[PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps

[PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps

[Andrii Nakryiko]

This patch set adds ability to memory-map BPF array maps (single- and
multi-element). The primary use case is memory-mapping BPF array maps, created
to back global data variables, created by libbpf implicitly. This allows for
much better usability, along with avoiding syscalls to read or update data
completely.

Due to memory-mapping requirements, BPF array map that is supposed to be
memory-mapped, has to be created with special BPF_F_MMAPABLE attribute, which
triggers slightly different memory allocation strategy internally. See
patch 1 for details.

Libbpf is extended to detect kernel support for this flag, and if supported,
will specify it for all global data maps automatically.

Andrii Nakryiko (3):
  bpf: add mmap() support for BPF_MAP_TYPE_ARRAY
  libbpf: make global data internal arrays mmap()-able, if possible
  selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests

 include/linux/bpf.h                           |   8 +-
 include/uapi/linux/bpf.h                      |   3 +
 kernel/bpf/arraymap.c                         |  96 ++++++++++-
 kernel/bpf/syscall.c                          |  39 +++++
 tools/include/uapi/linux/bpf.h                |   3 +
 tools/lib/bpf/libbpf.c                        |  31 +++-
 .../selftests/bpf/prog_tests/core_reloc.c     |  45 +++--
 tools/testing/selftests/bpf/prog_tests/mmap.c | 154 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_mmap.c |  31 ++++
 9 files changed, 380 insertions(+), 30 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/mmap.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_mmap.c

-- 
2.17.1

[PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY

[Andrii Nakryiko]

Add ability to memory-map contents of BPF array map. This is extremely useful
for working with BPF global data from userspace programs. It allows to avoid
typical bpf_map_{lookup,update}_elem operations, improving both performance
and usability.

There had to be special considerations for map freezing, to avoid having
writable memory view into a frozen map. To solve this issue, map freezing and
mmap-ing is happening under mutex now:
  - if map is already frozen, no writable mapping is allowed;
  - if map has writable memory mappings active (accounted in map->writecnt),
    map freezing will keep failing with -EBUSY;
  - once number of writable memory mappings drops to zero, map freezing can be
    performed again.

Only non-per-CPU arrays are supported right now. Maps with spinlocks can't be
memory mapped either.

Cc: Rik van Riel <riel@surriel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 include/linux/bpf.h            |  8 ++-
 include/uapi/linux/bpf.h       |  3 ++
 kernel/bpf/arraymap.c          | 96 +++++++++++++++++++++++++++++++---
 kernel/bpf/syscall.c           | 39 ++++++++++++++
 tools/include/uapi/linux/bpf.h |  3 ++
 5 files changed, 139 insertions(+), 10 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 7c7f518811a6..489014097657 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -12,6 +12,7 @@
 #include <linux/err.h>
 #include <linux/rbtree_latch.h>
 #include <linux/numa.h>
+#include <linux/mm_types.h>
 #include <linux/wait.h>
 #include <linux/u64_stats_sync.h>
 
@@ -66,6 +67,7 @@ struct bpf_map_ops {
 				     u64 *imm, u32 off);
 	int (*map_direct_value_meta)(const struct bpf_map *map,
 				     u64 imm, u32 *off);
+	int (*map_mmap)(struct bpf_map *map, struct vm_area_struct *vma);
 };
 
 struct bpf_map_memory {
@@ -95,7 +97,7 @@ struct bpf_map {
 	struct btf *btf;
 	struct bpf_map_memory memory;
 	bool unpriv_array;
-	bool frozen; /* write-once */
+	bool frozen; /* write-once; write-protected by freeze_mutex */
 	/* 48 bytes hole */
 
 	/* The 3rd and 4th cacheline with misc members to avoid false sharing
@@ -105,6 +107,8 @@ struct bpf_map {
 	atomic_t usercnt;
 	struct work_struct work;
 	char name[BPF_OBJ_NAME_LEN];
+	struct mutex freeze_mutex;
+	int writecnt; /* writable mmap cnt; protected by freeze_mutex */
 };
 
 static inline bool map_value_has_spin_lock(const struct bpf_map *map)
@@ -461,8 +465,8 @@ struct bpf_array {
 	 */
 	enum bpf_prog_type owner_prog_type;
 	bool owner_jited;
+	void *value;
 	union {
-		char value[0] __aligned(8);
 		void *ptrs[0] __aligned(8);
 		void __percpu *pptrs[0] __aligned(8);
 	};
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index df6809a76404..bb39b53622d9 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -346,6 +346,9 @@ enum bpf_attach_type {
 /* Clone map from listener for newly accepted socket */
 #define BPF_F_CLONE		(1U << 9)
 
+/* Enable memory-mapping BPF map */
+#define BPF_F_MMAPABLE		(1U << 10)
+
 /* flags for BPF_PROG_QUERY */
 #define BPF_F_QUERY_EFFECTIVE	(1U << 0)
 
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 1c65ce0098a9..3264a7318ff7 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -14,7 +14,7 @@
 #include "map_in_map.h"
 
 #define ARRAY_CREATE_FLAG_MASK \
-	(BPF_F_NUMA_NODE | BPF_F_ACCESS_MASK)
+	(BPF_F_NUMA_NODE | BPF_F_MMAPABLE | BPF_F_ACCESS_MASK)
 
 static void bpf_array_free_percpu(struct bpf_array *array)
 {
@@ -55,8 +55,11 @@ int array_map_alloc_check(union bpf_attr *attr)
 	if (attr->max_entries == 0 || attr->key_size != 4 ||
 	    attr->value_size == 0 ||
 	    attr->map_flags & ~ARRAY_CREATE_FLAG_MASK ||
-	    !bpf_map_flags_access_ok(attr->map_flags) ||
-	    (percpu && numa_node != NUMA_NO_NODE))
+	    !bpf_map_flags_access_ok(attr->map_flags))
+		return -EINVAL;
+
+	if (percpu && (numa_node != NUMA_NO_NODE ||
+		       attr->map_flags & BPF_F_MMAPABLE))
 		return -EINVAL;
 
 	if (attr->value_size > KMALLOC_MAX_SIZE)
@@ -74,7 +77,7 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
 	int ret, numa_node = bpf_map_attr_numa_node(attr);
 	u32 elem_size, index_mask, max_entries;
 	bool unpriv = !capable(CAP_SYS_ADMIN);
-	u64 cost, array_size, mask64;
+	u64 cost, array_size, data_size, mask64;
 	struct bpf_map_memory mem;
 	struct bpf_array *array;
 
@@ -102,13 +105,20 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
 	}
 
 	array_size = sizeof(*array);
-	if (percpu)
+	data_size = 0;
+	if (percpu) {
 		array_size += (u64) max_entries * sizeof(void *);
-	else
-		array_size += (u64) max_entries * elem_size;
+	} else {
+		if (attr->map_flags & BPF_F_MMAPABLE) {
+			data_size = (u64) max_entries * elem_size;
+			data_size = round_up(data_size, PAGE_SIZE);
+		} else {
+			array_size += (u64) max_entries * elem_size;
+		}
+	}
 
 	/* make sure there is no u32 overflow later in round_up() */
-	cost = array_size;
+	cost = array_size + data_size;
 	if (percpu)
 		cost += (u64)attr->max_entries * elem_size * num_possible_cpus();
 
@@ -122,6 +132,19 @@ static struct bpf_map *array_map_alloc(union bpf_attr *attr)
 		bpf_map_charge_finish(&mem);
 		return ERR_PTR(-ENOMEM);
 	}
+	array->value = (void *)array + sizeof(*array);
+
+	if (attr->map_flags & BPF_F_MMAPABLE) {
+		void *data = vzalloc_node(data_size, numa_node);
+
+		if (!data) {
+			bpf_map_charge_finish(&mem);
+			bpf_map_area_free(array);
+			return ERR_PTR(-ENOMEM);
+		}
+		array->value = data;
+	}
+
 	array->index_mask = index_mask;
 	array->map.unpriv_array = unpriv;
 
@@ -365,6 +388,8 @@ static void array_map_free(struct bpf_map *map)
 	if (array->map.map_type == BPF_MAP_TYPE_PERCPU_ARRAY)
 		bpf_array_free_percpu(array);
 
+	if (array->map.map_flags & BPF_F_MMAPABLE)
+		kvfree(array->value);
 	bpf_map_area_free(array);
 }
 
@@ -444,6 +469,60 @@ static int array_map_check_btf(const struct bpf_map *map,
 	return 0;
 }
 
+void array_map_mmap_close(struct vm_area_struct *vma)
+{
+	struct bpf_array *array = vma->vm_file->private_data;
+
+	mutex_lock(&array->map.freeze_mutex);
+	if (vma->vm_flags & VM_WRITE)
+		array->map.writecnt--;
+	mutex_unlock(&array->map.freeze_mutex);
+
+	bpf_map_put_with_uref(&array->map);
+}
+
+static vm_fault_t array_map_mmap_fault(struct vm_fault *vmf)
+{
+	struct bpf_array *array = vmf->vma->vm_file->private_data;
+	void *p = array->value + (vmf->pgoff << PAGE_SHIFT);
+
+	vmf->page = vmalloc_to_page(p);
+	/* bump page refcount, it will be decremented by kernel on unmap */
+	get_page(vmf->page);
+
+	return 0;
+}
+
+static const struct vm_operations_struct array_map_vmops = {
+	.close		= array_map_mmap_close,
+	.fault		= array_map_mmap_fault,
+};
+
+int array_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
+{
+	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	u64 data_size, vma_size;
+
+	if (!(map->map_flags & BPF_F_MMAPABLE))
+		return -EINVAL;
+
+	data_size = (u64)array->elem_size * map->max_entries;
+	data_size = round_up(data_size, PAGE_SIZE);
+	vma_size = vma->vm_end - vma->vm_start;
+	if (vma_size != data_size)
+		return -EINVAL;
+
+	map = bpf_map_inc(map, true);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+
+	vma->vm_ops = &array_map_vmops;
+	vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND;
+	vma->vm_private_data = array;
+
+	return 0;
+}
+
 const struct bpf_map_ops array_map_ops = {
 	.map_alloc_check = array_map_alloc_check,
 	.map_alloc = array_map_alloc,
@@ -455,6 +534,7 @@ const struct bpf_map_ops array_map_ops = {
 	.map_gen_lookup = array_map_gen_lookup,
 	.map_direct_value_addr = array_map_direct_value_addr,
 	.map_direct_value_meta = array_map_direct_value_meta,
+	.map_mmap = array_map_mmap,
 	.map_seq_show_elem = array_map_seq_show_elem,
 	.map_check_btf = array_map_check_btf,
 };
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6d9ce95e5a8d..a64d3b0d7201 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -425,6 +425,35 @@ static ssize_t bpf_dummy_write(struct file *filp, const char __user *buf,
 	return -EINVAL;
 }
 
+static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+	struct bpf_map *map = filp->private_data;
+	int err;
+
+	if (!map->ops->map_mmap || map_value_has_spin_lock(map))
+		return -ENOTSUPP;
+
+	if (!(vma->vm_flags & VM_SHARED))
+		return -EINVAL;
+
+	mutex_lock(&map->freeze_mutex);
+
+	if ((vma->vm_flags & VM_WRITE) && map->frozen) {
+		err = -EPERM;
+		goto out;
+	}
+
+	err = map->ops->map_mmap(map, vma);
+	if (err)
+		goto out;
+
+	if (vma->vm_flags & VM_WRITE)
+		map->writecnt++;
+out:
+	mutex_unlock(&map->freeze_mutex);
+	return err;
+}
+
 const struct file_operations bpf_map_fops = {
 #ifdef CONFIG_PROC_FS
 	.show_fdinfo	= bpf_map_show_fdinfo,
@@ -432,6 +461,7 @@ const struct file_operations bpf_map_fops = {
 	.release	= bpf_map_release,
 	.read		= bpf_dummy_read,
 	.write		= bpf_dummy_write,
+	.mmap		= bpf_map_mmap,
 };
 
 int bpf_map_new_fd(struct bpf_map *map, int flags)
@@ -577,6 +607,7 @@ static int map_create(union bpf_attr *attr)
 
 	atomic_set(&map->refcnt, 1);
 	atomic_set(&map->usercnt, 1);
+	mutex_init(&map->freeze_mutex);
 
 	if (attr->btf_key_type_id || attr->btf_value_type_id) {
 		struct btf *btf;
@@ -1173,6 +1204,13 @@ static int map_freeze(const union bpf_attr *attr)
 	map = __bpf_map_get(f);
 	if (IS_ERR(map))
 		return PTR_ERR(map);
+
+	mutex_lock(&map->freeze_mutex);
+
+	if (map->writecnt) {
+		err = -EBUSY;
+		goto err_put;
+	}
 	if (READ_ONCE(map->frozen)) {
 		err = -EBUSY;
 		goto err_put;
@@ -1184,6 +1222,7 @@ static int map_freeze(const union bpf_attr *attr)
 
 	WRITE_ONCE(map->frozen, true);
 err_put:
+	mutex_unlock(&map->freeze_mutex);
 	fdput(f);
 	return err;
 }
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index df6809a76404..bb39b53622d9 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -346,6 +346,9 @@ enum bpf_attach_type {
 /* Clone map from listener for newly accepted socket */
 #define BPF_F_CLONE		(1U << 9)
 
+/* Enable memory-mapping BPF map */
+#define BPF_F_MMAPABLE		(1U << 10)
+
 /* flags for BPF_PROG_QUERY */
 #define BPF_F_QUERY_EFFECTIVE	(1U << 0)
 
-- 
2.17.1

Re: [PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY

[Song Liu]

> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> Add ability to memory-map contents of BPF array map. This is extremely useful
> for working with BPF global data from userspace programs. It allows to avoid
> typical bpf_map_{lookup,update}_elem operations, improving both performance
> and usability.
> 
> There had to be special considerations for map freezing, to avoid having
> writable memory view into a frozen map. To solve this issue, map freezing and
> mmap-ing is happening under mutex now:
>  - if map is already frozen, no writable mapping is allowed;
>  - if map has writable memory mappings active (accounted in map->writecnt),
>    map freezing will keep failing with -EBUSY;
>  - once number of writable memory mappings drops to zero, map freezing can be
>    performed again.
> 
> Only non-per-CPU arrays are supported right now. Maps with spinlocks can't be
> memory mapped either.
> 
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

With one nit below. 


[...]

> -	if (percpu)
> +	data_size = 0;
> +	if (percpu) {
> 		array_size += (u64) max_entries * sizeof(void *);
> -	else
> -		array_size += (u64) max_entries * elem_size;

> +	} else {
> +		if (attr->map_flags & BPF_F_MMAPABLE) {
> +			data_size = (u64) max_entries * elem_size;
> +			data_size = round_up(data_size, PAGE_SIZE);
> +		} else {
> +			array_size += (u64) max_entries * elem_size;
> +		}
> +	}
> 
> 	/* make sure there is no u32 overflow later in round_up() */
> -	cost = array_size;
> +	cost = array_size + data_size;



This is a little confusing. Maybe we can do 

	data_size = (u64) max_entries * (per_cpu ? sizeof(void *) : elem_size;
	if (attr->map_flags & BPF_F_MMAPABLE)
		data_size = round_up(data_size, PAGE_SIZE);
	
	cost = array_size + data_size;

So we use data_size in all cases. 

Maybe also rename array_size.


> 	if (percpu)
> 		cost += (u64)attr->max_entries * elem_size * num_possible_cpus();

And maybe we can also include this in data_size. 

[...]

Re: [PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY

[Andrii Nakryiko]

On Thu, Nov 7, 2019 at 10:39 PM Song Liu <songliubraving@fb.com> wrote:
>
>
>
> > On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> >
> > Add ability to memory-map contents of BPF array map. This is extremely useful
> > for working with BPF global data from userspace programs. It allows to avoid
> > typical bpf_map_{lookup,update}_elem operations, improving both performance
> > and usability.
> >
> > There had to be special considerations for map freezing, to avoid having
> > writable memory view into a frozen map. To solve this issue, map freezing and
> > mmap-ing is happening under mutex now:
> >  - if map is already frozen, no writable mapping is allowed;
> >  - if map has writable memory mappings active (accounted in map->writecnt),
> >    map freezing will keep failing with -EBUSY;
> >  - once number of writable memory mappings drops to zero, map freezing can be
> >    performed again.
> >
> > Only non-per-CPU arrays are supported right now. Maps with spinlocks can't be
> > memory mapped either.
> >
> > Cc: Rik van Riel <riel@surriel.com>
> > Cc: Johannes Weiner <hannes@cmpxchg.org>
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>
> Acked-by: Song Liu <songliubraving@fb.com>
>
> With one nit below.
>
>
> [...]
>
> > -     if (percpu)
> > +     data_size = 0;
> > +     if (percpu) {
> >               array_size += (u64) max_entries * sizeof(void *);
> > -     else
> > -             array_size += (u64) max_entries * elem_size;
>
> > +     } else {
> > +             if (attr->map_flags & BPF_F_MMAPABLE) {
> > +                     data_size = (u64) max_entries * elem_size;
> > +                     data_size = round_up(data_size, PAGE_SIZE);
> > +             } else {
> > +                     array_size += (u64) max_entries * elem_size;
> > +             }
> > +     }
> >
> >       /* make sure there is no u32 overflow later in round_up() */
> > -     cost = array_size;
> > +     cost = array_size + data_size;
>
>
>
> This is a little confusing. Maybe we can do
>

I don't think I can do that without even bigger code churn. In
non-mmap()-able case, array_size specifies the size of one chunk of
memory, which consists of sizeof(struct bpf_array) bytes, followed by
actual data. This is accomplished in one allocation. That's current
case for arrays.

For BPF_F_MMAPABLE case, though, we have to do 2 separate allocations,
to make sure that mmap()-able part is allocated with vmalloc() and is
page-aligned. So array_size keeps track of number of bytes allocated
for struct bpf_array plus, optionally, per-cpu or non-mmapable array
data, while data_size is explicitly for vmalloc()-ed mmap()-able chunk
of data. If not for this, I'd just keep adjusting array_size.

So the invariant for per-cpu and non-mmapable case is that data_size =
0, array_size = sizeof(struct bpf_array) + whatever amount of data we
need. For mmapable case: array_size = sizeof(struct bpf_array),
data_size = actual amount of array data.


>         data_size = (u64) max_entries * (per_cpu ? sizeof(void *) : elem_size;
>         if (attr->map_flags & BPF_F_MMAPABLE)
>                 data_size = round_up(data_size, PAGE_SIZE);
>
>         cost = array_size + data_size;
>
> So we use data_size in all cases.
>
> Maybe also rename array_size.
>
>
> >       if (percpu)
> >               cost += (u64)attr->max_entries * elem_size * num_possible_cpus();
>
> And maybe we can also include this in data_size.

see above.

>
> [...]
>

Re: [PATCH bpf-next 1/3] bpf: add mmap() support for BPF_MAP_TYPE_ARRAY

[Song Liu]

> On Nov 8, 2019, at 11:34 AM, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> 
> On Thu, Nov 7, 2019 at 10:39 PM Song Liu <songliubraving@fb.com> wrote:
>> 
>> 
>> 
>>> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
>>> 
>>> Add ability to memory-map contents of BPF array map. This is extremely useful
>>> for working with BPF global data from userspace programs. It allows to avoid
>>> typical bpf_map_{lookup,update}_elem operations, improving both performance
>>> and usability.
>>> 
>>> There had to be special considerations for map freezing, to avoid having
>>> writable memory view into a frozen map. To solve this issue, map freezing and
>>> mmap-ing is happening under mutex now:
>>> - if map is already frozen, no writable mapping is allowed;
>>> - if map has writable memory mappings active (accounted in map->writecnt),
>>>   map freezing will keep failing with -EBUSY;
>>> - once number of writable memory mappings drops to zero, map freezing can be
>>>   performed again.
>>> 
>>> Only non-per-CPU arrays are supported right now. Maps with spinlocks can't be
>>> memory mapped either.
>>> 
>>> Cc: Rik van Riel <riel@surriel.com>
>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>> Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>> 
>> Acked-by: Song Liu <songliubraving@fb.com>
>> 
>> With one nit below.
>> 
>> 
>> [...]
>> 
>>> -     if (percpu)
>>> +     data_size = 0;
>>> +     if (percpu) {
>>>              array_size += (u64) max_entries * sizeof(void *);
>>> -     else
>>> -             array_size += (u64) max_entries * elem_size;
>> 
>>> +     } else {
>>> +             if (attr->map_flags & BPF_F_MMAPABLE) {
>>> +                     data_size = (u64) max_entries * elem_size;
>>> +                     data_size = round_up(data_size, PAGE_SIZE);
>>> +             } else {
>>> +                     array_size += (u64) max_entries * elem_size;
>>> +             }
>>> +     }
>>> 
>>>      /* make sure there is no u32 overflow later in round_up() */
>>> -     cost = array_size;
>>> +     cost = array_size + data_size;
>> 
>> 
>> 
>> This is a little confusing. Maybe we can do
>> 
> 
> I don't think I can do that without even bigger code churn. In
> non-mmap()-able case, array_size specifies the size of one chunk of
> memory, which consists of sizeof(struct bpf_array) bytes, followed by
> actual data. This is accomplished in one allocation. That's current
> case for arrays.
> 
> For BPF_F_MMAPABLE case, though, we have to do 2 separate allocations,
> to make sure that mmap()-able part is allocated with vmalloc() and is
> page-aligned. So array_size keeps track of number of bytes allocated
> for struct bpf_array plus, optionally, per-cpu or non-mmapable array
> data, while data_size is explicitly for vmalloc()-ed mmap()-able chunk
> of data. If not for this, I'd just keep adjusting array_size.
> 
> So the invariant for per-cpu and non-mmapable case is that data_size =
> 0, array_size = sizeof(struct bpf_array) + whatever amount of data we
> need. For mmapable case: array_size = sizeof(struct bpf_array),
> data_size = actual amount of array data.

I see. Thanks for the explanation. 

Song

[PATCH bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible

[Andrii Nakryiko]

Add detection of BPF_F_MMAPABLE flag support for arrays and add it as an extra
flag to internal global data maps, if supported by kernel. This allows users
to memory-map global data and use it without BPF map operations, greatly
simplifying user experience.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fde6cb3e5d41..73607a31a068 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -142,6 +142,8 @@ struct bpf_capabilities {
 	__u32 btf_func:1;
 	/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
 	__u32 btf_datasec:1;
+	/* BPF_F_MMAPABLE is supported for arrays */
+	__u32 array_mmap:1;
 };
 
 /*
@@ -855,8 +857,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
 		pr_warn("failed to alloc map name\n");
 		return -ENOMEM;
 	}
-	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
-		 map_name, map->sec_idx, map->sec_offset);
 
 	def = &map->def;
 	def->type = BPF_MAP_TYPE_ARRAY;
@@ -864,6 +864,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
 	def->value_size = data->d_size;
 	def->max_entries = 1;
 	def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
+	if (obj->caps.array_mmap)
+		def->map_flags |= BPF_F_MMAPABLE;
+
+	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %u.\n",
+		 map_name, map->sec_idx, map->sec_offset, def->map_flags);
+
 	if (data_buff) {
 		*data_buff = malloc(data->d_size);
 		if (!*data_buff) {
@@ -2158,6 +2164,26 @@ static int bpf_object__probe_btf_datasec(struct bpf_object *obj)
 	return 0;
 }
 
+static int bpf_object__probe_array_mmap(struct bpf_object *obj)
+{
+	struct bpf_create_map_attr attr = {
+		.map_type = BPF_MAP_TYPE_ARRAY,
+		.map_flags = BPF_F_MMAPABLE,
+		.key_size = sizeof(int),
+		.value_size = sizeof(int),
+		.max_entries = 1,
+	};
+	int fd = bpf_create_map_xattr(&attr);
+
+	if (fd >= 0) {
+		obj->caps.array_mmap = 1;
+		close(fd);
+		return 1;
+	}
+
+	return 0;
+}
+
 static int
 bpf_object__probe_caps(struct bpf_object *obj)
 {
@@ -2166,6 +2192,7 @@ bpf_object__probe_caps(struct bpf_object *obj)
 		bpf_object__probe_global_data,
 		bpf_object__probe_btf_func,
 		bpf_object__probe_btf_datasec,
+		bpf_object__probe_array_mmap,
 	};
 	int i, ret;
 
-- 
2.17.1

Re: [PATCH bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible

[Song Liu]

> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> Add detection of BPF_F_MMAPABLE flag support for arrays and add it as an extra
> flag to internal global data maps, if supported by kernel. This allows users
> to memory-map global data and use it without BPF map operations, greatly
> simplifying user experience.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

With nit below. 

> ---
> tools/lib/bpf/libbpf.c | 31 +++++++++++++++++++++++++++++--
> 1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index fde6cb3e5d41..73607a31a068 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -142,6 +142,8 @@ struct bpf_capabilities {
> 	__u32 btf_func:1;
> 	/* BTF_KIND_VAR and BTF_KIND_DATASEC support */
> 	__u32 btf_datasec:1;
> +	/* BPF_F_MMAPABLE is supported for arrays */
> +	__u32 array_mmap:1;
> };
> 
> /*
> @@ -855,8 +857,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> 		pr_warn("failed to alloc map name\n");
> 		return -ENOMEM;
> 	}
> -	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
> -		 map_name, map->sec_idx, map->sec_offset);
> 
> 	def = &map->def;
> 	def->type = BPF_MAP_TYPE_ARRAY;
> @@ -864,6 +864,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> 	def->value_size = data->d_size;
> 	def->max_entries = 1;
> 	def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
> +	if (obj->caps.array_mmap)
> +		def->map_flags |= BPF_F_MMAPABLE;
> +
> +	pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %u.\n",

nit: Better print flags as %x. 

Re: [PATCH bpf-next 2/3] libbpf: make global data internal arrays mmap()-able, if possible

[Andrii Nakryiko]

On Thu, Nov 7, 2019 at 10:44 PM Song Liu <songliubraving@fb.com> wrote:
>
>
>
> > On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> >
> > Add detection of BPF_F_MMAPABLE flag support for arrays and add it as an extra
> > flag to internal global data maps, if supported by kernel. This allows users
> > to memory-map global data and use it without BPF map operations, greatly
> > simplifying user experience.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>
> Acked-by: Song Liu <songliubraving@fb.com>
>
> With nit below.
>
> > ---
> > tools/lib/bpf/libbpf.c | 31 +++++++++++++++++++++++++++++--
> > 1 file changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index fde6cb3e5d41..73607a31a068 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -142,6 +142,8 @@ struct bpf_capabilities {
> >       __u32 btf_func:1;
> >       /* BTF_KIND_VAR and BTF_KIND_DATASEC support */
> >       __u32 btf_datasec:1;
> > +     /* BPF_F_MMAPABLE is supported for arrays */
> > +     __u32 array_mmap:1;
> > };
> >
> > /*
> > @@ -855,8 +857,6 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> >               pr_warn("failed to alloc map name\n");
> >               return -ENOMEM;
> >       }
> > -     pr_debug("map '%s' (global data): at sec_idx %d, offset %zu.\n",
> > -              map_name, map->sec_idx, map->sec_offset);
> >
> >       def = &map->def;
> >       def->type = BPF_MAP_TYPE_ARRAY;
> > @@ -864,6 +864,12 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
> >       def->value_size = data->d_size;
> >       def->max_entries = 1;
> >       def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
> > +     if (obj->caps.array_mmap)
> > +             def->map_flags |= BPF_F_MMAPABLE;
> > +
> > +     pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %u.\n",
>
> nit: Better print flags as %x.
>
>

sure, will update

[PATCH bpf-next 3/3] selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests

[Andrii Nakryiko]

Add selftests validating mmap()-ing BPF array maps: both single-element and
multi-element ones. Also convert CO-RE relocation tests to use memory-mapped
views of global data.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 .../selftests/bpf/prog_tests/core_reloc.c     |  45 +++--
 tools/testing/selftests/bpf/prog_tests/mmap.c | 154 ++++++++++++++++++
 tools/testing/selftests/bpf/progs/test_mmap.c |  31 ++++
 3 files changed, 212 insertions(+), 18 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/mmap.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_mmap.c

diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc.c b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
index f94bd071536b..ec9e2fdd6b89 100644
--- a/tools/testing/selftests/bpf/prog_tests/core_reloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <test_progs.h>
 #include "progs/core_reloc_types.h"
+#include <sys/mman.h>
 
 #define STRUCT_TO_CHAR_PTR(struct_name) (const char *)&(struct struct_name)
 
@@ -453,8 +454,15 @@ struct data {
 	char out[256];
 };
 
+static size_t roundup_page(size_t sz)
+{
+	long page_size = sysconf(_SC_PAGE_SIZE);
+	return (sz + page_size - 1) / page_size * page_size;
+}
+
 void test_core_reloc(void)
 {
+	const size_t mmap_sz = roundup_page(sizeof(struct data));
 	struct bpf_object_load_attr load_attr = {};
 	struct core_reloc_test_case *test_case;
 	const char *tp_name, *probe_name;
@@ -463,8 +471,8 @@ void test_core_reloc(void)
 	struct bpf_map *data_map;
 	struct bpf_program *prog;
 	struct bpf_object *obj;
-	const int zero = 0;
-	struct data data;
+	struct data *data;
+	void *mmap_data = NULL;
 
 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
 		test_case = &test_cases[i];
@@ -476,8 +484,7 @@ void test_core_reloc(void)
 		);
 
 		obj = bpf_object__open_file(test_case->bpf_obj_file, &opts);
-		if (CHECK(IS_ERR_OR_NULL(obj), "obj_open",
-			  "failed to open '%s': %ld\n",
+		if (CHECK(IS_ERR(obj), "obj_open", "failed to open '%s': %ld\n",
 			  test_case->bpf_obj_file, PTR_ERR(obj)))
 			continue;
 
@@ -519,24 +526,22 @@ void test_core_reloc(void)
 		if (CHECK(!data_map, "find_data_map", "data map not found\n"))
 			goto cleanup;
 
-		memset(&data, 0, sizeof(data));
-		memcpy(data.in, test_case->input, test_case->input_len);
-
-		err = bpf_map_update_elem(bpf_map__fd(data_map),
-					  &zero, &data, 0);
-		if (CHECK(err, "update_data_map",
-			  "failed to update .data map: %d\n", err))
+		mmap_data = mmap(NULL, mmap_sz, PROT_READ | PROT_WRITE,
+				 MAP_SHARED, bpf_map__fd(data_map), 0);
+		if (CHECK(mmap_data == MAP_FAILED, "mmap",
+			  ".bss mmap failed: %d", errno)) {
+			mmap_data = NULL;
 			goto cleanup;
+		}
+		data = mmap_data;
+
+		memset(mmap_data, 0, sizeof(*data));
+		memcpy(data->in, test_case->input, test_case->input_len);
 
 		/* trigger test run */
 		usleep(1);
 
-		err = bpf_map_lookup_elem(bpf_map__fd(data_map), &zero, &data);
-		if (CHECK(err, "get_result",
-			  "failed to get output data: %d\n", err))
-			goto cleanup;
-
-		equal = memcmp(data.out, test_case->output,
+		equal = memcmp(data->out, test_case->output,
 			       test_case->output_len) == 0;
 		if (CHECK(!equal, "check_result",
 			  "input/output data don't match\n")) {
@@ -548,12 +553,16 @@ void test_core_reloc(void)
 			}
 			for (j = 0; j < test_case->output_len; j++) {
 				printf("output byte #%d: EXP 0x%02hhx GOT 0x%02hhx\n",
-				       j, test_case->output[j], data.out[j]);
+				       j, test_case->output[j], data->out[j]);
 			}
 			goto cleanup;
 		}
 
 cleanup:
+		if (mmap_data) {
+			CHECK_FAIL(munmap(mmap_data, mmap_sz));
+			mmap_data = NULL;
+		}
 		if (!IS_ERR_OR_NULL(link)) {
 			bpf_link__destroy(link);
 			link = NULL;
diff --git a/tools/testing/selftests/bpf/prog_tests/mmap.c b/tools/testing/selftests/bpf/prog_tests/mmap.c
new file mode 100644
index 000000000000..8c183b310d46
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/mmap.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include <sys/mman.h>
+
+struct map_data {
+	__u64 val[3];
+};
+
+struct bss_data {
+	__u64 in_val;
+	__u64 out_val;
+};
+
+static size_t roundup_page(size_t sz)
+{
+	long page_size = sysconf(_SC_PAGE_SIZE);
+	return (sz + page_size - 1) / page_size * page_size;
+}
+
+void test_mmap(void)
+{
+	const char *file = "test_mmap.o";
+	const char *probe_name = "raw_tracepoint/sys_enter";
+	const char *tp_name = "sys_enter";
+	const size_t bss_sz = roundup_page(sizeof(struct bss_data));
+	const size_t map_sz = roundup_page(sizeof(struct map_data));
+	int err, duration = 0, i, data_map_fd;
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	struct bpf_link *link = NULL;
+	struct bpf_map *data_map, *bss_map;
+	void *bss_mmaped = NULL, *map_mmaped = NULL, *tmp_mmaped;
+	volatile struct bss_data *bss_data;
+	volatile struct map_data *map_data;
+
+	obj = bpf_object__open_file("test_mmap.o", NULL);
+	if (CHECK(IS_ERR(obj), "obj_open", "failed to open '%s': %ld\n",
+		  file, PTR_ERR(obj)))
+		return;
+	prog = bpf_object__find_program_by_title(obj, probe_name);
+	if (CHECK(!prog, "find_probe", "prog '%s' not found\n", probe_name))
+		goto cleanup;
+	err = bpf_object__load(obj);
+	if (CHECK(err, "obj_load", "failed to load prog '%s': %d\n",
+		  probe_name, err))
+		goto cleanup;
+
+	bss_map = bpf_object__find_map_by_name(obj, "test_mma.bss");
+	if (CHECK(!bss_map, "find_bss_map", ".bss map not found\n"))
+		goto cleanup;
+	data_map = bpf_object__find_map_by_name(obj, "data_map");
+	if (CHECK(!data_map, "find_data_map", "data_map map not found\n"))
+		goto cleanup;
+	data_map_fd = bpf_map__fd(data_map);
+
+	bss_mmaped = mmap(NULL, bss_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
+			  bpf_map__fd(bss_map), 0);
+	if (CHECK(bss_mmaped == MAP_FAILED, "bss_mmap",
+		  ".bss mmap failed: %d\n", errno)) {
+		bss_mmaped = NULL;
+		goto cleanup;
+	}
+	/* map as R/W first */
+	map_mmaped = mmap(NULL, map_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
+			  data_map_fd, 0);
+	if (CHECK(map_mmaped == MAP_FAILED, "data_mmap",
+		  "data_map mmap failed: %d\n", errno)) {
+		map_mmaped = NULL;
+		goto cleanup;
+	}
+
+	bss_data = bss_mmaped;
+	map_data = map_mmaped;
+
+	CHECK_FAIL(bss_data->in_val);
+	CHECK_FAIL(bss_data->out_val);
+	CHECK_FAIL(map_data->val[0]);
+	CHECK_FAIL(map_data->val[1]);
+	CHECK_FAIL(map_data->val[2]);
+
+	link = bpf_program__attach_raw_tracepoint(prog, tp_name);
+	if (CHECK(IS_ERR(link), "attach_raw_tp", "err %ld\n", PTR_ERR(link)))
+		goto cleanup;
+
+	bss_data->in_val = 123;
+	usleep(1);
+	CHECK_FAIL(bss_data->in_val != 123);
+	CHECK_FAIL(bss_data->out_val != 123);
+	CHECK_FAIL(map_data->val[2] != 123);
+
+	/* data_map freeze should fail due to R/W mmap() */
+	err = bpf_map_freeze(data_map_fd);
+	if (CHECK(!err || errno != EBUSY, "no_freeze",
+		  "data_map freeze succeeded: err=%d, errno=%d\n", err, errno))
+		goto cleanup;
+
+	/* unmap R/W mapping */
+	err = munmap(map_mmaped, map_sz);
+	map_mmaped = NULL;
+	if (CHECK(err, "data_map_munmap", "data_map munmap failed: %d\n", errno))
+		goto cleanup;
+
+	/* re-map as R/O now */
+	map_mmaped = mmap(NULL, map_sz, PROT_READ, MAP_SHARED, data_map_fd, 0);
+	if (CHECK(map_mmaped == MAP_FAILED, "data_mmap",
+		  "data_map R/O mmap failed: %d\n", errno)) {
+		map_mmaped = NULL;
+		goto cleanup;
+	}
+	map_data = map_mmaped;
+
+	/* map/unmap in a loop to test ref counting */
+	for (i = 0; i < 10; i++) {
+		int flags = i % 2 ? PROT_READ : PROT_WRITE;
+		void *p;
+
+		p = mmap(NULL, map_sz, flags, MAP_SHARED, data_map_fd, 0);
+		if (CHECK_FAIL(p == MAP_FAILED))
+			goto cleanup;
+		err = munmap(p, map_sz);
+		if (CHECK_FAIL(err))
+			goto cleanup;
+	}
+
+	/* data_map freeze should now succeed due to no R/W mapping */
+	err = bpf_map_freeze(data_map_fd);
+	if (CHECK(err, "freeze", "data_map freeze failed: err=%d, errno=%d\n",
+		  err, errno))
+		goto cleanup;
+
+	/* mapping as R/W now should fail */
+	tmp_mmaped = mmap(NULL, map_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
+			  data_map_fd, 0);
+	if (CHECK(tmp_mmaped != MAP_FAILED, "data_mmap",
+		  "data_map mmap succeeded\n")) {
+		munmap(tmp_mmaped, map_sz);
+		goto cleanup;
+	}
+
+	bss_data->in_val = 321;
+	usleep(1);
+	CHECK_FAIL(bss_data->in_val != 321);
+	CHECK_FAIL(bss_data->out_val != 321);
+	CHECK_FAIL(map_data->val[2] != 321);
+
+cleanup:
+	if (bss_mmaped)
+		CHECK_FAIL(munmap(bss_mmaped, bss_sz));
+	if (map_mmaped)
+		CHECK_FAIL(munmap(map_mmaped, map_sz));
+	if (!IS_ERR_OR_NULL(link))
+		bpf_link__destroy(link);
+	bpf_object__close(obj);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_mmap.c b/tools/testing/selftests/bpf/progs/test_mmap.c
new file mode 100644
index 000000000000..22bd5f042332
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_mmap.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <linux/bpf.h>
+#include <stdint.h>
+#include "bpf_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 3);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__type(key, __u32);
+	__type(value, __u64);
+} data_map SEC(".maps");
+
+static volatile __u64 in_val;
+static volatile __u64 out_val;
+
+SEC("raw_tracepoint/sys_enter")
+int test_mmap(void *ctx)
+{
+	int idx = 2;
+
+	out_val = in_val;
+	bpf_map_update_elem(&data_map, &idx, (const void *)&in_val, 0);
+
+	return 0;
+}
+
-- 
2.17.1

Re: [PATCH bpf-next 3/3] selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests

[Song Liu]

> On Nov 7, 2019, at 8:20 PM, Andrii Nakryiko <andriin@fb.com> wrote:
> 
> Add selftests validating mmap()-ing BPF array maps: both single-element and
> multi-element ones. Also convert CO-RE relocation tests to use memory-mapped
> views of global data.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Song Liu <songliubraving@fb.com>

Re: [PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps

[Stanislav Fomichev]

On 11/07, Andrii Nakryiko wrote:
> This patch set adds ability to memory-map BPF array maps (single- and
> multi-element). The primary use case is memory-mapping BPF array maps, created
> to back global data variables, created by libbpf implicitly. This allows for
> much better usability, along with avoiding syscalls to read or update data
> completely.
Just wondering: is it something that you plan to extend to other map types?

Re: [PATCH bpf-next 0/3] Add support for memory-mapping BPF array maps

[Andrii Nakryiko]

On Fri, Nov 8, 2019 at 2:08 PM Stanislav Fomichev <sdf@fomichev.me> wrote:
>
> On 11/07, Andrii Nakryiko wrote:
> > This patch set adds ability to memory-map BPF array maps (single- and
> > multi-element). The primary use case is memory-mapping BPF array maps, created
> > to back global data variables, created by libbpf implicitly. This allows for
> > much better usability, along with avoiding syscalls to read or update data
> > completely.
> Just wondering: is it something that you plan to extend to other map types?

My main motivation is global data, so normal arrays are the most
important for me. If anyone has any performance-driven use cases, we
can extend others as well, if possible. Not all maps can be easily
mmap()'ed just due to nature of their data. E.g., it's hard to imagine
how hashmap can be mapped. But doing per-cpu arrays should be doable
with good kernel-userspace memory layout "contract".