Re: [PATCH V4 17/43] vfio-pci: skip reset during cpr

[Cédric Le Goater]

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

Do not reset a vfio-pci device during CPR, and do not complain if the
kernel's PCI config space changes for non-emulated bits between the
vmstate save and load, which can happen due to ongoing interrupt activity.

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 |  2 ++
  hw/vfio/cpr.c              | 31 +++++++++++++++++++++++++++++++
  hw/vfio/pci.c              |  7 +++++++
  3 files changed, 40 insertions(+)

diff --git a/include/hw/vfio/vfio-cpr.h b/include/hw/vfio/vfio-cpr.h
index 56ede04..8bf85b9 100644
--- a/include/hw/vfio/vfio-cpr.h
+++ b/include/hw/vfio/vfio-cpr.h
@@ -52,4 +52,6 @@ void vfio_cpr_giommu_remap(struct VFIOContainerBase 
*bcontainer,
  bool vfio_cpr_ram_discard_register_listener(
      struct VFIOContainerBase *bcontainer, MemoryRegionSection *section);

+extern const VMStateDescription vfio_cpr_pci_vmstate;

+
  #endif /* HW_VFIO_VFIO_CPR_H */
diff --git a/hw/vfio/cpr.c b/hw/vfio/cpr.c
index 0e59612..fdbb58e 100644
--- a/hw/vfio/cpr.c
+++ b/hw/vfio/cpr.c
@@ -8,6 +8,8 @@
  #include "qemu/osdep.h"
  #include "hw/vfio/vfio-device.h"
  #include "hw/vfio/vfio-cpr.h"
+#include "hw/vfio/pci.h"
+#include "migration/cpr.h"
  #include "qapi/error.h"
  #include "system/runstate.h"

@@ -37,3 +39,32 @@ void vfio_cpr_unregister_container(VFIOContainerBase *bcontainer)

  {
      migration_remove_notifier(&bcontainer->cpr_reboot_notifier);
  }
+
+/*
+ * The kernel may change non-emulated config bits.  Exclude them from the
+ * changed-bits check in get_pci_config_device.
+ */
+static int vfio_cpr_pci_pre_load(void *opaque)
+{
+    VFIOPCIDevice *vdev = opaque;
+    PCIDevice *pdev = &vdev->pdev;
+    int size = MIN(pci_config_size(pdev), vdev->config_size);
+    int i;
+
+    for (i = 0; i < size; i++) {
+        pdev->cmask[i] &= vdev->emulated_config_bits[i];
+    }
+
+    return 0;
+}
+
+const VMStateDescription vfio_cpr_pci_vmstate = {
+    .name = "vfio-cpr-pci",
+    .version_id = 0,
+    .minimum_version_id = 0,
+    .pre_load = vfio_cpr_pci_pre_load,
+    .needed = cpr_incoming_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_END_OF_LIST()
+    }
+};
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 56e7fdd..840590c 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -30,6 +30,7 @@
  #include "hw/qdev-properties.h"
  #include "hw/qdev-properties-system.h"
  #include "migration/vmstate.h"
+#include "migration/cpr.h"
  #include "qobject/qdict.h"
  #include "qemu/error-report.h"
  #include "qemu/main-loop.h"
@@ -3345,6 +3346,11 @@ static void vfio_pci_reset(DeviceState *dev)
  {
      VFIOPCIDevice *vdev = VFIO_PCI_BASE(dev);

+ /* Do not reset the device during qemu_system_reset prior to cpr load */

+    if (cpr_is_incoming()) {
+        return;
+    }
+
      trace_vfio_pci_reset(vdev->vbasedev.name);

vfio_pci_pre_reset(vdev);

@@ -3521,6 +3527,7 @@ static void vfio_pci_dev_class_init(ObjectClass *klass, 
const void *data)
  #ifdef CONFIG_IOMMUFD
      object_class_property_add_str(klass, "fd", NULL, vfio_pci_set_fd);
  #endif
+    dc->vmsd = &vfio_cpr_pci_vmstate;
      dc->desc = "VFIO-based PCI device assignment";
      pdc->realize = vfio_realize;