vfio/migration: Add x-migration-load-config-after-iter VFIO property

This property allows configuring whether to start the config load only
after all iterables were loaded, during non-iterables loading phase.
Such interlocking is required for ARM64 due to this platform VFIO
dependency on interrupt controller being loaded first.

The property defaults to AUTO, which means ON for ARM, OFF for other
platforms.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Avihai Horon <avihaih@nvidia.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Link: https://lore.kernel.org/qemu-devel/0e03c60dbc91f9a9ba2516929574df605b7dfcb4.1752589295.git.maciej.szmigiero@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/docs/devel/migration/vfio.rst b/docs/devel/migration/vfio.rst
index 2d8e5ca9dd..dae3a98830 100644
--- a/docs/devel/migration/vfio.rst
+++ b/docs/devel/migration/vfio.rst
@@ -247,3 +247,9 @@ The multifd VFIO device state transfer is controlled by
 "x-migration-multifd-transfer" VFIO device property. This property defaults to
 AUTO, which means that VFIO device state transfer via multifd channels is
 attempted in configurations that otherwise support it.
+
+Some host platforms (like ARM64) require that VFIO device config is loaded only
+after all iterables were loaded, during non-iterables loading phase.
+Such interlocking is controlled by "x-migration-load-config-after-iter" VFIO
+device property, which in its default setting (AUTO) does so only on platforms
+that actually require it.