Re: [libvirt] [RFC PATCH 0/9] Introduce mediate ops in vfio-pci

Hi: On 2019/12/5 上午11:24, Yan Zhao wrote: > For SRIOV devices, VFs are passthroughed into guest directly without host > driver mediation. However, when VMs migrating with passthroughed VFs, > dynamic host mediation is required to (1) get device states, (2) get > dirty pages. Since device states as well as other critical information > required for dirty page tracking for VFs are usually retrieved from PFs, > it is handy to provide an extension in PF driver to centralizingly control > VFs' migration. > > Therefore, in order to realize (1) passthrough VFs at normal time, (2) > dynamically trap VFs' bars for dirty page tracking and A silly question, what's the reason for doing this, is this a must for dirty page tracking?

> (3) centralizing > VF critical states retrieving and VF controls into one driver, we propose > to introduce mediate ops on top of current vfio-pci device driver. > > > _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ > __________ register mediate ops| ___________ ___________ | > | |<-----------------------| VF | | | > | vfio-pci | | | mediate | | PF driver | | > |__________|----------------------->| driver | |___________| > | open(pdev) | ----------- | | > | | > | |_ _ _ _ _ _ _ _ _ _ _ _|_ _ _ _ _| > \|/ \|/ > ----------- ------------ > | VF | | PF | > ----------- ------------ > > > VF mediate driver could be a standalone driver that does not bind to > any devices (as in demo code in patches 5-6) or it could be a built-in > extension of PF driver (as in patches 7-9) . > > Rather than directly bind to VF, VF mediate driver register a mediate > ops into vfio-pci in driver init. vfio-pci maintains a list of such > mediate ops. > (Note that: VF mediate driver can register mediate ops into vfio-pci > before vfio-pci binding to any devices. And VF mediate driver can > support mediating multiple devices.) > > When opening a device (e.g. a VF), vfio-pci goes through the mediate ops > list and calls each vfio_pci_mediate_ops->open() with pdev of the opening > device as a parameter. > VF mediate driver should return success or failure depending on it > supports the pdev or not. > E.g. VF mediate driver would compare its supported VF devfn with the > devfn of the passed-in pdev. > Once vfio-pci finds a successful vfio_pci_mediate_ops->open(), it will > stop querying other mediate ops and bind the opening device with this > mediate ops using the returned mediate handle. > > Further vfio-pci ops (VFIO_DEVICE_GET_REGION_INFO ioctl, rw, mmap) on the > VF will be intercepted into VF mediate driver as > vfio_pci_mediate_ops->get_region_info(), > vfio_pci_mediate_ops->rw, > vfio_pci_mediate_ops->mmap, and get customized. > For vfio_pci_mediate_ops->rw and vfio_pci_mediate_ops->mmap, they will > further return 'pt' to indicate whether vfio-pci should further > passthrough data to hw. > > when vfio-pci closes the VF, it calls its vfio_pci_mediate_ops->release() > with a mediate handle as parameter. > > The mediate handle returned from vfio_pci_mediate_ops->open() lets VF > mediate driver be able to differentiate two opening VFs of the same device > id and vendor id. > > When VF mediate driver exits, it unregisters its mediate ops from > vfio-pci. > > > In this patchset, we enable vfio-pci to provide 3 things: > (1) calling mediate ops to allow vendor driver customizing default > region info/rw/mmap of a region. > (2) provide a migration region to support migration What's the benefit of introducing a region? It looks to me we don't expect the region to be accessed directly from guest. Could we simply extend device fd ioctl for doing such things?

> (3) provide a dynamic trap bar info region to allow vendor driver > control trap/untrap of device pci bars > > This vfio-pci + mediate ops way differs from mdev way in that > (1) medv way needs to create a 1:1 mdev device on top of one VF, device > specific mdev parent driver is bound to VF directly. > (2) vfio-pci + mediate ops way does not create mdev devices and VF > mediate driver does not bind to VFs. Instead, vfio-pci binds to VFs. > > The reason why we don't choose the way of writing mdev parent driver is > that > (1) VFs are almost all the time directly passthroughed. Directly binding > to vfio-pci can make most of the code shared/reused. Can we split out the common parts from vfio-pci?

> If we write a > vendor specific mdev parent driver, most of the code (like passthrough > style of rw/mmap) still needs to be copied from vfio-pci driver, which is > actually a duplicated and tedious work. The mediate ops looks quite similar to what vfio-mdev did. And it looks to me we need to consider live migration for mdev as well. In that case, do we still expect mediate ops through VFIO directly? > (2) For features like dynamically trap/untrap pci bars, if they are in > vfio-pci, they can be available to most people without repeated code > copying and re-testing. > (3) with a 1:1 mdev driver which passthrough VFs most of the time, people > have to decide whether to bind VFs to vfio-pci or mdev parent driver before > it runs into a real migration need. However, if vfio-pci is bound > initially, they have no chance to do live migration when there's a need > later. We can teach management layer to do this.

Thanks > > In this patchset, > - patches 1-4 enable vfio-pci to call mediate ops registered by vendor > driver to mediate/customize region info/rw/mmap. > > - patches 5-6 provide a standalone sample driver to register a mediate ops > for Intel Graphics Devices. It does not bind to IGDs directly but decides > what devices it supports via its pciidlist. It also demonstrates how to > dynamic trap a device's PCI bars. (by adding more pciids in its > pciidlist, this sample driver actually is not necessarily limited to > support IGDs) > > - patch 7-9 provide a sample on i40e driver that supports Intel(R) > Ethernet Controller XL710 Family of devices. It supports VF precopy live > migration on Intel's 710 SRIOV. (but we commented out the real > implementation of dirty page tracking and device state retrieving part > to focus on demonstrating framework part. Will send out them in future > versions) > patch 7 registers/unregisters VF mediate ops when PF driver > probes/removes. It specifies its supporting VFs via > vfio_pci_mediate_ops->open(pdev) > > patch 8 reports device cap of VFIO_PCI_DEVICE_CAP_MIGRATION and > provides a sample implementation of migration region. > The QEMU part of vfio migration is based on v8 > https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg05542.html. > We do not based on recent v9 because we think there are still opens in > dirty page track part in that series. > > patch 9 reports device cap of VFIO_PCI_DEVICE_CAP_DYNAMIC_TRAP_BAR and > provides an example on how to trap part of bar0 when migration starts > and passthrough this part of bar0 again when migration fails. > > Yan Zhao (9): > vfio/pci: introduce mediate ops to intercept vfio-pci ops > vfio/pci: test existence before calling region->ops > vfio/pci: register a default migration region > vfio-pci: register default dynamic-trap-bar-info region > samples/vfio-pci/igd_dt: sample driver to mediate a passthrough IGD > sample/vfio-pci/igd_dt: dynamically trap/untrap subregion of IGD bar0 > i40e/vf_migration: register mediate_ops to vfio-pci > i40e/vf_migration: mediate migration region > i40e/vf_migration: support dynamic trap of bar0 > > drivers/net/ethernet/intel/Kconfig | 2 +- > drivers/net/ethernet/intel/i40e/Makefile | 3 +- > drivers/net/ethernet/intel/i40e/i40e.h | 2 + > drivers/net/ethernet/intel/i40e/i40e_main.c | 3 + > .../ethernet/intel/i40e/i40e_vf_migration.c | 626 ++++++++++++++++++ > .../ethernet/intel/i40e/i40e_vf_migration.h | 78 +++ > drivers/vfio/pci/vfio_pci.c | 189 +++++- > drivers/vfio/pci/vfio_pci_private.h | 2 + > include/linux/vfio.h | 18 + > include/uapi/linux/vfio.h | 160 +++++ > samples/Kconfig | 6 + > samples/Makefile | 1 + > samples/vfio-pci/Makefile | 2 + > samples/vfio-pci/igd_dt.c | 367 ++++++++++ > 14 files changed, 1455 insertions(+), 4 deletions(-) > create mode 100644 drivers/net/ethernet/intel/i40e/i40e_vf_migration.c > create mode 100644 drivers/net/ethernet/intel/i40e/i40e_vf_migration.h > create mode 100644 samples/vfio-pci/Makefile > create mode 100644 samples/vfio-pci/igd_dt.c >