commit c3635da2 upstream.

Before the guest finishes the device initialization, the device can be
removed anytime by the host, and after that the host won't respond to
the guest's request, so the guest should be prepared to handle this
case.

Add a polling mechanism to detect device presence.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
[lorenzo.pieralisi@arm.com: edited commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>