passthrough: simplify locking and logging

passthrough: simplify locking and logging

Dropping the pcidevs lock between calling device_assigned() and
assign_device() means that the latter has to do the same check as the
former for no obvious gain. Also, since long running operations under
pcidevs lock already drop the lock and return -ERESTART periodically there
is little point in immediately failing an assignment operation with
-ERESTART just because the pcidevs lock could not be acquired (for the
second time, having already blocked on acquiring the lock in
device_assigned()).

This patch instead acquires the lock once for assignment (or test assign)
operations directly in iommu_do_pci_domctl() and thus can remove the
duplicate domain ownership check in assign_device(). Whilst in the
neighbourhood, the patch also removes some debug logging from
assign_device() and deassign_device() and replaces it with proper error
logging, which allows error logging in iommu_do_pci_domctl() to be
removed.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>