virtio-gpu: handle partial maps properly

virtio-gpu: handle partial maps properly

dma_memory_map() may map only a part of the request.  Happens if the
request can't be mapped in one go, for example due to a iommu creating
a linear dma mapping for scattered physical pages.  Should that be the
case virtio-gpu must call dma_memory_map() again with the remaining
range instead of simply throwing an error.

Note that this change implies the number of iov entries may differ from
the number of mapping entries sent by the guest.  Therefore the iov_len
bookkeeping needs some updates too, we have to explicitly pass around
the iov length now.

Reported-by: Auger Eric <eric.auger@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20210506091001.1301250-1-kraxel@redhat.com
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20210506091001.1301250-1-kraxel@redhat.com>