[Qemu-devel] [PATCH V3 0/4] vfio: Introduce Live migration capability to vfio_mdev device

[Yulei Zhang]

Summary

This series RFC would like to resume the discussion about how to
introduce the live migration capability to vfio mdev device. 

By adding a new vfio subtype region VFIO_REGION_SUBTYPE_DEVICE_STATE,
the mdev device will be set to migratable if the new region exist
during the initialization.  

The intention to add the new region is using it for mdev device status
save and restore during the migration. The access to this region
will be trapped and forward to the mdev device driver, it also uses 
the first byte in the new region to control the running state of mdev
device, so during the migration after stop the mdev driver, qemu could
retrieve the specific device status from this region and transfer to 
the target VM side for the mdev device restore.

In addition,  we add one new ioctl VFIO_IOMMU_GET_DIRTY_BITMAP to help do 
the mdev device dirty page synchronization during the migration, currently
it is just for static copy, in the future we would like to add new interface
for the pre-copy.

Below is the vfio_mdev device migration sequence
Source VM side:
                        start migration
                                |
                                V
                 get the cpu state change callback, write to the
                 subregion's first byte to stop the mdev device
                                |
                                V
                 quary the dirty page bitmap from iommu container 
                 and add into qemu dirty list for synchronization
                                |
                                V
                 save the deivce status into Qemufile which is 
                     read from the vfio device subregion

Target VM side:
                   restore the mdev device after get the
                     saved status context from Qemufile
                                |
                                V
                     get the cpu state change callback
                     write to subregion's first byte to 
                      start the mdev device to put it in 
                      running status
                                |
                                V
                        finish migration

V3->V2:
1. rebase the patch to Qemu stable 2.10 branch.
2. use a common name for the subregion instead of specific for 
   intel IGD.

V1->V2:
Per Alex's suggestion:
1. use device subtype region instead of VFIO PCI fixed region.
2. remove unnecessary ioctl, use the first byte of subregion to 
   control the running state of mdev device.  
3. for dirty page synchronization, implement the interface with
   VFIOContainer instead of vfio pci device.

Yulei Zhang (4):
  vfio: introduce a new VFIO subregion for mdev device migration support
  vfio: Add vm status change callback to stop/restart the mdev device
  vfio: Add struct vfio_vmstate_info to introduce put/get callback
    funtion for vfio device status save/restore
  vifo: introduce new VFIO ioctl VFIO_IOMMU_GET_DIRTY_BITMAP

 hw/vfio/common.c              |  34 +++++++++
 hw/vfio/pci.c                 | 171 +++++++++++++++++++++++++++++++++++++++++-
 hw/vfio/pci.h                 |   1 +
 include/hw/vfio/vfio-common.h |   1 +
 linux-headers/linux/vfio.h    |  29 ++++++-
 5 files changed, 232 insertions(+), 4 deletions(-)

-- 
2.7.4