vhost: Allow adjoining regions

My rework of section adding combines overlapping or adjoining regions,
but checks they're actually the same underlying RAM block.
Fix the case where two blocks adjoin but don't overlap; that new region
should get added (but not combined), but my previous patch was disallowing it.

Fixes: c1ece84e7c9

Reported-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Tested-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index b6c314e..a21a5a2 100644 (file)
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -595,10 +595,15 @@ static void vhost_region_add_section(struct vhost_dev *dev,
                                         prev_sec->offset_within_address_space,
                                         prev_sec->offset_within_region);
             } else {
-                error_report("%s: Overlapping but not coherent sections "
-                             "at %"PRIx64,
-                             __func__, mrs_gpa);
-                return;
+                /* adjoining regions are fine, but overlapping ones with
+                 * different blocks/offsets shouldn't happen
+                 */
+                if (mrs_gpa != prev_gpa_end + 1) {
+                    error_report("%s: Overlapping but not coherent sections "
+                                 "at %"PRIx64,
+                                 __func__, mrs_gpa);
+                    return;
+                }
             }
         }
     }