vfio/migration: Add x-migration-multifd-transfer VFIO property

This property allows configuring whether to transfer the particular device
state via multifd channels when live migrating that device.

It defaults to AUTO, which means that VFIO device state transfer via
multifd channels is attempted in configurations that otherwise support it.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/d6dbb326e3d53c7104d62c96c9e3dd64e1c7b940.1741124640.git.maciej.szmigiero@oracle.com
[ clg: Added documentation ]
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 17 insertions, 1 deletions

diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
index bfb9a72fa4..aacddc503b 100644
--- a/hw/vfio/migration-multifd.c
+++ b/hw/vfio/migration-multifd.c
@@ -476,18 +476,34 @@ bool vfio_multifd_transfer_supported(void)
 
 bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev)
 {
-    return false;
+    VFIOMigration *migration = vbasedev->migration;
+
+    return migration->multifd_transfer;
 }
 
 bool vfio_multifd_setup(VFIODevice *vbasedev, bool alloc_multifd, Error **errp)
 {
     VFIOMigration *migration = vbasedev->migration;
 
+    if (vbasedev->migration_multifd_transfer == ON_OFF_AUTO_AUTO) {
+        migration->multifd_transfer = vfio_multifd_transfer_supported();
+    } else {
+        migration->multifd_transfer =
+            vbasedev->migration_multifd_transfer == ON_OFF_AUTO_ON;
+    }
+
     if (!vfio_multifd_transfer_enabled(vbasedev)) {
         /* Nothing further to check or do */
         return true;
     }
 
+    if (!vfio_multifd_transfer_supported()) {
+        error_setg(errp,
+                   "%s: Multifd device transfer requested but unsupported in the current config",
+                   vbasedev->name);
+        return false;
+    }
+
     if (alloc_multifd) {
         assert(!migration->multifd);
         migration->multifd = vfio_multifd_new();