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[34.145.75.25]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b103435561sm482994a91.3.2026.11.06.14.35.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2026 14:35:31 -0800 (PST) Date: Fri, 6 Nov 2026 22:35:27 +0000 From: Samiullah Khawaja To: Vipin Sharma Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-pci@vger.kernel.org, ajayachandra@nvidia.com, alex@shazbot.org, amastro@fb.com, ankita@nvidia.com, apopple@nvidia.com, bhelgaas@google.com, chrisl@kernel.org, christian.koenig@amd.com, corbet@lwn.net, dmatlack@google.com, graf@amazon.com, jacob.pan@linux.microsoft.com, jgg@nvidia.com, jgg@ziepe.ca, jrhilke@google.com, julianr@linux.ibm.com, kees@kernel.org, kevin.tian@intel.com, leon@kernel.org, leonro@nvidia.com, lukas@wunner.de, mattev@meta.com, michal.winiarski@intel.com, parav@nvidia.com, pasha.tatashin@soleen.com, praan@google.com, pratyush@kernel.org, rananta@google.com, rdunlap@infradead.org, rientjes@google.com, rodrigo.vivi@intel.com, rppt@kernel.org, saeedm@nvidia.com, schnelle@linux.ibm.com, skhan@linuxfoundation.org, vivek.kasireddy@intel.com, witu@nvidia.com, yanjun.zhu@linux.dev, yi.l.liu@intel.com Subject: Re: [PATCH v6 07/27] vfio/pci: Preserve vfio-pci device files across Live Update Message-ID: References: <20261102153656.1431701-1-vipinsh@google.com> <20261102153656.1431701-8-vipinsh@google.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20261102153656.1431701-8-vipinsh@google.com> On Mon, Nov 02, 2026 at 07:36:36AM -0800, Vipin Sharma wrote: >Implement the Live Update file handler callbacks to preserve a vfio-pci >device in noiommu mode across a Live Update while keeping it running >across kexec. Subsequent commits will enable userspace to retrieve and >take over this file after the Live Update. > >State about each device is serialized into struct vfio_pci_core_device_ser >using Kexec-Handover (KHO) to preserve the pages holding the struct and >the Live Update Orchestrator (LUO) to preserve the physical address of >the struct. > >Key design notes and constraints: > > * Noiommu-only policy and bound cdev requirement: can_preserve() verifies > that the preserved file is a bound vfio-pci cdev file descriptor via > vfio_file_is_bound_cdev(), and preserve() requires the device to be in > noiommu mode via vfio_device_is_noiommu() (returning -EOPNOTSUPP > otherwise). CONFIG_VFIO_PCI_LIVEUPDATE now depends on > CONFIG_VFIO_DEVICE_CDEV and CONFIG_VFIO_NOIOMMU. > > * Serialized state: During preserve(), serialize the PCI domain, BDF, > config space size, reset_works flag, and the initial pci_saved_state > captured when the device was first opened. During freeze(), snapshot > the virtualized PCI config space (vconfig) and capability map > (pci_config_map). > > * Keep-running freeze and unfreeze: Do not reset the device, clear > PCI_COMMAND_MASTER, zap BAR mappings, or revoke dma-bufs during > freeze(). Validate that VFIO interrupts are disabled, that the device > is in PCI_D0 (and not in VFIO runtime PM low-power mode), and that > SR-IOV is not enabled, as VFs are not preserved and the next kernel > disables SR-IOV on the running device. Then mask physical INTx > (recording the prior state) and mark the device frozen. If the > Live Update is aborted after freeze(), unfreeze() restores the physical > INTx state and clears liveupdate_frozen so the existing FD remains > usable. > > * TOCTOU synchronization: vfio_pci_dev_is_frozen() is checked locklessly > on entry to the ioctl, read/write and mmap paths, and re-checked under > a lock that freeze() holds before any operation that could change the > device or vconfig: under vdev->igate in vfio_pci_ioctl_set_irqs() and > around every config-space write in vfio_pci_config_rw_single(), under > vdev->memory_lock in vfio_pci_runtime_pm_entry(), > vfio_pci_ioctl_reset() and the SR-IOV enable path of > vfio_pci_core_sriov_configure(), and under dev_set->lock in > vfio_pci_dev_set_hot_reset(). A racing operation thus either completes > before freeze() takes its snapshot or fails, while existing BAR mmaps, > ioeventfds and dma-bufs keep working. Serializing config writes on > igate covers the PCI_COMMAND, INTx disable emulation, power state and > FLR paths at one point (the INTx disable emulation now uses the > igate-held __vfio_pci_intx_mask() and __vfio_pci_intx_unmask() > helpers), and also serializes the irq_type and virq_disabled accesses > of config writes with VFIO_DEVICE_SET_IRQS. > >Co-developed-by: David Matlack >Signed-off-by: David Matlack >Signed-off-by: Vipin Sharma >--- > drivers/vfio/pci/Kconfig | 2 +- > drivers/vfio/pci/vfio_pci_config.c | 19 +- > drivers/vfio/pci/vfio_pci_core.c | 49 +++- > drivers/vfio/pci/vfio_pci_intrs.c | 4 +- > drivers/vfio/pci/vfio_pci_liveupdate.c | 303 ++++++++++++++++++++++++- > drivers/vfio/pci/vfio_pci_priv.h | 13 ++ > include/linux/kho/abi/vfio_pci.h | 52 ++++- > include/linux/vfio_pci_core.h | 4 + > 8 files changed, 434 insertions(+), 12 deletions(-) > [snip] >diff --git a/include/linux/kho/abi/vfio_pci.h b/include/linux/kho/abi/vfio_pci.h >index 67e8199eec59..725043a44b55 100644 >--- a/include/linux/kho/abi/vfio_pci.h >+++ b/include/linux/kho/abi/vfio_pci.h >@@ -9,14 +9,19 @@ > #ifndef _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H > #define _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H > >+#include >+#include >+#include >+ > /** > * DOC: VFIO PCI Live Update ABI > * > * VFIO uses the ABI defined below for preserving device files across a kexec > * reboot using LUO. > * >- * Device metadata is serialized into memory which is then handed to the next >- * kernel via KHO. >+ * Device metadata, virtualized PCI configuration space, VFIO's capability map, >+ * and the initial PCI saved state captured when the device was first opened are >+ * serialized into memory which is then handed to the next kernel via KHO. > * > * This interface is a contract. Any modification to any of the serialization > * structs defined here constitutes a breaking change. Such changes require >@@ -25,4 +30,47 @@ > > #define VFIO_PCI_LUO_FH_COMPATIBLE "vfio-pci-v1" > >+/** >+ * define VFIO_PCI_SER_RESET_WORKS - Device supports function reset. >+ * >+ * Set in &vfio_pci_core_device_ser.flags when the preserved device had >+ * ``vdev->reset_works == true`` prior to kexec. >+ */ >+#define VFIO_PCI_SER_RESET_WORKS BIT(0) >+ >+#define VFIO_PCI_SER_KNOWN_FLAGS VFIO_PCI_SER_RESET_WORKS >+ >+/** >+ * struct vfio_pci_core_device_ser - Serialized state of a single VFIO PCI >+ * device. >+ * >+ * @domain: The device's PCI domain number (segment). >+ * @bdf: The device's PCI bus, device, and function number. >+ * @cfg_size: Size in bytes of the device's PCI configuration space >+ * (``PCI_CFG_SPACE_SIZE`` or ``PCI_CFG_SPACE_EXP_SIZE``). >+ * @size: Total size in bytes of this serialized buffer, equal to >+ * ``sizeof(struct vfio_pci_core_device_ser) + 2 * @cfg_size + @saved_state_size``. >+ * @flags: Bitmask of ``VFIO_PCI_SER_*`` flags; unknown bits are rejected. >+ * @saved_state_size: Size in bytes of the serialized &struct pci_saved_state_ser >+ * blob stored in @data after ``config_map``, or 0 if none. >+ * @reserved: Reserved for future use; must be 0. >+ * @data: Variable-length payload containing, in order: >+ * 1. ``u8 vconfig[@cfg_size]`` - VFIO virtualized config space snapshot >+ * captured during ``freeze()``. >+ * 2. ``u8 config_map[@cfg_size]`` - VFIO capability map snapshot >+ * captured during ``freeze()``. >+ * 3. ``u8 saved_state[@saved_state_size]`` - serialized >+ * &struct pci_saved_state_ser captured during ``preserve()``. >+ */ >+struct vfio_pci_core_device_ser { >+ u32 domain; >+ u16 bdf; >+ u16 cfg_size; >+ u32 size; >+ u32 flags; >+ u32 saved_state_size; We will need space for iommufd_token when we preserve that, we should probably add it now as otherwise the compatibility would be broken when we add it? Is the reserved here for that? >+ u32 reserved; >+ u8 data[]; >+} __packed; >+ > #endif /* _LINUX_LIVEUPDATE_ABI_VFIO_PCI_H */ >diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h >index 9a1674c152aa..6bae7581f4f4 100644 >--- a/include/linux/vfio_pci_core.h >+++ b/include/linux/vfio_pci_core.h >@@ -149,6 +149,10 @@ struct vfio_pci_core_device { > struct notifier_block nb; > struct rw_semaphore memory_lock; > struct list_head dmabufs; >+#ifdef CONFIG_VFIO_PCI_LIVEUPDATE >+ bool liveupdate_frozen; >+ bool liveupdate_intx_disabled; >+#endif > }; > > enum vfio_pci_io_width { >-- >2.56.0.317.g454f8302e1-goog > Thanks, Sami