Re: [PATCH V4 12/43] vfio/container: restore DMA vaddr

[Cédric Le Goater]

On 5/29/25 21:24, Steve Sistare wrote:

In new QEMU, do not register the memory listener at device creation time.
Register it later, in the container post_load handler, after all vmstate
that may affect regions and mapping boundaries has been loaded.  The
post_load registration will cause the listener to invoke its callback on
each flat section, and the calls will match the mappings remembered by the
kernel.

The listener calls a special dma_map handler that passes the new VA of each
section to the kernel using VFIO_DMA_MAP_FLAG_VADDR.  Restore the normal
handler at the end.

Signed-off-by: Steve Sistare <steven.sist...@oracle.com>

Reviewed-by: Cédric Le Goater <c...@redhat.com>

Thanks,

C.

---
  include/hw/vfio/vfio-cpr.h |  3 +++
  hw/vfio/container.c        | 15 ++++++++++--
  hw/vfio/cpr-legacy.c       | 57 ++++++++++++++++++++++++++++++++++++++++++++++
  3 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/include/hw/vfio/vfio-cpr.h b/include/hw/vfio/vfio-cpr.h
index 5a2e5f6..0462447 100644
--- a/include/hw/vfio/vfio-cpr.h
+++ b/include/hw/vfio/vfio-cpr.h
@@ -17,6 +17,9 @@ struct VFIOGroup;

typedef struct VFIOContainerCPR {

      Error *blocker;
+    int (*saved_dma_map)(const struct VFIOContainerBase *bcontainer,
+                         hwaddr iova, ram_addr_t size,
+                         void *vaddr, bool readonly, MemoryRegion *mr);
  } VFIOContainerCPR;

diff --git a/hw/vfio/container.c b/hw/vfio/container.c

index 798abda..f91f2d5 100644
--- a/hw/vfio/container.c
+++ b/hw/vfio/container.c
@@ -137,6 +137,8 @@ static int vfio_legacy_dma_unmap_one(const 
VFIOContainerBase *bcontainer,
      int ret;
      Error *local_err = NULL;

+ g_assert(!cpr_is_incoming());

+
      if (iotlb && vfio_container_dirty_tracking_is_started(bcontainer)) {
          if (!vfio_container_devices_dirty_tracking_is_supported(bcontainer) &&
              bcontainer->dirty_pages_supported) {
@@ -691,8 +693,17 @@ static bool vfio_container_connect(VFIOGroup *group, 
AddressSpace *as,
      }
      group_was_added = true;

- if (!vfio_listener_register(bcontainer, errp)) {

-        goto fail;
+    /*
+     * If CPR, register the listener later, after all state that may
+     * affect regions and mapping boundaries has been cpr load'ed.  Later,
+     * the listener will invoke its callback on each flat section and call
+     * dma_map to supply the new vaddr, and the calls will match the mappings
+     * remembered by the kernel.
+     */
+    if (!cpr_is_incoming()) {
+        if (!vfio_listener_register(bcontainer, errp)) {
+            goto fail;
+        }
      }

bcontainer->initialized = true;

diff --git a/hw/vfio/cpr-legacy.c b/hw/vfio/cpr-legacy.c
index cf80332..512ef41 100644
--- a/hw/vfio/cpr-legacy.c
+++ b/hw/vfio/cpr-legacy.c
@@ -10,11 +10,13 @@
  #include "hw/vfio/vfio-container.h"
  #include "hw/vfio/vfio-cpr.h"
  #include "hw/vfio/vfio-device.h"
+#include "hw/vfio/vfio-listener.h"
  #include "migration/blocker.h"
  #include "migration/cpr.h"
  #include "migration/migration.h"
  #include "migration/vmstate.h"
  #include "qapi/error.h"
+#include "qemu/error-report.h"

static bool vfio_dma_unmap_vaddr_all(VFIOContainer *container, Error **errp)

  {
@@ -31,6 +33,32 @@ static bool vfio_dma_unmap_vaddr_all(VFIOContainer 
*container, Error **errp)
      return true;
  }

+/*

+ * Set the new @vaddr for any mappings registered during cpr load.
+ * The incoming state is cleared thereafter.
+ */
+static int vfio_legacy_cpr_dma_map(const VFIOContainerBase *bcontainer,
+                                   hwaddr iova, ram_addr_t size, void *vaddr,
+                                   bool readonly, MemoryRegion *mr)
+{
+    const VFIOContainer *container = container_of(bcontainer, VFIOContainer,
+                                                  bcontainer);
+    struct vfio_iommu_type1_dma_map map = {
+        .argsz = sizeof(map),
+        .flags = VFIO_DMA_MAP_FLAG_VADDR,
+        .vaddr = (__u64)(uintptr_t)vaddr,
+        .iova = iova,
+        .size = size,
+    };
+
+    g_assert(cpr_is_incoming());
+
+    if (ioctl(container->fd, VFIO_IOMMU_MAP_DMA, &map)) {
+        return -errno;
+    }
+
+    return 0;
+}

static bool vfio_cpr_supported(VFIOContainer *container, Error **errp)

  {
@@ -59,11 +87,34 @@ static int vfio_container_pre_save(void *opaque)
      return 0;
  }

+static int vfio_container_post_load(void *opaque, int version_id)

+{
+    VFIOContainer *container = opaque;
+    VFIOContainerBase *bcontainer = &container->bcontainer;
+    VFIOGroup *group;
+    Error *local_err = NULL;
+
+    if (!vfio_listener_register(bcontainer, &local_err)) {
+        error_report_err(local_err);
+        return -1;
+    }
+
+    QLIST_FOREACH(group, &container->group_list, container_next) {
+        VFIOIOMMUClass *vioc = VFIO_IOMMU_GET_CLASS(bcontainer);
+
+        /* Restore original dma_map function */
+        vioc->dma_map = container->cpr.saved_dma_map;
+    }
+    return 0;
+}
+
  static const VMStateDescription vfio_container_vmstate = {
      .name = "vfio-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_incoming_needed,
      .fields = (VMStateField[]) {
          VMSTATE_END_OF_LIST()
@@ -86,6 +137,12 @@ bool vfio_legacy_cpr_register_container(VFIOContainer 
*container, Error **errp)

vmstate_register(NULL, -1, &vfio_container_vmstate, container); + /* During incoming CPR, divert calls to dma_map. */

+    if (cpr_is_incoming()) {
+        VFIOIOMMUClass *vioc = VFIO_IOMMU_GET_CLASS(bcontainer);
+        container->cpr.saved_dma_map = vioc->dma_map;
+        vioc->dma_map = vfio_legacy_cpr_dma_map;
+    }
      return true;
  }