Re: [PATCH v9 00/13] PCI: liveupdate: PCI core support for Live Update

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2026/9/18 13:06, David Matlack 写道:
> This series can be found on GitHub:
> 
>    https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v9
> 
> This series introduces support in the PCI core for Live Update, enabling
> drivers to preserve PCI devices across a kexec-based kernel update
> without interrupting the device. This functionality is critical for
> minimizing downtime in environments where PCI devices (e.g., those
> assigned to VMs via VFIO) must continue operating or maintain state
> across a host kernel upgrade.
> 
> Specifically, this series allows preserved PCI devices to perform
> uninterrupted memory transactions (DMA) targeting system memory
> (specifically, preserved memfds) across a Live Update. These devices can
> be behind a bridge but must not be VFs. Support for P2P and VF
> preservation will be addressed in future series.
> 
> Series Overview
> ---------------
> 
> This series implements the following to support PCI device preservation
> across Live Update:
> 
>    1. Set up a File-Lifecycle-Bound (FLB) handler to track and preserve
>       PCI-specific state (struct pci_ser) across Live Update using Kexec
>       Handover (KHO).
> 
>    2. Add APIs for drivers to register devices for preservation
>       (outgoing) and for the PCI core to identify preserved devices
>       during enumeration (incoming)
> 
>    3. Automatically preserve all upstream bridges for any preserved
>       endpoint. Use reference counting to ensure bridges remain preserved
>       as long as any downstream device is preserved.
> 
>    4. Guarantee that preserved devices retain the same RequesterID (bus,
>       device, function) for the duration of their preservation by
>       inheriting secondary bus numbers, subordinate bus numbers, and ARI
>       Forwarding Enable on preserved bridges.
> 
>    5. Guarantee that memory transactions to/from preserved devices are
>       routed consistently by inheriting Access Control Services (ACS)
>       flags across a Live Update, from the endpoint up to the root port.
> 
>    6. Modify the PCI shutdown path to avoid disabling bus mastering on
>       preserved devices, thereby allowing preserved devices to perform
>       uninterrupted during kexec for Live Update.
> 
>    7. Provide comprehensive documentation for the FLB API, device
>       tracking mechanisms, and the division of responsibilities between
>       the PCI core, drivers, and userspace.
> 
> Merge Plan
> ----------
> 
> This series will be merged through liveupdate.git, matching the
> agreed-upon tree in the MAINTAINERS entry for PCI LIVE UPDATE.
> 
> Testing
> -------
> 
> This series was tested in conjunction with v5 of the VFIO PCI driver
> series:
> 
>    https://lore.kernel.org/kvm/20260714151505.3466855-1-vipinsh@google.com/
> 
> The full set of patches used for testing can be found on GitHub.
> 
>    https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v9-with-vfio
> 
> Testing was performed using the new VFIO selftests:
> 
>    - vfio_pci_liveupdate_uapi_test
>    - vfio_pci_liveupdate_kexec_test

With this vfio_pci_liveupdate_kexec_test based on this patchset v9, I 
have made tests in my local kvm. It worked as expected.

Yanjun Zhu

> 
> Both tests were run in a QEMU-based VM environment (using a single
> virtio-net PCIe device connected to a root port to exercise bridge
> support) and on bare metal using an Intel EMR server with 8x Intel DSA
> PCIe devices and 1x NVMe device.
> 
> Future Work
> -----------
> 
> Following this series, we expect to make further improvements to the PCI
> core support for Live Update:
> 
>    - Allow P2P across Live Update by avoiding resizing or moving
>      preserved device BARs and preserving all upstream bridge windows.
> 
>    - Support preserving Virtual Functions by preserving SR-IOV
>      configuration on PFs and enumerating VFs after Live Update.
> 
> Changelog
> ---------
> 
> v9:
>   - Simplify pci_liveupdate_preserve_bus_numbers() to always return true
>     if a device was preserved and drop pci_liveupdate_scan_bridge_end()
>     (Bjorn)
>   - Add pci_liveupdate_refuse_bus_numbers() to determine when it is safe
>     for the PCI core to assign bus numbers to unconfigured bridges. This
>     required moving "Auto-preserve upstream bridges across Live Update"
>     before "Preserve bus numbers during Live Update" (Bjorn)
>   - Add "PCI: Save and restore the ACS Control register" so that the ACS
>     Control register is handled by the normal save/restore path (Bjorn)
>   - Rename struct pci_liveupdate::was_preserved to was_incoming, to
>     disambiguate incoming from outgoing preservation (me)
>   - Log unfinished preserved devices from the incoming FLB rather than
>     by walking struct pci_dev (Sashiko)
>   - Document that state handed over by the previous kernel is trusted,
>     and panic in pci_flb_retrieve() where failures are detected rather
>     than unwinding into a caller that panics anyway (Sashiko)
>   - Fall back to programming ACS from scratch when a preserved device has
>     no ACS save buffer, since there is nowhere to record the adopted
>     controls and they would be lost by the first reset (Sashiko)
>   - Drop Reviewed-by tags from "Preserve bus numbers during Live Update"
>     and "Adopt ACS controls in incoming preserved devices", both of which
>     changed materially since v8
>   - Extend commit messages and kernel-doc comments to make the FLB code
>     flow more clear (Bjorn)
>   - Address various spelling, formatting, and stylistic issues (Bjorn)
> 
> v8: https://lore.kernel.org/linux-pci/20260728221007.2098560-1-dmatlack@google.com/
> v7: https://lore.kernel.org/linux-pci/20260710212616.1351130-1-dmatlack@google.com/
> v6: https://lore.kernel.org/linux-pci/20260522202410.3104264-1-dmatlack@google.com/
> v5: https://lore.kernel.org/linux-pci/20260512184846.119396-1-dmatlack@google.com/
> v4: https://lore.kernel.org/linux-pci/20260423212316.3431746-1-dmatlack@google.com/
> v3: https://lore.kernel.org/kvm/20260323235817.1960573-1-dmatlack@google.com/
> v2: https://lore.kernel.org/kvm/20260129212510.967611-1-dmatlack@google.com/
> v1: https://lore.kernel.org/kvm/20251126193608.2678510-1-dmatlack@google.com/
> rfc: https://lore.kernel.org/kvm/20251018000713.677779-1-vipinsh@google.com/
> 
> 
> David Matlack (13):
>    PCI: liveupdate: Set up FLB handler for the PCI core
>    PCI: liveupdate: Track outgoing preserved PCI devices
>    PCI: liveupdate: Track incoming preserved PCI devices
>    PCI: liveupdate: Document driver binding responsibilities
>    PCI: liveupdate: Auto-preserve upstream bridges across Live Update
>    PCI: liveupdate: Preserve bus numbers during Live Update
>    PCI: Refactor matching logic for pci_dev_acs_ops
>    PCI: Save and restore the ACS Control register
>    PCI: liveupdate: Adopt ACS controls in incoming preserved devices
>    PCI: liveupdate: Adopt ARI Forwarding Enable on preserved bridges
>    PCI: liveupdate: Freeze preservation status during shutdown
>    PCI: liveupdate: Do not disable bus mastering on preserved devices
>      during kexec
>    Documentation: PCI: Add documentation for Live Update
> 
>   Documentation/PCI/index.rst                   |    1 +
>   Documentation/PCI/liveupdate.rst              |   35 +
>   .../admin-guide/kernel-parameters.txt         |    7 +-
>   Documentation/core-api/liveupdate.rst         |    5 +
>   MAINTAINERS                                   |   15 +
>   drivers/pci/Kconfig                           |   15 +
>   drivers/pci/Makefile                          |    1 +
>   drivers/pci/liveupdate.c                      | 1015 +++++++++++++++++
>   drivers/pci/liveupdate.h                      |   62 +
>   drivers/pci/pci-driver.c                      |    9 +-
>   drivers/pci/pci.c                             |   79 +-
>   drivers/pci/pci.h                             |    5 +
>   drivers/pci/probe.c                           |   16 +-
>   drivers/pci/quirks.c                          |   58 +-
>   include/linux/kho/abi/pci.h                   |   66 ++
>   include/linux/pci.h                           |    7 +
>   include/linux/pci_liveupdate.h                |   72 ++
>   17 files changed, 1429 insertions(+), 39 deletions(-)
>   create mode 100644 Documentation/PCI/liveupdate.rst
>   create mode 100644 drivers/pci/liveupdate.c
>   create mode 100644 drivers/pci/liveupdate.h
>   create mode 100644 include/linux/kho/abi/pci.h
>   create mode 100644 include/linux/pci_liveupdate.h
> 
> 
> base-commit: 945d61765894dda2f0344de50cb1ade2e51b66fd