[PATCH v9 00/13] PCI: liveupdate: PCI core support for Live Update
Zhu Yanjun
yanjun.zhu at linux.dev
Tue Sep 22 11:54:08 PDT 2026
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
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