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Thu, 23 Apr 2026 14:23:19 -0700 (PDT) Date: Thu, 23 Apr 2026 21:23:04 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.54.0.rc2.544.gc7ae2d5bb8-goog Message-ID: <20260423212316.3431746-1-dmatlack@google.com> Subject: [PATCH v4 00/11] PCI: liveupdate: PCI core support for Live Update From: David Matlack To: iommu@lists.linux.dev, kexec@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pci@vger.kernel.org Cc: Adithya Jayachandran , Alexander Graf , Alex Williamson , Bjorn Helgaas , Chris Li , David Matlack , David Rientjes , Jacob Pan , Jason Gunthorpe , Joerg Roedel , Jonathan Corbet , Josh Hilke , Leon Romanovsky , Lukas Wunner , Mike Rapoport , Parav Pandit , Pasha Tatashin , Pranjal Shrivastava , Pratyush Yadav , Robin Murphy , Saeed Mahameed , Samiullah Khawaja , Shuah Khan , Will Deacon , William Tu , Yi Liu Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260423_142321_392095_5AEF5B73 X-CRM114-Status: GOOD ( 25.09 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org This series can be found on GitHub: https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v4 This patch 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. This series was split off from the the VFIO driver series [1] to enable more rapid iteration on the PCI core changes, add breathing room to split changes into smaller patches, and add some more functionality. 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 "outgoing" devices for preservation and for the PCI core to identify "incoming" preserved devices during enumeration. 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. Inherit secondary/subordinate bus numbers, ARI Forwarding Enable, and Access Control Services (ACS) flags from the previous kernel to ensure a stable routing fabric and consistent IOMMU group assignments during Live Update. 5. Restrict preservation to devices in immutable singleton IOMMU groups. Require that all upstream bridges have the necessary ACS features enabled to prevent IOMMU group changes across the update. 6. Modify the PCI shutdown path to avoid disabling bus mastering on preserved devices and their upstream bridges, allowing memory transactions to continue uninterrupted. 7. Provide comprehensive documentation for the FLB API, device tracking mechanisms, and the division of responsibilities between the PCI core, drivers, and userspace. This series could be simplified down to fewer patches by limiting preservation support to only devices on a root bus. Supporting devices downstream of bridges could be split off into a follow-up series. However since I got bridge preservation working and the series was less than 15 patches I opted to include it for now. Dependencies ------------ This series depends on 2 LUO patches to enable refcounting of the incoming FLB so that it is safe for the PCI core to use liveupdate_flb_get_incoming() during enumeration. https://lore.kernel.org/lkml/20260423174032.3140399-1-dmatlack@google.com/ VFIO support for PCI device preservation is built on top of this series. The following branch on GitHub contains all the patches together to enable testing (the LUO FLB changes, this series, and the VFIO patches): https://github.com/dmatlack/linux/tree/liveupdate/pci/base/v4-with-vfio Testing ------- This series was tested in combination with the VFIO patches mentioned in the previous section using the the new VFIO selftests: - vfio_pci_liveupdate_uapi_test - vfio_pci_liveupdate_kexec_test Both tests were ran in ran in a QEMU-based VM environment, using a single virtio-net PCIe device behind a PCI-to-PCI bridge as the test device, and in a baremetal environment on an Intel EMR server, using 8x Intel DSA PCIe devices (each on a host bridge). Future Work ----------- After this series we expect to make further improvements to the PCI core support for Live Update. Once these are done we plan to drop the "experimental" verbiage from PCI_LIVEUPDATE Kconfig help message and documentation. - Ensure bridges with downstream preserved devices stay in D0 across Live Update in case preserved endpoints are doing memory transactions. - Preserve BARs of all preserved devices to avoid disrupting P2P Beyond that we also plan to add support for preserving Virtual Functions since that is a major use-case for Cloud environments. This will require keeping SR-IOV enabled on the partent PF across a Live Update. Changelog --------- v4: Enhancements on top of previous series: - Split "PCI: Add API to track PCI devices preserved across Live Update" from v3 into 4 separate commits to make reviewing easier (FLB setup, outgoing device tracking, incoming device tracking, and documentation for driver binding) - Use new incoming FLB refcounting to avoid use-after-free bugs during enumeration - Use an xarray to speed up looking up of incoming preserved devices during enumeration - Use a per-device bit to indicate when secondary and subordinate bus numbers should be inherited on bridges instead of global data to avoid races between the 2 passes - Inherit ARI enablement across Live Update - Automatically preserve bridges upstream of preserved endpoints so so that ACS flags, ARI enablement, and bus mastering can be kept constant on bridges across Live Update - Avoid clearing bus mastering during shutdown on outgoing preserved device to avoid disrupting memory transcations being performed by preserved devices - Add a MAINTAINERS entry for the new files to support Live Update in the PCI core - Add info and debug level logging for various events throughout device preservation Changes based on review feedback on v3: - Fix up typos, wording, documentation gaps, and code style (Bjorn) - Use pci_WARN_ONCE() where possible (Bjorn) - Require ACS flags to preserve devices behind bridges so that singleton IOMMU group topology is guaranteed to remain across Live Update (Yi) - Preserve ACS flags (Jason, Alex) 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/ [1] https://lore.kernel.org/kvm/20260323235817.1960573-1-dmatlack@google.com/ David Matlack (11): 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: Inherit bus numbers during Live Update PCI: liveupdate: Auto-preserve upstream bridges across Live Update PCI: liveupdate: Inherit ACS flags in incoming preserved devices PCI: liveupdate: Require preserved devices are in immutable singleton IOMMU groups PCI: liveupdate: Inherit ARI Forwarding Enable on preserved bridges 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 | 23 + .../admin-guide/kernel-parameters.txt | 6 +- Documentation/core-api/liveupdate.rst | 1 + MAINTAINERS | 13 + drivers/iommu/iommu.c | 35 ++ drivers/pci/Kconfig | 14 + drivers/pci/Makefile | 1 + drivers/pci/liveupdate.c | 562 ++++++++++++++++++ drivers/pci/pci-driver.c | 31 +- drivers/pci/pci.c | 22 +- drivers/pci/pci.h | 13 + drivers/pci/probe.c | 25 +- include/linux/iommu.h | 7 + include/linux/kho/abi/pci.h | 62 ++ include/linux/pci.h | 58 ++ 16 files changed, 858 insertions(+), 16 deletions(-) create mode 100644 Documentation/PCI/liveupdate.rst create mode 100644 drivers/pci/liveupdate.c create mode 100644 include/linux/kho/abi/pci.h base-commit: a13f7eb5b2d5bef886659768680093bec1c0470d -- 2.54.0.rc2.544.gc7ae2d5bb8-goog