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 --- kernel/bpf/arena.c | 77 ++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 71 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c index 1074ac4459f2..214a4da54162 100644 --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -7,6 +7,7 @@ #include #include #include +#include #include "range_tree.h" /* @@ -92,6 +93,62 @@ static long compute_pgoff(struct bpf_arena *arena, long uaddr) return (u32)(uaddr - (u32)arena->user_vm_start) >> PAGE_SHIFT; } +struct apply_range_data { + struct page **pages; + int i; +}; + +static int apply_range_set_cb(pte_t *pte, unsigned long addr, void *data) +{ + struct apply_range_data *d = data; + struct page *page; + + if (!data) + return 0; + /* sanity check */ + if (unlikely(!pte_none(ptep_get(pte)))) + return -EBUSY; + + page = d->pages[d->i++]; + /* paranoia, similar to vmap_pages_pte_range() */ + if (WARN_ON_ONCE(!pfn_valid(page_to_pfn(page)))) + return -EINVAL; + + set_pte_at(&init_mm, addr, pte, mk_pte(page, PAGE_KERNEL)); + return 0; +} + +static int apply_range_clear_cb(pte_t *pte, unsigned long addr, void *data) +{ + pte_t old_pte; + struct page *page; + + /* sanity check */ + old_pte = ptep_get(pte); + if (pte_none(old_pte) || !pte_present(old_pte)) + return 0; /* nothing to do */ + + /* get page and free it */ + page = pte_page(old_pte); + if (WARN_ON_ONCE(!page)) + return -EINVAL; + + pte_clear(&init_mm, addr, pte); + + /* ensure no stale TLB entries */ + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); + + __free_page(page); + + return 0; +} + +static int populate_pgtable_except_pte(struct bpf_arena *arena) +{ + return apply_to_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena), + KERN_VM_SZ - GUARD_SZ, apply_range_set_cb, NULL); +} + static struct bpf_map *arena_map_alloc(union bpf_attr *attr) { struct vm_struct *kern_vm; @@ -144,6 +201,12 @@ static struct bpf_map *arena_map_alloc(union bpf_attr *attr) goto err; } mutex_init(&arena->lock); + err = populate_pgtable_except_pte(arena); + if (err) { + range_tree_destroy(&arena->rt); + bpf_map_area_free(arena); + goto err; + } return &arena->map; err: @@ -286,6 +349,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf) if (ret) return VM_FAULT_SIGSEGV; + struct apply_range_data data = { .pages = &page, .i = 0 }; /* Account into memcg of the process that created bpf_arena */ ret = bpf_map_alloc_pages(map, NUMA_NO_NODE, 1, &page); if (ret) { @@ -293,7 +357,7 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf) return VM_FAULT_SIGSEGV; } - ret = vm_area_map_pages(arena->kern_vm, kaddr, kaddr + PAGE_SIZE, &page); + ret = apply_to_page_range(&init_mm, kaddr, PAGE_SIZE, apply_range_set_cb, &data); if (ret) { range_tree_set(&arena->rt, vmf->pgoff, 1); __free_page(page); @@ -428,7 +492,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt /* user_vm_end/start are fixed before bpf prog runs */ long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT; u64 kern_vm_start = bpf_arena_get_kern_vm_start(arena); - struct page **pages; + struct page **pages = NULL; long pgoff = 0; u32 uaddr32; int ret, i; @@ -465,6 +529,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt if (ret) goto out_free_pages; + struct apply_range_data data = { .pages = pages, .i = 0 }; ret = bpf_map_alloc_pages(&arena->map, node_id, page_cnt, pages); if (ret) goto out; @@ -477,8 +542,8 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt * kern_vm_start + uaddr32 + page_cnt * PAGE_SIZE - 1 can overflow * lower 32-bit and it's ok. */ - ret = vm_area_map_pages(arena->kern_vm, kern_vm_start + uaddr32, - kern_vm_start + uaddr32 + page_cnt * PAGE_SIZE, pages); + ret = apply_to_page_range(&init_mm, kern_vm_start + uaddr32, + page_cnt << PAGE_SHIFT, apply_range_set_cb, &data); if (ret) { for (i = 0; i < page_cnt; i++) __free_page(pages[i]); @@ -545,8 +610,8 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt) * page_cnt is big it's faster to do the batched zap. */ zap_pages(arena, full_uaddr, 1); - vm_area_unmap_pages(arena->kern_vm, kaddr, kaddr + PAGE_SIZE); - __free_page(page); + apply_to_existing_page_range(&init_mm, kaddr, PAGE_SIZE, apply_range_clear_cb, + NULL); } } -- 2.50.1