[V2,44/45] iommufd: preserve DMA mappings

Commit Message

Steven Sistare Feb. 14, 2025, 2:14 p.m. UTC

During cpr-transfer load in new QEMU, the vfio_memory_listener causes
spurious calls to map and unmap DMA regions, as devices are created and
the address space is built.  This memory was already already mapped by the
device in old QEMU, so suppress the map and unmap callbacks during CPR --
eg, if the reused flag is set.  The reused flag is cleared in the post_load
handler.

Signed-off-by: Steve Sistare <[e-mail]>
---
 backends/iommufd.c    | 8 ++++++++
 hw/vfio/cpr-iommufd.c | 1 +
 2 files changed, 9 insertions(+)

Patch

diff --git a/backends/iommufd.c b/backends/iommufd.c
index da90b21..dfcfd6b 100644
--- a/backends/iommufd.c
+++ b/backends/iommufd.c
@@ -209,6 +209,10 @@  int iommufd_backend_map_file_dma(IOMMUFDBackend *be, uint32_t ioas_id,
         .length = size,
     };
 
+    if (be->cpr_reused) {
+        return 0;
+    }
+
     if (!readonly) {
         map.flags |= IOMMU_IOAS_MAP_WRITEABLE;
     }
@@ -240,6 +244,10 @@  int iommufd_backend_unmap_dma(IOMMUFDBackend *be, uint32_t ioas_id,
         .length = size,
     };
 
+    if (be->cpr_reused) {
+        return 0;
+    }
+
     ret = ioctl(fd, IOMMU_IOAS_UNMAP, &unmap);
     /*
      * IOMMUFD takes mapping as some kind of object, unmapping
diff --git a/hw/vfio/cpr-iommufd.c b/hw/vfio/cpr-iommufd.c
index 92b101d..286597a 100644
--- a/hw/vfio/cpr-iommufd.c
+++ b/hw/vfio/cpr-iommufd.c
@@ -66,6 +66,7 @@  static const VMStateDescription vfio_container_vmstate = {
     .name = "vfio-iommufd-container",
     .version_id = 0,
     .minimum_version_id = 0,
+    .priority = MIG_PRI_LOW,   /* Must happen after devices and groups */
     .pre_save = vfio_container_pre_save,
     .post_load = vfio_container_post_load,
     .needed = cpr_needed_for_reuse,