VT-d: avoid NULL deref on domain_context_mapping_one() error paths

VT-d: avoid NULL deref on domain_context_mapping_one() error paths

First there's a printk() which actually wrongly uses pdev in the first
place: We want to log the coordinates of the (perhaps fake) device
acted upon, which may not be pdev.

Then it was quite pointless for eb19326a328d ("VT-d: prepare for per-
device quarantine page tables (part I)") to add a domid_t parameter to
domain_context_unmap_one(): It's only used to pass back here via
me_wifi_quirk() -> map_me_phantom_function(). Drop the parameter again.

Finally there's the invocation of domain_context_mapping_one(), which
needs to be passed the correct domain ID. Avoid taking that path when
pdev is NULL and the quarantine state is what would need restoring to.
This means we can't security-support non-PCI-Express devices with RMRRs
(if such exist in practice) any longer; note that as of trhe 1st of the
two commits referenced below assigning them to DomU-s is unsupported
anyway.

Fixes: 8f41e481b485 ("VT-d: re-assign devices directly")
Fixes: 14dd241aad8a ("IOMMU/x86: use per-device page tables for quarantining")
Coverity ID: 1503784
Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>