On Tue, 24 May 2022 14:18:35 +0800 Lei Rao <lei....@intel.com> wrote:
> Migration of a VFIO passthrough device can be supported by using a device > specific kernel driver to save/restore the device state thru device specific > interfaces. But this approach doesn't work for devices that lack a state > migration interface, e.g. NVMe. > > On the other hand, Infrastructure Process Unit (IPU) or Data Processing Unit > (DPU) vendors may choose to implement an out-of-band interface from the SoC > to > help manage the state of such non-migratable devices e.g. via gRPC or > JSON-RPC > protocols. > > This RFC attempts to support such out-of-band migration interface by > introducing > the concept of migration backends in vfio. The existing logic around vfio > migration uAPI is now called the 'local' backend while a new 'out-of-band' > backend is further introduced allowing vfio to redirect VMState ops to an > external plugin. > > Currently, the backend migration Ops is defined close to SaveVMHandlers. We > also > considered whether there is value of abstracting it in a lower level e.g. > close > to vfio migration uAPI but no clear conclusion. Hence this is one part which > we'd like to hear suggestions. > > This proposal adopts a plugin mechanism (an example can be found in [1]) > given > that IPU/DPU vendors usually implement proprietary migration interfaces > without > a standard. But we are also open if an alternative option makes better sense, > e.g. via loadable modules (with Qemu supporting gRPC or JSON-RPC support) or > an > IPC mechanism similar to vhost-user. AFAIU, QEMU is not interested in supporting plugin modules, especially proprietary ones. I don't see that a case has really been made that this cannot be done in-band, through a vfio-pci variant driver, possibly making use of proprietary interfaces to a userspace agent if necessary (though please don't ask such to be accepted in-tree for the kernel either). A vfio-user device server might also host such proprietary, device specific agents while supporting the standard, in-band migration interface. Thanks, Alex > > The following graph describes the overall component relationship: > > +----------------------------------------------------+ > | QEMU | > | +------------------------------------------------+ | > | | VFIO Live Migration Framework | | > | | +--------------------------------------+ | | > | | | VFIOMigrationOps | | | > | | +-------^---------------------^--------+ | | > | | | | | | > | | +-------v-------+ +-------v--------+ | | > | | | LM Backend Via| | LM Backend Via | | | > | | | Device Fd | | Plugins | | | > | | +-------^-------+ | +----------+ | | > | | | | |Plugin Ops+----+-+------------+ > | | | +-----+----------+ | | | > | | | | | > +---------v----------+ > | +------------+-----------------------------------+ | | Vendor Specific > | > | | | | Plugins(.so) > | > +--------------+-------------------------------------+ > +----------+---------+ > UserSpace | | > ----------------+--------------------------------------------- | > Kernel | | > | | > +----------v----------------------+ | > | Kernel VFIO Driver | | > | +-------------------------+ | | > | | | | | Network > | | Vendor-Specific Driver | | | > | | | | | > | +----------^--------------+ | | > | | | | > +---------------+-----------------+ | > | | > | | > ---------------------+----------------------------------------- | > Hardware | | > | +-----+-----+-----+----+-----+ | > +----------v------+ | VF0 | VF1 | VF2 | ...| VFn | | > | Traditional | +-----+-----+-----+----+-----+ | > | PCIe Devices | | | | > +-----------------+ | +--------+------------+ | | > | | | Agent |<-+----+ > | | +------------+ | > | | | | > | | SOC | | > | +---------------------+ | > | IPU | > +----------------------------+ > > Two command-line parameters (x-plugin-path and x-plugin-arg) are introduced > to > enable the out-of-band backend. If specified, vfio will attempt to use the > out-of-band backend. > > The following is an example of VFIO command-line parameters for OOB-Approach: > > -device > vfio-pci,id=$ID,host=$bdf,x-enable-migration,x-plugin-path=$plugin_path,x-plugin-arg=$plugin_arg > > [1] https://github.com/raolei-intel/vfio-lm-plugin-example.git > > Lei Rao (13): > vfio/migration: put together checks of migration initialization > conditions > vfio/migration: move migration struct allocation out of > vfio_migration_init > vfio/migration: move vfio_get_dev_region_info out of > vfio_migration_probe > vfio/migration: Separated functions that relate to the In-Band > approach > vfio/migration: rename functions that relate to the In-Band approach > vfio/migration: introduce VFIOMigrationOps layer in VFIO live > migration framework > vfio/migration: move the statistics of bytes_transferred to generic > VFIO migration layer > vfio/migration: split migration handler registering from > vfio_migration_init > vfio/migration: move the functions of In-Band approach to a new file > vfio/pci: introduce command-line parameters to specify migration > method > vfio/migration: add a plugin layer to support out-of-band live > migration > vfio/migration: add some trace-events for vfio migration plugin > vfio/migration: make the region and plugin member of struct > VFIOMigration to be a union > > docs/devel/vfio-migration-plugin.rst | 165 +++++++ > hw/vfio/meson.build | 2 + > hw/vfio/migration-local.c | 456 +++++++++++++++++++ > hw/vfio/migration-plugin.c | 266 +++++++++++ > hw/vfio/migration.c | 577 ++++++------------------ > hw/vfio/pci.c | 2 + > hw/vfio/trace-events | 9 +- > include/hw/vfio/vfio-common.h | 37 +- > include/hw/vfio/vfio-migration-plugin.h | 21 + > 9 files changed, 1096 insertions(+), 439 deletions(-) > create mode 100644 docs/devel/vfio-migration-plugin.rst > create mode 100644 hw/vfio/migration-local.c > create mode 100644 hw/vfio/migration-plugin.c > create mode 100644 include/hw/vfio/vfio-migration-plugin.h >
