RE: [PATCH] vfio: fix deadlock between group lock and kvm lock

[Tian, Kevin]

> From: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
> Sent: Wednesday, February 1, 2023 4:07 AM
> 
> -	device->kvm = kvm;
> +	/*
> +	 * Get the KVM pointer currently associated with the group, if there
> +	 * is one, and obtain a reference now that will be held until the
> +	 * open_count reaches 0.  Save the pointer in the device for use by
> +	 * drivers.
> +	 */
> +	spin_lock_irqsave(&group->kvm_ref_lock, flags);
> +	if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm))
> +		device->kvm = group->kvm;
> +	spin_unlock_irqrestore(&group->kvm_ref_lock, flags);
> +

No group reference in vfio_main.c. 

btw Yi, looks the deadlock issue also exists in your cdev work.

kvm_vfio_release() holds kvm lock and then try to acquire
device->device_set->lock in vfio_device_file_set_kvm().

vfio_device_ioctl_bind_iommufd() holds device->device_set->lock
and then call vfio_device_open() which finally hit kvm lock
acquisition in driver's open_device routine (e.g. vfio-ap).

A similar fix is required in your series.

Thanks
Kevin