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bpf: arena: make arena kfuncs any context safe

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Make arena related kfuncs any context safe by the following changes:

bpf_arena_alloc_pages() and bpf_arena_reserve_pages():
Replace the usage of the mutex with a rqspinlock for range tree and use
kmalloc_nolock() wherever needed. Use free_pages_nolock() to free pages
from any context.
apply_range_set/clear_cb() with apply_to_page_range() has already made
populating the vm_area in bpf_arena_alloc_pages() any context safe.

bpf_arena_free_pages(): defer the main logic to a workqueue if it is
called from a non-sleepable context.

specialize_kfunc() is used to replace the sleepable arena_free_pages()
with bpf_arena_free_pages_non_sleepable() when the verifier detects the
call is from a non-sleepable context.

In the non-sleepable case, arena_free_pages() queues the address and the
page count to be freed to a lock-less list of struct arena_free_spans
and raises an irq_work. The irq_work handler calls schedules_work() as
it is safe to be called from irq context.  arena_free_worker() (the work
queue handler) iterates these spans and clears ptes, flushes tlb, zaps
pages, and calls __free_page().

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20251222195022.431211-4-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Puranjay Mohan 2025-12-22 11:50:18 -08:00 committed by Alexei Starovoitov
parent 360c35f8ff
commit b8467290ed
3 changed files with 234 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
include/linux/bpf.h
View File

@ -673,6 +673,22 @@ void bpf_map_free_internal_structs(struct bpf_map *map, void *obj);
int bpf_dynptr_from_file_sleepable(struct file *file, u32 flags,
struct bpf_dynptr *ptr__uninit);
#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
void *bpf_arena_alloc_pages_non_sleepable(void *p__map, void *addr__ign, u32 page_cnt, int node_id,
u64 flags);
void bpf_arena_free_pages_non_sleepable(void *p__map, void *ptr__ign, u32 page_cnt);
#else
static inline void *bpf_arena_alloc_pages_non_sleepable(void *p__map, void *addr__ign, u32 page_cnt,
int node_id, u64 flags)
{
return NULL;
}
static inline void bpf_arena_free_pages_non_sleepable(void *p__map, void *ptr__ign, u32 page_cnt)
{
}
#endif
extern const struct bpf_map_ops bpf_map_offload_ops;
/* bpf_type_flag contains a set of flags that are applicable to the values of

250
kernel/bpf/arena.c
View File

@ -4,7 +4,9 @@
#include <linux/btf.h>
#include <linux/cacheflush.h>
#include <linux/err.h>
#include <linux/irq_work.h>
#include "linux/filter.h"
#include <linux/llist.h>
#include <linux/btf_ids.h>
#include <linux/vmalloc.h>
#include <linux/pagemap.h>
@ -44,7 +46,7 @@
#define GUARD_SZ round_up(1ull << sizeof_field(struct bpf_insn, off) * 8, PAGE_SIZE << 1)
#define KERN_VM_SZ (SZ_4G + GUARD_SZ)
static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt);
static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt, bool sleepable);
struct bpf_arena {
struct bpf_map map;
@ -52,8 +54,23 @@ struct bpf_arena {
u64 user_vm_end;
struct vm_struct *kern_vm;
struct range_tree rt;
/* protects rt */
rqspinlock_t spinlock;
struct list_head vma_list;
/* protects vma_list */
struct mutex lock;
struct irq_work free_irq;
struct work_struct free_work;
struct llist_head free_spans;
};
static void arena_free_worker(struct work_struct *work);
static void arena_free_irq(struct irq_work *iw);
struct arena_free_span {
struct llist_node node;
unsigned long uaddr;
u32 page_cnt;
};
u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena)
@ -127,7 +144,7 @@ static void flush_vmap_cache(unsigned long start, unsigned long size)
flush_cache_vmap(start, start + size);
}
static int apply_range_clear_cb(pte_t *pte, unsigned long addr, void *data)
static int apply_range_clear_cb(pte_t *pte, unsigned long addr, void *free_pages)
{
pte_t old_pte;
struct page *page;
@ -137,17 +154,15 @@ static int apply_range_clear_cb(pte_t *pte, unsigned long addr, void *data)
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);
/* Add page to the list so it is freed later */
if (free_pages)
__llist_add(&page->pcp_llist, free_pages);
return 0;
}
@ -202,6 +217,9 @@ static struct bpf_map *arena_map_alloc(union bpf_attr *attr)
arena->user_vm_end = arena->user_vm_start + vm_range;
INIT_LIST_HEAD(&arena->vma_list);
init_llist_head(&arena->free_spans);
init_irq_work(&arena->free_irq, arena_free_irq);
INIT_WORK(&arena->free_work, arena_free_worker);
bpf_map_init_from_attr(&arena->map, attr);
range_tree_init(&arena->rt);
err = range_tree_set(&arena->rt, 0, attr->max_entries);
@ -210,6 +228,7 @@ static struct bpf_map *arena_map_alloc(union bpf_attr *attr)
goto err;
}
mutex_init(&arena->lock);
raw_res_spin_lock_init(&arena->spinlock);
err = populate_pgtable_except_pte(arena);
if (err) {
range_tree_destroy(&arena->rt);
@ -256,6 +275,10 @@ static void arena_map_free(struct bpf_map *map)
if (WARN_ON_ONCE(!list_empty(&arena->vma_list)))
return;
/* Ensure no pending deferred frees */
irq_work_sync(&arena->free_irq);
flush_work(&arena->free_work);
/*
* free_vm_area() calls remove_vm_area() that calls free_unmap_vmap_area().
* It unmaps everything from vmalloc area and clears pgtables.
@ -339,12 +362,16 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
struct page *page;
long kbase, kaddr;
unsigned long flags;
int ret;
kbase = bpf_arena_get_kern_vm_start(arena);
kaddr = kbase + (u32)(vmf->address);
guard(mutex)(&arena->lock);
if (raw_res_spin_lock_irqsave(&arena->spinlock, flags))
/* Make a reasonable effort to address impossible case */
return VM_FAULT_RETRY;
page = vmalloc_to_page((void *)kaddr);
if (page)
/* already have a page vmap-ed */
@ -352,31 +379,35 @@ static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
if (arena->map.map_flags & BPF_F_SEGV_ON_FAULT)
/* User space requested to segfault when page is not allocated by bpf prog */
return VM_FAULT_SIGSEGV;
goto out_unlock_sigsegv;
ret = range_tree_clear(&arena->rt, vmf->pgoff, 1);
if (ret)
return VM_FAULT_SIGSEGV;
goto out_unlock_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) {
range_tree_set(&arena->rt, vmf->pgoff, 1);
return VM_FAULT_SIGSEGV;
goto out_unlock_sigsegv;
}
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);
return VM_FAULT_SIGSEGV;
free_pages_nolock(page, 0);
goto out_unlock_sigsegv;
}
flush_vmap_cache(kaddr, PAGE_SIZE);
out:
page_ref_add(page, 1);
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
vmf->page = page;
return 0;
out_unlock_sigsegv:
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
return VM_FAULT_SIGSEGV;
}
static const struct vm_operations_struct arena_vm_ops = {
@ -497,7 +528,8 @@ static u64 clear_lo32(u64 val)
* Allocate pages and vmap them into kernel vmalloc area.
* Later the pages will be mmaped into user space vma.
*/
static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt, int node_id)
static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt, int node_id,
bool sleepable)
{
/* user_vm_end/start are fixed before bpf prog runs */
long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT;
@ -506,6 +538,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
struct page **pages = NULL;
long remaining, mapped = 0;
long alloc_pages;
unsigned long flags;
long pgoff = 0;
u32 uaddr32;
int ret, i;
@ -529,7 +562,8 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
return 0;
data.pages = pages;
mutex_lock(&arena->lock);
if (raw_res_spin_lock_irqsave(&arena->spinlock, flags))
goto out_free_pages;
if (uaddr) {
ret = is_range_tree_set(&arena->rt, pgoff, page_cnt);
@ -573,7 +607,7 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
/* data.i pages were mapped, account them and free the remaining */
mapped += data.i;
for (i = data.i; i < this_batch; i++)
__free_page(pages[i]);
free_pages_nolock(pages[i], 0);
goto out;
}
@ -581,19 +615,19 @@ static long arena_alloc_pages(struct bpf_arena *arena, long uaddr, long page_cnt
remaining -= this_batch;
}
flush_vmap_cache(kern_vm_start + uaddr32, mapped << PAGE_SHIFT);
mutex_unlock(&arena->lock);
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
kfree_nolock(pages);
return clear_lo32(arena->user_vm_start) + uaddr32;
out:
range_tree_set(&arena->rt, pgoff + mapped, page_cnt - mapped);
mutex_unlock(&arena->lock);
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
if (mapped) {
flush_vmap_cache(kern_vm_start + uaddr32, mapped << PAGE_SHIFT);
arena_free_pages(arena, uaddr32, mapped);
arena_free_pages(arena, uaddr32, mapped, sleepable);
}
goto out_free_pages;
out_unlock_free_pages:
mutex_unlock(&arena->lock);
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
out_free_pages:
kfree_nolock(pages);
return 0;
@ -608,42 +642,64 @@ static void zap_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
{
struct vma_list *vml;
guard(mutex)(&arena->lock);
/* iterate link list under lock */
list_for_each_entry(vml, &arena->vma_list, head)
zap_page_range_single(vml->vma, uaddr,
PAGE_SIZE * page_cnt, NULL);
}
static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt, bool sleepable)
{
u64 full_uaddr, uaddr_end;
long kaddr, pgoff, i;
long kaddr, pgoff;
struct page *page;
struct llist_head free_pages;
struct llist_node *pos, *t;
struct arena_free_span *s;
unsigned long flags;
int ret = 0;
/* only aligned lower 32-bit are relevant */
uaddr = (u32)uaddr;
uaddr &= PAGE_MASK;
kaddr = bpf_arena_get_kern_vm_start(arena) + uaddr;
full_uaddr = clear_lo32(arena->user_vm_start) + uaddr;
uaddr_end = min(arena->user_vm_end, full_uaddr + (page_cnt << PAGE_SHIFT));
if (full_uaddr >= uaddr_end)
return;
page_cnt = (uaddr_end - full_uaddr) >> PAGE_SHIFT;
guard(mutex)(&arena->lock);
pgoff = compute_pgoff(arena, uaddr);
/* clear range */
if (!sleepable)
goto defer;
ret = raw_res_spin_lock_irqsave(&arena->spinlock, flags);
/* Can't proceed without holding the spinlock so defer the free */
if (ret)
goto defer;
range_tree_set(&arena->rt, pgoff, page_cnt);
init_llist_head(&free_pages);
/* clear ptes and collect struct pages */
apply_to_existing_page_range(&init_mm, kaddr, page_cnt << PAGE_SHIFT,
apply_range_clear_cb, &free_pages);
/* drop the lock to do the tlb flush and zap pages */
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
/* ensure no stale TLB entries */
flush_tlb_kernel_range(kaddr, kaddr + (page_cnt * PAGE_SIZE));
if (page_cnt > 1)
/* bulk zap if multiple pages being freed */
zap_pages(arena, full_uaddr, page_cnt);
kaddr = bpf_arena_get_kern_vm_start(arena) + uaddr;
for (i = 0; i < page_cnt; i++, kaddr += PAGE_SIZE, full_uaddr += PAGE_SIZE) {
page = vmalloc_to_page((void *)kaddr);
if (!page)
continue;
llist_for_each_safe(pos, t, __llist_del_all(&free_pages)) {
page = llist_entry(pos, struct page, pcp_llist);
if (page_cnt == 1 && page_mapped(page)) /* mapped by some user process */
/* Optimization for the common case of page_cnt==1:
* If page wasn't mapped into some user vma there
@ -651,9 +707,25 @@ 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);
apply_to_existing_page_range(&init_mm, kaddr, PAGE_SIZE, apply_range_clear_cb,
NULL);
__free_page(page);
}
return;
defer:
s = kmalloc_nolock(sizeof(struct arena_free_span), 0, -1);
if (!s)
/*
* If allocation fails in non-sleepable context, pages are intentionally left
* inaccessible (leaked) until the arena is destroyed. Cleanup or retries are not
* possible here, so we intentionally omit them for safety.
*/
return;
s->page_cnt = page_cnt;
s->uaddr = uaddr;
llist_add(&s->node, &arena->free_spans);
irq_work_queue(&arena->free_irq);
}
/*
@ -663,6 +735,7 @@ static void arena_free_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
static int arena_reserve_pages(struct bpf_arena *arena, long uaddr, u32 page_cnt)
{
long page_cnt_max = (arena->user_vm_end - arena->user_vm_start) >> PAGE_SHIFT;
unsigned long flags;
long pgoff;
int ret;
@ -673,15 +746,87 @@ static int arena_reserve_pages(struct bpf_arena *arena, long uaddr, u32 page_cnt
if (pgoff + page_cnt > page_cnt_max)
return -EINVAL;
guard(mutex)(&arena->lock);
if (raw_res_spin_lock_irqsave(&arena->spinlock, flags))
return -EBUSY;
/* Cannot guard already allocated pages. */
ret = is_range_tree_set(&arena->rt, pgoff, page_cnt);
if (ret)
return -EBUSY;
if (ret) {
ret = -EBUSY;
goto out;
}
/* "Allocate" the region to prevent it from being allocated. */
return range_tree_clear(&arena->rt, pgoff, page_cnt);
ret = range_tree_clear(&arena->rt, pgoff, page_cnt);
out:
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
return ret;
}
static void arena_free_worker(struct work_struct *work)
{
struct bpf_arena *arena = container_of(work, struct bpf_arena, free_work);
struct llist_node *list, *pos, *t;
struct arena_free_span *s;
u64 arena_vm_start, user_vm_start;
struct llist_head free_pages;
struct page *page;
unsigned long full_uaddr;
long kaddr, page_cnt, pgoff;
unsigned long flags;
if (raw_res_spin_lock_irqsave(&arena->spinlock, flags)) {
schedule_work(work);
return;
}
init_llist_head(&free_pages);
arena_vm_start = bpf_arena_get_kern_vm_start(arena);
user_vm_start = bpf_arena_get_user_vm_start(arena);
list = llist_del_all(&arena->free_spans);
llist_for_each(pos, list) {
s = llist_entry(pos, struct arena_free_span, node);
page_cnt = s->page_cnt;
kaddr = arena_vm_start + s->uaddr;
pgoff = compute_pgoff(arena, s->uaddr);
/* clear ptes and collect pages in free_pages llist */
apply_to_existing_page_range(&init_mm, kaddr, page_cnt << PAGE_SHIFT,
apply_range_clear_cb, &free_pages);
range_tree_set(&arena->rt, pgoff, page_cnt);
}
raw_res_spin_unlock_irqrestore(&arena->spinlock, flags);
/* Iterate the list again without holding spinlock to do the tlb flush and zap_pages */
llist_for_each_safe(pos, t, list) {
s = llist_entry(pos, struct arena_free_span, node);
page_cnt = s->page_cnt;
full_uaddr = clear_lo32(user_vm_start) + s->uaddr;
kaddr = arena_vm_start + s->uaddr;
/* ensure no stale TLB entries */
flush_tlb_kernel_range(kaddr, kaddr + (page_cnt * PAGE_SIZE));
/* remove pages from user vmas */
zap_pages(arena, full_uaddr, page_cnt);
kfree_nolock(s);
}
/* free all pages collected by apply_to_existing_page_range() in the first loop */
llist_for_each_safe(pos, t, __llist_del_all(&free_pages)) {
page = llist_entry(pos, struct page, pcp_llist);
__free_page(page);
}
}
static void arena_free_irq(struct irq_work *iw)
{
struct bpf_arena *arena = container_of(iw, struct bpf_arena, free_irq);
schedule_work(&arena->free_work);
}
__bpf_kfunc_start_defs();
@ -695,9 +840,20 @@ __bpf_kfunc void *bpf_arena_alloc_pages(void *p__map, void *addr__ign, u32 page_
if (map->map_type != BPF_MAP_TYPE_ARENA || flags || !page_cnt)
return NULL;
return (void *)arena_alloc_pages(arena, (long)addr__ign, page_cnt, node_id);
return (void *)arena_alloc_pages(arena, (long)addr__ign, page_cnt, node_id, true);
}
void *bpf_arena_alloc_pages_non_sleepable(void *p__map, void *addr__ign, u32 page_cnt,
int node_id, u64 flags)
{
struct bpf_map *map = p__map;
struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
if (map->map_type != BPF_MAP_TYPE_ARENA || flags || !page_cnt)
return NULL;
return (void *)arena_alloc_pages(arena, (long)addr__ign, page_cnt, node_id, false);
}
__bpf_kfunc void bpf_arena_free_pages(void *p__map, void *ptr__ign, u32 page_cnt)
{
struct bpf_map *map = p__map;
@ -705,7 +861,17 @@ __bpf_kfunc void bpf_arena_free_pages(void *p__map, void *ptr__ign, u32 page_cnt
if (map->map_type != BPF_MAP_TYPE_ARENA || !page_cnt || !ptr__ign)
return;
arena_free_pages(arena, (long)ptr__ign, page_cnt);
arena_free_pages(arena, (long)ptr__ign, page_cnt, true);
}
void bpf_arena_free_pages_non_sleepable(void *p__map, void *ptr__ign, u32 page_cnt)
{
struct bpf_map *map = p__map;
struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
if (map->map_type != BPF_MAP_TYPE_ARENA || !page_cnt || !ptr__ign)
return;
arena_free_pages(arena, (long)ptr__ign, page_cnt, false);
}
__bpf_kfunc int bpf_arena_reserve_pages(void *p__map, void *ptr__ign, u32 page_cnt)
@ -724,9 +890,9 @@ __bpf_kfunc int bpf_arena_reserve_pages(void *p__map, void *ptr__ign, u32 page_c
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(arena_kfuncs)
BTF_ID_FLAGS(func, bpf_arena_alloc_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_RET | KF_ARENA_ARG2)
BTF_ID_FLAGS(func, bpf_arena_free_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_ARG2)
BTF_ID_FLAGS(func, bpf_arena_reserve_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE | KF_ARENA_ARG2)
BTF_ID_FLAGS(func, bpf_arena_alloc_pages, KF_TRUSTED_ARGS | KF_ARENA_RET | KF_ARENA_ARG2)
BTF_ID_FLAGS(func, bpf_arena_free_pages, KF_TRUSTED_ARGS | KF_ARENA_ARG2)
BTF_ID_FLAGS(func, bpf_arena_reserve_pages, KF_TRUSTED_ARGS | KF_ARENA_ARG2)
BTF_KFUNCS_END(arena_kfuncs)
static const struct btf_kfunc_id_set common_kfunc_set = {

10
kernel/bpf/verifier.c
View File

@ -12380,6 +12380,8 @@ enum special_kfunc_type {
KF___bpf_trap,
KF_bpf_task_work_schedule_signal_impl,
KF_bpf_task_work_schedule_resume_impl,
KF_bpf_arena_alloc_pages,
KF_bpf_arena_free_pages,
};
BTF_ID_LIST(special_kfunc_list)
@ -12454,6 +12456,8 @@ BTF_ID(func, bpf_dynptr_file_discard)
BTF_ID(func, __bpf_trap)
BTF_ID(func, bpf_task_work_schedule_signal_impl)
BTF_ID(func, bpf_task_work_schedule_resume_impl)
BTF_ID(func, bpf_arena_alloc_pages)
BTF_ID(func, bpf_arena_free_pages)
static bool is_task_work_add_kfunc(u32 func_id)
{
@ -22432,6 +22436,12 @@ static int specialize_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_desc
} else if (func_id == special_kfunc_list[KF_bpf_dynptr_from_file]) {
if (!env->insn_aux_data[insn_idx].non_sleepable)
addr = (unsigned long)bpf_dynptr_from_file_sleepable;
} else if (func_id == special_kfunc_list[KF_bpf_arena_alloc_pages]) {
if (env->insn_aux_data[insn_idx].non_sleepable)
addr = (unsigned long)bpf_arena_alloc_pages_non_sleepable;
} else if (func_id == special_kfunc_list[KF_bpf_arena_free_pages]) {
if (env->insn_aux_data[insn_idx].non_sleepable)
addr = (unsigned long)bpf_arena_free_pages_non_sleepable;
}
desc->addr = addr;
return 0;