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Merge branch 'support-associating-bpf-programs-with-struct_ops'
Amery Hung says: ==================== Support associating BPF programs with struct_ops Hi, This patchset adds a new BPF command BPF_PROG_ASSOC_STRUCT_OPS to the bpf() syscall to allow associating a BPF program with a struct_ops. The command is introduced to address a emerging need from struct_ops users. As the number of subsystems adopting struct_ops grows, more users are building their struct_ops-based solution with some help from other BPF programs. For example, scx_layer uses a syscall program as a user space trigger to refresh layers [0]. It also uses tracing program to infer whether a task is using GPU and needs to be prioritized [1]. In these use cases, when there are multiple struct_ops instances, the struct_ops kfuncs called from different BPF programs, whether struct_ops or not needs to be able to refer to a specific one, which currently is not possible. The new BPF command will allow users to explicitly associate a BPF program with a struct_ops map. The libbpf wrapper can be called after loading programs and before attaching programs and struct_ops. Internally, it will set prog->aux->st_ops_assoc to the struct_ops map. struct_ops kfuncs can then get the associated struct_ops struct by calling bpf_prog_get_assoc_struct_ops() with prog->aux, which can be acquired from a "__prog" argument. The value of the special argument will be fixed up by the verifier during verification. The command conceptually associates the implementation of BPF programs with struct_ops map, not the attachment. A program associated with the map will take a refcount of it so that st_ops_assoc always points to a valid struct_ops struct. struct_ops implementers can use the helper, bpf_prog_get_assoc_struct_ops to get the pointer. The returned struct_ops if not NULL is guaranteed to be valid and initialized. However, it is not guaranteed that the struct_ops is attached. The struct_ops implementer still need to take steps to track and check the state of the struct_ops in kdata, if the use case demand the struct_ops to be attached. We can also consider support associating struct_ops link with BPF programs, which on one hand make struct_ops implementer's job easier, but might complicate libbpf workflow and does not apply to legacy struct_ops attachment. [0] https://github.com/sched-ext/scx/blob/main/scheds/rust/scx_layered/src/bpf/main.bpf.c#L557 [1] https://github.com/sched-ext/scx/blob/main/scheds/rust/scx_layered/src/bpf/main.bpf.c#L754 --- v7 -> v8 - Fix libbpf return (Andrii) - Follow kfunc _impl suffic naming convention in selftest (Alexei) Link: https://lore.kernel.org/bpf/20251121231352.4032020-1-ameryhung@gmail.com/ v6 -> v7 - Drop the guarantee that bpf_prog_get_assoc_struct_ops() will always return an initialized struct_ops (Martin) - Minor misc. changes in selftests Link: https://lore.kernel.org/bpf/20251114221741.317631-1-ameryhung@gmail.com/ v5 -> v6 - Drop refcnt bumping for async callbacks and add RCU annotation (Martin) - Fix libbpf bug and update comments (Andrii) - Fix refcount bug in bpf_prog_assoc_struct_ops() (AI) Link: https://lore.kernel.org/bpf/20251104172652.1746988-1-ameryhung@gmail.com/ v4 -> v5 - Simplify the API for getting associated struct_ops and dont't expose struct_ops map lifecycle management (Andrii, Alexei) Link: https://lore.kernel.org/bpf/20251024212914.1474337-1-ameryhung@gmail.com/ v3 -> v4 - Fix potential dangling pointer in timer callback. Protect st_ops_assoc with RCU. The get helper now needs to be paired with bpf_struct_ops_put() - The command should only increase refcount once for a program (Andrii) - Test a struct_ops program reused in two struct_ops maps - Test getting associated struct_ops in timer callback Link: https://lore.kernel.org/bpf/20251017215627.722338-1-ameryhung@gmail.com/ v2 -> v3 - Change the type of st_ops_assoc from void* (i.e., kdata) to bpf_map (Andrii) - Fix a bug that clears BPF_PTR_POISON when a struct_ops map is freed (Andrii) - Return NULL if the map is not fully initialized (Martin) - Move struct_ops map refcount inc/dec into internal helpers (Martin) - Add libbpf API, bpf_program__assoc_struct_ops (Andrii) Link: https://lore.kernel.org/bpf/20251016204503.3203690-1-ameryhung@gmail.com/ v1 -> v2 - Poison st_ops_assoc when reusing the program in more than one struct_ops maps and add a helper to access the pointer (Andrii) - Minor style and naming changes (Andrii) Link: https://lore.kernel.org/bpf/20251010174953.2884682-1-ameryhung@gmail.com/ --- ==================== Link: https://patch.msgid.link/20251203233748.668365-1-ameryhung@gmail.com Signed-off-by:Andrii Nakryiko <andrii@kernel.org>