problem.
>
> Suggested-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
> virt/kvm/vfio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 0f54b9d308d7..525efe37ab6d 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -364,7 +364,7 @@ static int kvm_vfio_create(struct kvm_device *dev, u32 type);
> static struct kvm_device_ops kvm_vfio_ops = {
> .name = "kvm-vfio",
> .create = kvm_vfio_create,
> - .destroy = kvm_vfio_destroy,
Is it safe to simply remove the destroy cb as it is called from
kvm_destroy_vm/kvm_destroy_devices?
Thanks
Eric
> + .release = kvm_vfio_destroy,
> .set_attr = kvm_vfio_set_attr,
> .has_attr = kvm_vfio_has_attr,
> };
