From cab056f2aae7250af50e503b81a80dfc567a1acd Mon Sep 17 00:00:00 2001 From: Pasha Tatashin Date: Thu, 18 Dec 2025 10:57:51 -0500 Subject: liveupdate: luo_flb: introduce File-Lifecycle-Bound global state Introduce a mechanism for managing global kernel state whose lifecycle is tied to the preservation of one or more files. This is necessary for subsystems where multiple preserved file descriptors depend on a single, shared underlying resource. An example is HugeTLB, where multiple file descriptors such as memfd and guest_memfd may rely on the state of a single HugeTLB subsystem. Preserving this state for each individual file would be redundant and incorrect. The state should be preserved only once when the first file is preserved, and restored/finished only once the last file is handled. This patch introduces File-Lifecycle-Bound (FLB) objects to solve this problem. An FLB is a global, reference-counted object with a defined set of operations: - A file handler (struct liveupdate_file_handler) declares a dependency on one or more FLBs via a new registration function, liveupdate_register_flb(). - When the first file depending on an FLB is preserved, the FLB's .preserve() callback is invoked to save the shared global state. The reference count is then incremented for each subsequent file. - Conversely, when the last file is unpreserved (before reboot) or finished (after reboot), the FLB's .unpreserve() or .finish() callback is invoked to clean up the global resource. The implementation includes: - A new set of ABI definitions (luo_flb_ser, luo_flb_head_ser) and a corresponding FDT node (luo-flb) to serialize the state of all active FLBs and pass them via Kexec Handover. - Core logic in luo_flb.c to manage FLB registration, reference counting, and the invocation of lifecycle callbacks. - An API (liveupdate_flb_get/_incoming/_outgoing) for other kernel subsystems to safely access the live object managed by an FLB, both before and after the live update. This framework provides the necessary infrastructure for more complex subsystems like IOMMU, VFIO, and KVM to integrate with the Live Update Orchestrator. Link: https://lkml.kernel.org/r/20251218155752.3045808-5-pasha.tatashin@soleen.com Signed-off-by: Pasha Tatashin Cc: Alexander Graf Cc: David Gow Cc: David Matlack Cc: David Rientjes Cc: Jonathan Corbet Cc: Kees Cook Cc: Mike Rapoport Cc: Petr Mladek Cc: Pratyush Yadav Cc: Samiullah Khawaja Cc: Tamir Duberstein Signed-off-by: Andrew Morton --- include/linux/liveupdate.h | 147 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 147 insertions(+) (limited to 'include/linux/liveupdate.h') diff --git a/include/linux/liveupdate.h b/include/linux/liveupdate.h index a7f6ee5b6771..fe82a6c3005f 100644 --- a/include/linux/liveupdate.h +++ b/include/linux/liveupdate.h @@ -11,10 +11,13 @@ #include #include #include +#include #include #include struct liveupdate_file_handler; +struct liveupdate_flb; +struct liveupdate_session; struct file; /** @@ -99,6 +102,118 @@ struct liveupdate_file_handler { * registered file handlers. */ struct list_head __private list; + /* A list of FLB dependencies. */ + struct list_head __private flb_list; +}; + +/** + * struct liveupdate_flb_op_args - Arguments for FLB operation callbacks. + * @flb: The global FLB instance for which this call is performed. + * @data: For .preserve(): [OUT] The callback sets this field. + * For .unpreserve(): [IN] The handle from .preserve(). + * For .retrieve(): [IN] The handle from .preserve(). + * @obj: For .preserve(): [OUT] Sets this to the live object. + * For .retrieve(): [OUT] Sets this to the live object. + * For .finish(): [IN] The live object from .retrieve(). + * + * This structure bundles all parameters for the FLB operation callbacks. + */ +struct liveupdate_flb_op_args { + struct liveupdate_flb *flb; + u64 data; + void *obj; +}; + +/** + * struct liveupdate_flb_ops - Callbacks for global File-Lifecycle-Bound data. + * @preserve: Called when the first file using this FLB is preserved. + * The callback must save its state and return a single, + * self-contained u64 handle by setting the 'argp->data' + * field and 'argp->obj'. + * @unpreserve: Called when the last file using this FLB is unpreserved + * (aborted before reboot). Receives the handle via + * 'argp->data' and live object via 'argp->obj'. + * @retrieve: Called on-demand in the new kernel, the first time a + * component requests access to the shared object. It receives + * the preserved handle via 'argp->data' and must reconstruct + * the live object, returning it by setting the 'argp->obj' + * field. + * @finish: Called in the new kernel when the last file using this FLB + * is finished. Receives the live object via 'argp->obj' for + * cleanup. + * @owner: Module reference + * + * Operations that manage global shared data with file bound lifecycle, + * triggered by the first file that uses it and concluded by the last file that + * uses it, across all sessions. + */ +struct liveupdate_flb_ops { + int (*preserve)(struct liveupdate_flb_op_args *argp); + void (*unpreserve)(struct liveupdate_flb_op_args *argp); + int (*retrieve)(struct liveupdate_flb_op_args *argp); + void (*finish)(struct liveupdate_flb_op_args *argp); + struct module *owner; +}; + +/* + * struct luo_flb_private_state - Private FLB state structures. + * @count: The number of preserved files currently depending on this FLB. + * This is used to trigger the preserve/unpreserve/finish ops on the + * first/last file. + * @data: The opaque u64 handle returned by .preserve() or passed to + * .retrieve(). + * @obj: The live kernel object returned by .preserve() or .retrieve(). + * @lock: A mutex that protects all fields within this structure, providing + * the synchronization service for the FLB's ops. + * @finished: True once the FLB's finish() callback has run. + * @retrieved: True once the FLB's retrieve() callback has run. + */ +struct luo_flb_private_state { + long count; + u64 data; + void *obj; + struct mutex lock; + bool finished; + bool retrieved; +}; + +/* + * struct luo_flb_private - Keep separate incoming and outgoing states. + * @list: A global list of registered FLBs. + * @outgoing: The runtime state for the pre-reboot + * (preserve/unpreserve) lifecycle. + * @incoming: The runtime state for the post-reboot (retrieve/finish) + * lifecycle. + * @users: With how many File-Handlers this FLB is registered. + * @initialized: true when private fields have been initialized. + */ +struct luo_flb_private { + struct list_head list; + struct luo_flb_private_state outgoing; + struct luo_flb_private_state incoming; + int users; + bool initialized; +}; + +/** + * struct liveupdate_flb - A global definition for a shared data object. + * @ops: Callback functions + * @compatible: The compatibility string (e.g., "iommu-core-v1" + * that uniquely identifies the FLB type this handler + * supports. This is matched against the compatible string + * associated with individual &struct liveupdate_flb + * instances. + * + * This struct is the "template" that a driver registers to define a shared, + * file-lifecycle-bound object. The actual runtime state (the live object, + * refcount, etc.) is managed privately by the LUO core. + */ +struct liveupdate_flb { + const struct liveupdate_flb_ops *ops; + const char compatible[LIVEUPDATE_FLB_COMPAT_LENGTH]; + + /* private: */ + struct luo_flb_private __private private; }; #ifdef CONFIG_LIVEUPDATE @@ -112,6 +227,14 @@ int liveupdate_reboot(void); int liveupdate_register_file_handler(struct liveupdate_file_handler *fh); int liveupdate_unregister_file_handler(struct liveupdate_file_handler *fh); +int liveupdate_register_flb(struct liveupdate_file_handler *fh, + struct liveupdate_flb *flb); +int liveupdate_unregister_flb(struct liveupdate_file_handler *fh, + struct liveupdate_flb *flb); + +int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, void **objp); +int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, void **objp); + #else /* CONFIG_LIVEUPDATE */ static inline bool liveupdate_enabled(void) @@ -134,5 +257,29 @@ static inline int liveupdate_unregister_file_handler(struct liveupdate_file_hand return -EOPNOTSUPP; } +static inline int liveupdate_register_flb(struct liveupdate_file_handler *fh, + struct liveupdate_flb *flb) +{ + return -EOPNOTSUPP; +} + +static inline int liveupdate_unregister_flb(struct liveupdate_file_handler *fh, + struct liveupdate_flb *flb) +{ + return -EOPNOTSUPP; +} + +static inline int liveupdate_flb_get_incoming(struct liveupdate_flb *flb, + void **objp) +{ + return -EOPNOTSUPP; +} + +static inline int liveupdate_flb_get_outgoing(struct liveupdate_flb *flb, + void **objp) +{ + return -EOPNOTSUPP; +} + #endif /* CONFIG_LIVEUPDATE */ #endif /* _LINUX_LIVEUPDATE_H */ -- cgit v1.2.3