bpf: arena: allow calling from any context. #9997
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vm_area_map_pages() may allocate memory while inserting pages into bpf arena's vm_area. In order to make bpf_arena_alloc_pages() kfunc non-sleepable change bpf arena to populate pages without allocating memory: - at arena creation time populate all page table levels except the last level - when new pages need to be inserted call apply_to_page_range() again with apply_range_set_cb() which will only set_pte_at() those pages and will not allocate memory. - when freeing pages call apply_to_existing_page_range with apply_range_clear_cb() to clear the pte for the page to be removed. This doesn't free intermediate page table levels. Signed-off-by: Puranjay Mohan <[email protected]>
Make arena_free_pages() any context safe by deferring the main logic to a workqueue. This is done by calling irq_work_queue() which in turn calls schedule_work(). We can't directly call schedule_work() from arena_free_pages() as it is not safe. arena_free_pages() queues the address and the page count to be freed using a lock-less list of struct arena_free_spans. The arena_free_worker() (the work queue handler) iterates this list and handles the queued free requests. An instance of struct arena_free_span is allocated with kmalloc_nolock() in arena_free_pages(), but as kmalloc_nolock() can fail, a percpu pool of these structs is created at arena allocation time and this pool is used in case kmalloc_nolock() fails. The arena_free_worker() returns the spans back to the percpu pool of the cpu where they came from. Signed-off-by: Puranjay Mohan <[email protected]>
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vm_area_map_pages() may allocate memory while inserting pages into bpf arena's vm_area. In order to make bpf_arena_alloc_pages() kfunc non-sleepable change bpf arena to populate pages without allocating memory:
Co-developed-by: Alexei Starovoitov [email protected]