From 27600805e62f800bacf990354632eae4e487d34c Mon Sep 17 00:00:00 2001 From: Yazen Ghannam Date: Thu, 3 Sep 2026 10:43:25 -0500 Subject: x86/amd_node: Fix PCI device reference counting in amd_smn_init() The local "root" pointer is a temporary variable used during the device search. Therefore, refcount related to the search iterators should be cleaned up after the search is complete. Use the __free() cleanup macro to ensure the refcount is decremented when the temporary pointer goes out of scope. Additionally, increment the refcount when caching a root pointer. This ensures the in-use refcount is separate from the temporary search refcounting. Finally, drop the redundant "root = NULL" before the second search loop. The pci_get_class() iterator always decrements the refcount of its "from" argument, so the first loop can only fall through with "root" already NULL. Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com Reported-by: Sashiko Assisted-by: LLM Signed-off-by: Yazen Ghannam Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Mario Limonciello (AMD) Cc: Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com --- Documentation/livepatch/system-state.rst | 167 +++++++++++++++++++++++++++++++ 1 file changed, 167 insertions(+) create mode 100644 Documentation/livepatch/system-state.rst (limited to 'Documentation/livepatch/system-state.rst') diff --git a/Documentation/livepatch/system-state.rst b/Documentation/livepatch/system-state.rst new file mode 100644 index 000000000..7a3935fd8 --- /dev/null +++ b/Documentation/livepatch/system-state.rst @@ -0,0 +1,167 @@ +==================== +System State Changes +==================== + +Some users are really reluctant to reboot a system. This brings the need +to provide more livepatches and maintain some compatibility between them. + +Maintaining more livepatches is much easier with cumulative livepatches. +Each new livepatch completely replaces any older one. It can keep, +add, and even remove fixes. And it is typically safe to replace any version +of the livepatch with any other one thanks to the atomic replace feature. + +The problems might come with shadow variables and callbacks. They might +change the system behavior or state so that it is no longer safe to +go back and use an older livepatch or the original kernel code. Also +any new livepatch must be able to detect what changes have already been +done by the already installed livepatches. + +This is where the livepatch system state tracking gets useful. It +allows to: + + - store data needed to manipulate and restore the system state + + - define compatibility between livepatches using a change id + and version + + +1. Livepatch system state API +============================= + +The state of the system might get modified either by several livepatch callbacks +or by the newly used code. Also it must be possible to find changes done by +already installed livepatches. + +Each modified state is described by struct klp_state, see +include/linux/livepatch.h. + +Each livepatch defines an array of struct klp_states. They mention +all states that the livepatch modifies. + +The livepatch author must define the following two fields for each +struct klp_state: + + - *id* + + - Non-zero number used to identify the affected system state. + + - *version* + + - Number describing the variant of the system state change that + is supported by the given livepatch. + +The state can be manipulated using two functions: + + - klp_get_state() + + - Get struct klp_state associated with the given livepatch + and state id. + + - klp_get_prev_state() + + - Get struct klp_state associated with the given feature id and + already installed livepatches. + +2. Livepatch compatibility +========================== + +The system state version is used to prevent loading incompatible livepatches. +The check is done when the livepatch is enabled. The rules are: + + - Any completely new system state modification is allowed. + + - System state modifications with the same or higher version are allowed + for already modified system states. + + - Cumulative livepatches must handle all system state modifications from + already installed livepatches. + + - Non-cumulative livepatches are allowed to touch already modified + system states. + +3. Supported scenarios +====================== + +Livepatches have their life-cycle and the same is true for the system +state changes. Every compatible livepatch has to support the following +scenarios: + + - Modify the system state when the livepatch gets enabled and the state + has not been already modified by a livepatches that are being + replaced. + + - Take over or update the system state modification when is has already + been done by a livepatch that is being replaced. + + - Restore the original state when the livepatch is disabled. + + - Restore the previous state when the transition is reverted. + It might be the original system state or the state modification + done by livepatches that were being replaced. + + - Remove any already made changes when error occurs and the livepatch + cannot get enabled. + +4. Expected usage +================= + +System states are usually modified by livepatch callbacks. The expected +role of each callback is as follows: + +*pre_patch()* + + - Allocate *state->data* when necessary. The allocation might fail + and *pre_patch()* is the only callback that could stop loading + of the livepatch. The allocation is not needed when the data + are already provided by previously installed livepatches. + + - Do any other preparatory action that is needed by + the new code even before the transition gets finished. + For example, initialize *state->data*. + + The system state itself is typically modified in *post_patch()* + when the entire system is able to handle it. + + - Clean up its own mess in case of error. It might be done by a custom + code or by calling *post_unpatch()* explicitly. + +*post_patch()* + + - Copy *state->data* from the previous livepatch when they are + compatible. + + - Do the actual system state modification. Eventually allow + the new code to use it. + + - Make sure that *state->data* has all necessary information. + + - Free *state->data* from replaces livepatches when they are + not longer needed. + +*pre_unpatch()* + + - Prevent the code, added by the livepatch, relying on the system + state change. + + - Revert the system state modification.. + +*post_unpatch()* + + - Distinguish transition reverse and livepatch disabling by + checking *klp_get_prev_state()*. + + - In case of transition reverse, restore the previous system + state. It might mean doing nothing. + + - Remove any not longer needed setting or data. + +.. note:: + + *pre_unpatch()* typically does symmetric operations to *post_patch()*. + Except that it is called only when the livepatch is being disabled. + Therefore it does not need to care about any previously installed + livepatch. + + *post_unpatch()* typically does symmetric operations to *pre_patch()*. + It might be called also during the transition reverse. Therefore it + has to handle the state of the previously installed livepatches. -- cgit v1.3.1