[PATCH bpf-next 04/16] bpf: Introduce bpf_arena.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

From: Alexei Starovoitov <ast@kernel.org>

Introduce bpf_arena, which is a sparse shared memory region between the bpf
program and user space.

Use cases:
1. User space mmap-s bpf_arena and uses it as a traditional mmap-ed anonymous
   region, like memcached or any key/value storage. The bpf program implements an
   in-kernel accelerator. XDP prog can search for a key in bpf_arena and return a
   value without going to user space.
2. The bpf program builds arbitrary data structures in bpf_arena (hash tables,
   rb-trees, sparse arrays), while user space occasionally consumes it.
3. bpf_arena is a "heap" of memory from the bpf program's point of view. It is
   not shared with user space.

Initially, the kernel vm_area and user vma are not populated. User space can
fault in pages within the range. While servicing a page fault, bpf_arena logic
will insert a new page into the kernel and user vmas. The bpf program can
allocate pages from that region via bpf_arena_alloc_pages(). This kernel
function will insert pages into the kernel vm_area. The subsequent fault-in
from user space will populate that page into the user vma. The
BPF_F_SEGV_ON_FAULT flag at arena creation time can be used to prevent fault-in
from user space. In such a case, if a page is not allocated by the bpf program
and not present in the kernel vm_area, the user process will segfault. This is
useful for use cases 2 and 3 above.

bpf_arena_alloc_pages() is similar to user space mmap(). It allocates pages
either at a specific address within the arena or allocates a range with the
maple tree. bpf_arena_free_pages() is analogous to munmap(), which frees pages
and removes the range from the kernel vm_area and from user process vmas.

bpf_arena can be used as a bpf program "heap" of up to 4GB. The memory is not
shared with user space. This is use case 3. In such a case, the
BPF_F_NO_USER_CONV flag is recommended. It will tell the verifier to treat the
rX = bpf_arena_cast_user(rY) instruction as a 32-bit move wX = wY, which will
improve bpf prog performance. Otherwise, bpf_arena_cast_user is translated by
JIT to conditionally add the upper 32 bits of user vm_start (if the pointer is
not NULL) to arena pointers before they are stored into memory. This way, user
space sees them as valid 64-bit pointers.

Diff https://github.com/llvm/llvm-project/pull/79902 taught LLVM BPF backend to
generate the bpf_cast_kern() instruction before dereference of the arena
pointer and the bpf_cast_user() instruction when the arena pointer is formed.
In a typical bpf program there will be very few bpf_cast_user().

From LLVM's point of view, arena pointers are tagged as
__attribute__((address_space(1))). Hence, clang provides helpful diagnostics
when pointers cross address space. Libbpf and the kernel support only
address_space == 1. All other address space identifiers are reserved.

rX = bpf_cast_kern(rY, addr_space) tells the verifier that
rX->type = PTR_TO_ARENA. Any further operations on PTR_TO_ARENA register have
to be in the 32-bit domain. The verifier will mark load/store through
PTR_TO_ARENA with PROBE_MEM32. JIT will generate them as
kern_vm_start + 32bit_addr memory accesses. The behavior is similar to
copy_from_kernel_nofault() except that no address checks are necessary. The
address is guaranteed to be in the 4GB range. If the page is not present, the
destination register is zeroed on read, and the operation is ignored on write.

rX = bpf_cast_user(rY, addr_space) tells the verifier that
rX->type = unknown scalar. If arena->map_flags has BPF_F_NO_USER_CONV set, then
the verifier converts cast_user to mov32. Otherwise, JIT will emit native code
equivalent to:
rX = (u32)rY;
if (rX)
  rX |= arena->user_vm_start & ~(u64)~0U;

After such conversion, the pointer becomes a valid user pointer within
bpf_arena range. The user process can access data structures created in
bpf_arena without any additional computations. For example, a linked list built
by a bpf program can be walked natively by user space.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 include/linux/bpf.h            |   5 +-
 include/linux/bpf_types.h      |   1 +
 include/uapi/linux/bpf.h       |   7 +
 kernel/bpf/Makefile            |   3 +
 kernel/bpf/arena.c             | 518 +++++++++++++++++++++++++++++++++
 kernel/bpf/core.c              |  11 +
 kernel/bpf/syscall.c           |   3 +
 kernel/bpf/verifier.c          |   1 +
 tools/include/uapi/linux/bpf.h |   7 +
 9 files changed, 554 insertions(+), 2 deletions(-)
 create mode 100644 kernel/bpf/arena.c

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1ebbee1d648e..42f22bc881f0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -37,6 +37,7 @@ struct perf_event;
 struct bpf_prog;
 struct bpf_prog_aux;
 struct bpf_map;
+struct bpf_arena;
 struct sock;
 struct seq_file;
 struct btf;
@@ -531,8 +532,8 @@ void bpf_list_head_free(const struct btf_field *field, void *list_head,
 			struct bpf_spin_lock *spin_lock);
 void bpf_rb_root_free(const struct btf_field *field, void *rb_root,
 		      struct bpf_spin_lock *spin_lock);
-
-
+u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena);
+u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena);
 int bpf_obj_name_cpy(char *dst, const char *src, unsigned int size);
 
 struct bpf_offload_dev;
diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 94baced5a1ad..9f2a6b83b49e 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -132,6 +132,7 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_STRUCT_OPS, bpf_struct_ops_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_RINGBUF, ringbuf_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_BLOOM_FILTER, bloom_filter_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_USER_RINGBUF, user_ringbuf_map_ops)
+BPF_MAP_TYPE(BPF_MAP_TYPE_ARENA, arena_map_ops)
 
 BPF_LINK_TYPE(BPF_LINK_TYPE_RAW_TRACEPOINT, raw_tracepoint)
 BPF_LINK_TYPE(BPF_LINK_TYPE_TRACING, tracing)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d96708380e52..f6648851eae6 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -983,6 +983,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_BLOOM_FILTER,
 	BPF_MAP_TYPE_USER_RINGBUF,
 	BPF_MAP_TYPE_CGRP_STORAGE,
+	BPF_MAP_TYPE_ARENA,
 	__MAX_BPF_MAP_TYPE
 };
 
@@ -1370,6 +1371,12 @@ enum {
 
 /* BPF token FD is passed in a corresponding command's token_fd field */
 	BPF_F_TOKEN_FD          = (1U << 16),
+
+/* When user space page faults in bpf_arena send SIGSEGV instead of inserting new page */
+	BPF_F_SEGV_ON_FAULT	= (1U << 17),
+
+/* Do not translate kernel bpf_arena pointers to user pointers */
+	BPF_F_NO_USER_CONV	= (1U << 18),
 };
 
 /* Flags for BPF_PROG_QUERY. */
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 4ce95acfcaa7..368c5d86b5b7 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -15,6 +15,9 @@ obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
 obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o
+ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)
+obj-$(CONFIG_BPF_SYSCALL) += arena.o
+endif
 obj-$(CONFIG_BPF_JIT) += dispatcher.o
 ifeq ($(CONFIG_NET),y)
 obj-$(CONFIG_BPF_SYSCALL) += devmap.o
diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
new file mode 100644
index 000000000000..9db720321700
--- /dev/null
+++ b/kernel/bpf/arena.c
@@ -0,0 +1,518 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/err.h>
+#include <linux/btf_ids.h>
+#include <linux/vmalloc.h>
+#include <linux/pagemap.h>
+
+/*
+ * bpf_arena is a sparsely populated shared memory region between bpf program and
+ * user space process.
+ *
+ * For example on x86-64 the values could be:
+ * user_vm_start 7f7d26200000     // picked by mmap()
+ * kern_vm_start ffffc90001e69000 // picked by get_vm_area()
+ * For user space all pointers within the arena are normal 8-byte addresses.
+ * In this example 7f7d26200000 is the address of the first page (pgoff=0).
+ * The bpf program will access it as: kern_vm_start + lower_32bit_of_user_ptr
+ * (u32)7f7d26200000 -> 26200000
+ * hence
+ * ffffc90001e69000 + 26200000 == ffffc90028069000 is "pgoff=0" within 4Gb
+ * kernel memory region.
+ *
+ * BPF JITs generate the following code to access arena:
+ *   mov eax, eax  // eax has lower 32-bit of user pointer
+ *   mov word ptr [rax + r12 + off], bx
+ * where r12 == kern_vm_start and off is s16.
+ * Hence allocate 4Gb + GUARD_SZ/2 on each side.
+ *
+ * Initially kernel vm_area and user vma are not populated.
+ * User space can fault-in any address which will insert the page
+ * into kernel and user vma.
+ * bpf program can allocate a page via bpf_arena_alloc_pages() kfunc
+ * which will insert it into kernel vm_area.
+ * The later fault-in from user space will populate that page into user vma.
+ */
+
+/* number of bytes addressable by LDX/STX insn with 16-bit 'off' field */
+#define GUARD_SZ (1ull << sizeof(((struct bpf_insn *)0)->off) * 8)
+#define KERN_VM_SZ ((1ull << 32) + GUARD_SZ)
+
+struct bpf_arena {
+	struct bpf_map map;
+	u64 user_vm_start;
+	u64 user_vm_end;
+	struct vm_struct *kern_vm;
+	struct maple_tree mt;
+	struct list_head vma_list;
+	struct mutex lock;
+};
+
+u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena)
+{
+	return arena ? (u64) (long) arena->kern_vm->addr + GUARD_SZ / 2 : 0;
+}
+
+u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena)
+{
+	return arena ? arena->user_vm_start : 0;
+}
+
+static long arena_map_peek_elem(struct bpf_map *map, void *value)
+{
+	return -EOPNOTSUPP;
+}
+
+static long arena_map_push_elem(struct bpf_map *map, void *value, u64 flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static long arena_map_pop_elem(struct bpf_map *map, void *value)
+{
+	return -EOPNOTSUPP;
+}
+
+static long arena_map_delete_elem(struct bpf_map *map, void *value)
+{
+	return -EOPNOTSUPP;
+}
+
+static int arena_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
+{
+	return -EOPNOTSUPP;
+}
+
+static long compute_pgoff(struct bpf_arena *arena, long uaddr)
+{
+	return (u32)(uaddr - (u32)arena->user_vm_start) >> PAGE_SHIFT;
+}
+
+#define MT_ENTRY ((void *)&arena_map_ops) /* unused. has to be valid pointer */
+
+/*
+ * Reserve a "zero page", so that bpf prog and user space never see
+ * a pointer to arena with lower 32 bits being zero.
+ * bpf_cast_user() promotes it to full 64-bit NULL.
+ */
+static int reserve_zero_page(struct bpf_arena *arena)
+{
+	long pgoff = compute_pgoff(arena, 0);
+
+	return mtree_insert(&arena->mt, pgoff, MT_ENTRY, GFP_KERNEL);
+}
+
+static struct bpf_map *arena_map_alloc(union bpf_attr *attr)
+{
+	struct vm_struct *kern_vm;
+	int numa_node = bpf_map_attr_numa_node(attr);
+	struct bpf_arena *arena;
+	int err = -ENOMEM;
+
+	if (attr->key_size != 8 || attr->value_size != 8 ||
+	    /* BPF_F_MMAPABLE must be set */
+	    !(attr->map_flags & BPF_F_MMAPABLE) ||
+	    /* No unsupported flags present */
+	    (attr->map_flags & ~(BPF_F_SEGV_ON_FAULT | BPF_F_MMAPABLE | BPF_F_NO_USER_CONV)))
+		return ERR_PTR(-EINVAL);
+
+	if (attr->map_extra & ~PAGE_MASK)
+		/* If non-zero the map_extra is an expected user VMA start address */
+		return ERR_PTR(-EINVAL);
+
+	kern_vm = get_vm_area(KERN_VM_SZ, VM_MAP | VM_USERMAP);
+	if (!kern_vm)
+		return ERR_PTR(-ENOMEM);
+
+	arena = bpf_map_area_alloc(sizeof(*arena), numa_node);
+	if (!arena)
+		goto err;
+
+	INIT_LIST_HEAD(&arena->vma_list);
+	arena->kern_vm = kern_vm;
+	arena->user_vm_start = attr->map_extra;
+	bpf_map_init_from_attr(&arena->map, attr);
+	mt_init_flags(&arena->mt, MT_FLAGS_ALLOC_RANGE);
+	mutex_init(&arena->lock);
+	if (arena->user_vm_start) {
+		err = reserve_zero_page(arena);
+		if (err) {
+			bpf_map_area_free(arena);
+			goto err;
+		}
+	}
+
+	return &arena->map;
+err:
+	free_vm_area(kern_vm);
+	return ERR_PTR(err);
+}
+
+static int for_each_pte(pte_t *ptep, unsigned long addr, void *data)
+{
+	struct page *page;
+	pte_t pte;
+
+	pte = ptep_get(ptep);
+	if (!pte_present(pte))
+		return 0;
+	page = pte_page(pte);
+	/*
+	 * We do not update pte here:
+	 * 1. Nobody should be accessing bpf_arena's range outside of a kernel bug
+	 * 2. TLB flushing is batched or deferred. Even if we clear pte,
+	 * the TLB entries can stick around and continue to permit access to
+	 * the freed page. So it all relies on 1.
+	 */
+	__free_page(page);
+	return 0;
+}
+
+static void arena_map_free(struct bpf_map *map)
+{
+	struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+
+	/*
+	 * Check that user vma-s are not around when bpf map is freed.
+	 * mmap() holds vm_file which holds bpf_map refcnt.
+	 * munmap() must have happened on vma followed by arena_vm_close()
+	 * which would clear arena->vma_list.
+	 */
+	if (WARN_ON_ONCE(!list_empty(&arena->vma_list)))
+		return;
+
+	/*
+	 * free_vm_area() calls remove_vm_area() that calls free_unmap_vmap_area().
+	 * It unmaps everything from vmalloc area and clears pgtables.
+	 * Call apply_to_existing_page_range() first to find populated ptes and
+	 * free those pages.
+	 */
+	apply_to_existing_page_range(&init_mm, bpf_arena_get_kern_vm_start(arena),
+				     KERN_VM_SZ - GUARD_SZ / 2, for_each_pte, NULL);
+	free_vm_area(arena->kern_vm);
+	mtree_destroy(&arena->mt);
+	bpf_map_area_free(arena);
+}
+
+static void *arena_map_lookup_elem(struct bpf_map *map, void *key)
+{
+	return ERR_PTR(-EINVAL);
+}
+
+static long arena_map_update_elem(struct bpf_map *map, void *key,
+				  void *value, u64 flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static int arena_map_check_btf(const struct bpf_map *map, const struct btf *btf,
+			       const struct btf_type *key_type, const struct btf_type *value_type)
+{
+	return 0;
+}
+
+static u64 arena_map_mem_usage(const struct bpf_map *map)
+{
+	return 0;
+}
+
+struct vma_list {
+	struct vm_area_struct *vma;
+	struct list_head head;
+};
+
+static int remember_vma(struct bpf_arena *arena, struct vm_area_struct *vma)
+{
+	struct vma_list *vml;
+
+	vml = kmalloc(sizeof(*vml), GFP_KERNEL);
+	if (!vml)
+		return -ENOMEM;
+	vma->vm_private_data = vml;
+	vml->vma = vma;
+	list_add(&vml->head, &arena->vma_list);
+	return 0;
+}
+
+static void arena_vm_close(struct vm_area_struct *vma)
+{
+	struct vma_list *vml;
+
+	vml = vma->vm_private_data;
+	list_del(&vml->head);
+	vma->vm_private_data = NULL;
+	kfree(vml);
+}
+
+static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
+{
+	struct bpf_map *map = vmf->vma->vm_file->private_data;
+	struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+	struct page *page;
+	long kbase, kaddr;
+	int ret;
+
+	kbase = bpf_arena_get_kern_vm_start(arena);
+	kaddr = kbase + (u32)(vmf->address & PAGE_MASK);
+
+	guard(mutex)(&arena->lock);
+	page = vmalloc_to_page((void *)kaddr);
+	if (page)
+		/* already have a page vmap-ed */
+		goto out;
+
+	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;
+
+	ret = mtree_insert(&arena->mt, vmf->pgoff, MT_ENTRY, GFP_KERNEL);
+	if (ret == -EEXIST)
+		return VM_FAULT_RETRY;
+	if (ret)
+		return VM_FAULT_SIGSEGV;
+
+	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
+	if (!page) {
+		mtree_erase(&arena->mt, vmf->pgoff);
+		return VM_FAULT_SIGSEGV;
+	}
+
+	ret = vmap_pages_range(kaddr, kaddr + PAGE_SIZE, PAGE_KERNEL, &page, PAGE_SHIFT);
+	if (ret) {
+		mtree_erase(&arena->mt, vmf->pgoff);
+		__free_page(page);
+		return VM_FAULT_SIGSEGV;
+	}
+out:
+	page_ref_add(page, 1);
+	vmf->page = page;
+	return 0;
+}
+
+static const struct vm_operations_struct arena_vm_ops = {
+	.close		= arena_vm_close,
+	.fault          = arena_vm_fault,
+};
+
+static int arena_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
+{
+	struct bpf_arena *arena = container_of(map, struct bpf_arena, map);
+	int err;
+
+	if (arena->user_vm_start && arena->user_vm_start != vma->vm_start)
+		/*
+		 * 1st user process can do mmap(NULL, ...) to pick user_vm_start
+		 * 2nd user process must pass the same addr to mmap(addr, MAP_FIXED..);
+		 *   or
+		 * specify addr in map_extra at map creation time and
+		 * use the same addr later with mmap(addr, MAP_FIXED..);
+		 */
+		return -EBUSY;
+
+	if (arena->user_vm_end && arena->user_vm_end != vma->vm_end)
+		/* all user processes must have the same size of mmap-ed region */
+		return -EBUSY;
+
+	if (vma->vm_end - vma->vm_start > 1ull << 32)
+		/* Must not be bigger than 4Gb */
+		return -E2BIG;
+
+	if (remember_vma(arena, vma))
+		return -ENOMEM;
+
+	if (!arena->user_vm_start) {
+		arena->user_vm_start = vma->vm_start;
+		err = reserve_zero_page(arena);
+		if (err)
+			return err;
+	}
+	arena->user_vm_end = vma->vm_end;
+	/*
+	 * bpf_map_mmap() checks that it's being mmaped as VM_SHARED and
+	 * clears VM_MAYEXEC. Set VM_DONTEXPAND as well to avoid
+	 * potential change of user_vm_start.
+	 */
+	vm_flags_set(vma, VM_DONTEXPAND);
+	vma->vm_ops = &arena_vm_ops;
+	return 0;
+}
+
+BTF_ID_LIST_SINGLE(bpf_arena_map_btf_ids, struct, bpf_arena)
+const struct bpf_map_ops arena_map_ops = {
+	.map_meta_equal = bpf_map_meta_equal,
+	.map_alloc = arena_map_alloc,
+	.map_free = arena_map_free,
+	.map_mmap = arena_map_mmap,
+	.map_get_next_key = arena_map_get_next_key,
+	.map_push_elem = arena_map_push_elem,
+	.map_peek_elem = arena_map_peek_elem,
+	.map_pop_elem = arena_map_pop_elem,
+	.map_lookup_elem = arena_map_lookup_elem,
+	.map_update_elem = arena_map_update_elem,
+	.map_delete_elem = arena_map_delete_elem,
+	.map_check_btf = arena_map_check_btf,
+	.map_mem_usage = arena_map_mem_usage,
+	.map_btf_id = &bpf_arena_map_btf_ids[0],
+};
+
+static u64 clear_lo32(u64 val)
+{
+	return val & ~(u64)~0U;
+}
+
+/*
+ * 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)
+{
+	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);
+	long pgoff = 0, kaddr, nr_pages = 0;
+	struct page **pages;
+	int ret, i;
+
+	if (page_cnt >= page_cnt_max)
+		return 0;
+
+	if (uaddr) {
+		if (uaddr & ~PAGE_MASK)
+			return 0;
+		pgoff = compute_pgoff(arena, uaddr);
+		if (pgoff + page_cnt > page_cnt_max)
+			/* requested address will be outside of user VMA */
+			return 0;
+	}
+
+	/* zeroing is needed, since alloc_pages_bulk_array() only fills in non-zero entries */
+	pages = kvcalloc(page_cnt, sizeof(struct page *), GFP_KERNEL);
+	if (!pages)
+		return 0;
+
+	guard(mutex)(&arena->lock);
+
+	if (uaddr)
+		ret = mtree_insert_range(&arena->mt, pgoff, pgoff + page_cnt,
+					 MT_ENTRY, GFP_KERNEL);
+	else
+		ret = mtree_alloc_range(&arena->mt, &pgoff, MT_ENTRY,
+					page_cnt, 0, page_cnt_max, GFP_KERNEL);
+	if (ret)
+		goto out_free_pages;
+
+	nr_pages = alloc_pages_bulk_array_node(GFP_KERNEL | __GFP_ZERO, node_id, page_cnt, pages);
+	if (nr_pages != page_cnt)
+		goto out;
+
+	kaddr = kern_vm_start + (u32)(arena->user_vm_start + pgoff * PAGE_SIZE);
+	ret = vmap_pages_range(kaddr, kaddr + PAGE_SIZE * page_cnt, PAGE_KERNEL,
+			       pages, PAGE_SHIFT);
+	if (ret)
+		goto out;
+	kvfree(pages);
+	return clear_lo32(arena->user_vm_start) + (u32)(kaddr - kern_vm_start);
+out:
+	mtree_erase(&arena->mt, pgoff);
+out_free_pages:
+	if (pages)
+		for (i = 0; i < nr_pages; i++)
+			__free_page(pages[i]);
+	kvfree(pages);
+	return 0;
+}
+
+/*
+ * If page is present in vmalloc area, unmap it from vmalloc area,
+ * unmap it from all user space vma-s,
+ * and free it.
+ */
+static void zap_pages(struct bpf_arena *arena, long uaddr, long page_cnt)
+{
+	struct vma_list *vml;
+
+	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)
+{
+	u64 full_uaddr, uaddr_end;
+	long kaddr, pgoff, i;
+	struct page *page;
+
+	/* only aligned lower 32-bit are relevant */
+	uaddr = (u32)uaddr;
+	uaddr &= PAGE_MASK;
+	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;
+
+	kaddr = bpf_arena_get_kern_vm_start(arena) + uaddr;
+
+	guard(mutex)(&arena->lock);
+
+	pgoff = compute_pgoff(arena, uaddr);
+	/* clear range */
+	mtree_store_range(&arena->mt, pgoff, pgoff + page_cnt, NULL, GFP_KERNEL);
+
+	if (page_cnt > 1)
+		/* bulk zap if multiple pages being freed */
+		zap_pages(arena, full_uaddr, page_cnt);
+
+	for (i = 0; i < page_cnt; i++, kaddr += PAGE_SIZE, full_uaddr += PAGE_SIZE) {
+		page = vmalloc_to_page((void *)kaddr);
+		if (!page)
+			continue;
+		if (page_cnt == 1 && page_mapped(page)) /* mapped by some user process */
+			zap_pages(arena, full_uaddr, 1);
+		vunmap_range(kaddr, kaddr + PAGE_SIZE);
+		__free_page(page);
+	}
+}
+
+__bpf_kfunc_start_defs();
+
+__bpf_kfunc void *bpf_arena_alloc_pages(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 || !arena->user_vm_start || flags)
+		return NULL;
+
+	return (void *)arena_alloc_pages(arena, (long)addr__ign, page_cnt, node_id);
+}
+
+__bpf_kfunc void bpf_arena_free_pages(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 || !arena->user_vm_start)
+		return;
+	arena_free_pages(arena, (long)ptr__ign, page_cnt);
+}
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(arena_kfuncs)
+BTF_ID_FLAGS(func, bpf_arena_alloc_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE)
+BTF_ID_FLAGS(func, bpf_arena_free_pages, KF_TRUSTED_ARGS | KF_SLEEPABLE)
+BTF_KFUNCS_END(arena_kfuncs)
+
+static const struct btf_kfunc_id_set common_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set   = &arena_kfuncs,
+};
+
+static int __init kfunc_init(void)
+{
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &common_kfunc_set);
+}
+late_initcall(kfunc_init);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 71c459a51d9e..2539d9bfe369 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2970,6 +2970,17 @@ void __weak arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp,
 {
 }
 
+/* for configs without MMU or 32-bit */
+__weak const struct bpf_map_ops arena_map_ops;
+__weak u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena)
+{
+	return 0;
+}
+__weak u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena)
+{
+	return 0;
+}
+
 #ifdef CONFIG_BPF_SYSCALL
 static int __init bpf_global_ma_init(void)
 {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b2750b79ac80..ac0e4a8bb852 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -164,6 +164,7 @@ static int bpf_map_update_value(struct bpf_map *map, struct file *map_file,
 	if (bpf_map_is_offloaded(map)) {
 		return bpf_map_offload_update_elem(map, key, value, flags);
 	} else if (map->map_type == BPF_MAP_TYPE_CPUMAP ||
+		   map->map_type == BPF_MAP_TYPE_ARENA ||
 		   map->map_type == BPF_MAP_TYPE_STRUCT_OPS) {
 		return map->ops->map_update_elem(map, key, value, flags);
 	} else if (map->map_type == BPF_MAP_TYPE_SOCKHASH ||
@@ -1160,6 +1161,7 @@ static int map_create(union bpf_attr *attr)
 	}
 
 	if (attr->map_type != BPF_MAP_TYPE_BLOOM_FILTER &&
+	    attr->map_type != BPF_MAP_TYPE_ARENA &&
 	    attr->map_extra != 0)
 		return -EINVAL;
 
@@ -1249,6 +1251,7 @@ static int map_create(union bpf_attr *attr)
 	case BPF_MAP_TYPE_LRU_PERCPU_HASH:
 	case BPF_MAP_TYPE_STRUCT_OPS:
 	case BPF_MAP_TYPE_CPUMAP:
+	case BPF_MAP_TYPE_ARENA:
 		if (!bpf_token_capable(token, CAP_BPF))
 			goto put_token;
 		break;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index db569ce89fb1..3c77a3ab1192 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -18047,6 +18047,7 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		case BPF_MAP_TYPE_SK_STORAGE:
 		case BPF_MAP_TYPE_TASK_STORAGE:
 		case BPF_MAP_TYPE_CGRP_STORAGE:
+		case BPF_MAP_TYPE_ARENA:
 			break;
 		default:
 			verbose(env,
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d96708380e52..f6648851eae6 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -983,6 +983,7 @@ enum bpf_map_type {
 	BPF_MAP_TYPE_BLOOM_FILTER,
 	BPF_MAP_TYPE_USER_RINGBUF,
 	BPF_MAP_TYPE_CGRP_STORAGE,
+	BPF_MAP_TYPE_ARENA,
 	__MAX_BPF_MAP_TYPE
 };
 
@@ -1370,6 +1371,12 @@ enum {
 
 /* BPF token FD is passed in a corresponding command's token_fd field */
 	BPF_F_TOKEN_FD          = (1U << 16),
+
+/* When user space page faults in bpf_arena send SIGSEGV instead of inserting new page */
+	BPF_F_SEGV_ON_FAULT	= (1U << 17),
+
+/* Do not translate kernel bpf_arena pointers to user pointers */
+	BPF_F_NO_USER_CONV	= (1U << 18),
 };
 
 /* Flags for BPF_PROG_QUERY. */
-- 
2.34.1