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

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

(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

(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.

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.

(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.

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