Re: [PATCH v10 00/13] PCI: liveupdate: PCI core support for Live Update

[Pasha Tatashin]

On 10-13 16:25, David Matlack wrote:
> This series can be found on GitHub:
> 
>   https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v10
> 
> 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@xxxxxxxxxx/
> 
> The full set of patches used for testing can be found on GitHub.
> 
>   https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v10-with-vfio
> 
> Testing was performed using the new VFIO selftests:
> 
>   - vfio_pci_liveupdate_uapi_test
>   - vfio_pci_liveupdate_kexec_test
> 
> 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
> -----------
> 
> Please see the PCI core Live Update Roadmap:
> 
>   https://lore.kernel.org/linux-pci/20261001232133.560284-1-dmatlack@xxxxxxxxxx/
> 
> Changelog
> ---------
> 
> v10:
>  - Save and restore the ACS Egress Control Vector along with the ACS
>    Control register, sizing the save buffer from the HwInit Egress
>    Control Vector Size field (Alex) and drop Bjorn's R-b tag
>  - Make CONFIG_PCI_LIVEUPDATE depend on 64BIT from the first patch
>    rather than adding the dependency later in the series (Pratyush,
>    Mike)
>  - Reword kernel-doc comments to read better in the HTML docs and
>    spell out "reference count" (Mike)
>  - Replace the version number at the start of struct pci_ser with
>    required_flags and optional_flags, and record the size of struct
>    pci_dev_ser, so that the PCI FLB ABI can be extended (LPC BoF)

Hi Bjorn,

I am planning to target this series for the 7.5 merge window through the 
liveupdate tree, as we previously agreed. However, there are still 6 
patches that lack an Acked-by from you. I believe you might have 
reviewed some of them before, but the tags were lost during subsequent 
refactoring. Could you please take another look at the following to make 
sure everything is in order for us to merge the series:

PCI: liveupdate: Set up FLB handler for the PCI core
PCI: liveupdate: Track incoming preserved PCI devices
PCI: liveupdate: Document driver binding responsibilities
PCI: liveupdate: Auto-preserve upstream bridges across Live Update
PCI: Save and restore the ACS Control register and Egress Control Vector
PCI: liveupdate: Adopt ACS controls in incoming preserved devices

Thanks!

-- 
Pasha