* [PATCH bpf-next 1/2] btf: allow mmap of vmlinux btf
2025-05-01 14:28 [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux Lorenz Bauer
@ 2025-05-01 14:28 ` Lorenz Bauer
2025-05-01 20:26 ` Alexei Starovoitov
2025-05-01 14:28 ` [PATCH bpf-next 2/2] selftests: bpf: add a test for mmapable vmlinux BTF Lorenz Bauer
2025-05-01 15:58 ` [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux Daniel Xu
2 siblings, 1 reply; 6+ messages in thread
From: Lorenz Bauer @ 2025-05-01 14:28 UTC (permalink / raw)
To: Arnd Bergmann, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman, Song Liu,
Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev,
Hao Luo, Jiri Olsa, Mykola Lysenko, Shuah Khan
Cc: linux-arch, linux-kernel, bpf, linux-kselftest, Lorenz Bauer
User space needs access to kernel BTF for many modern features of BPF.
Right now each process needs to read the BTF blob either in pieces or
as a whole. Allow mmaping the sysfs file so that processes can directly
access the memory allocated for it in the kernel.
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
include/asm-generic/vmlinux.lds.h | 3 ++-
kernel/bpf/sysfs_btf.c | 25 +++++++++++++++++++++++--
2 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 58a635a6d5bdf0c53c267c2a3d21a5ed8678ce73..1750390735fac7637cc4d2fa05f96cb2a36aa448 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -667,10 +667,11 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
*/
#ifdef CONFIG_DEBUG_INFO_BTF
#define BTF \
+ . = ALIGN(PAGE_SIZE); \
.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) { \
BOUNDED_SECTION_BY(.BTF, _BTF) \
} \
- . = ALIGN(4); \
+ . = ALIGN(PAGE_SIZE); \
.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) { \
*(.BTF_ids) \
}
diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 81d6cf90584a7157929c50f62a5c6862e7a3d081..7651f37b82c78b8afd96078567a5b6612f5f4d97 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -7,18 +7,39 @@
#include <linux/kobject.h>
#include <linux/init.h>
#include <linux/sysfs.h>
+#include <linux/mm.h>
+#include <linux/io.h>
/* See scripts/link-vmlinux.sh, gen_btf() func for details */
extern char __start_BTF[];
extern char __stop_BTF[];
+struct kobject *btf_kobj;
+
+static int btf_vmlinux_mmap(struct file *filp, struct kobject *kobj,
+ const struct bin_attribute *attr,
+ struct vm_area_struct *vma)
+{
+ size_t btf_size = __stop_BTF - __start_BTF;
+
+ if (kobj != btf_kobj)
+ return -EINVAL;
+
+ if (vma->vm_flags & (VM_WRITE|VM_EXEC|VM_MAYSHARE))
+ return -EACCES;
+
+ vm_flags_clear(vma, VM_MAYEXEC);
+ vm_flags_clear(vma, VM_MAYWRITE);
+
+ return vm_iomap_memory(vma, virt_to_phys(__start_BTF), btf_size);
+}
+
static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
.attr = { .name = "vmlinux", .mode = 0444, },
.read_new = sysfs_bin_attr_simple_read,
+ .mmap = btf_vmlinux_mmap,
};
-struct kobject *btf_kobj;
-
static int __init btf_vmlinux_init(void)
{
bin_attr_btf_vmlinux.private = __start_BTF;
--
2.49.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH bpf-next 2/2] selftests: bpf: add a test for mmapable vmlinux BTF
2025-05-01 14:28 [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux Lorenz Bauer
2025-05-01 14:28 ` [PATCH bpf-next 1/2] btf: allow mmap of vmlinux btf Lorenz Bauer
@ 2025-05-01 14:28 ` Lorenz Bauer
2025-05-01 15:58 ` [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux Daniel Xu
2 siblings, 0 replies; 6+ messages in thread
From: Lorenz Bauer @ 2025-05-01 14:28 UTC (permalink / raw)
To: Arnd Bergmann, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman, Song Liu,
Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev,
Hao Luo, Jiri Olsa, Mykola Lysenko, Shuah Khan
Cc: linux-arch, linux-kernel, bpf, linux-kselftest, Lorenz Bauer
Add a basic test for the ability to mmap /sys/kernel/btf/vmlinux. Since
libbpf doesn't have an API to parse BTF from memory we do some basic
sanity checks ourselves.
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
tools/testing/selftests/bpf/prog_tests/btf_sysfs.c | 79 ++++++++++++++++++++++
1 file changed, 79 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
new file mode 100644
index 0000000000000000000000000000000000000000..8dffed136b4757779028ec0971b56ff541f2218c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/* Copyright (c) 2025 Isovalent */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define BTF_MAGIC 0xeB9F
+
+static const char *btf_path = "/sys/kernel/btf/vmlinux";
+
+void test_btf_sysfs(void)
+{
+ struct stat st;
+ __u64 btf_size;
+ void *raw_data = NULL;
+ int fd = -1;
+ size_t trailing;
+ long page_size;
+
+ page_size = sysconf(_SC_PAGESIZE);
+ if (!ASSERT_GE(page_size, 0, "get_page_size"))
+ goto cleanup;
+
+ if (!ASSERT_OK(stat(btf_path, &st), "stat_btf"))
+ goto cleanup;
+
+ btf_size = st.st_size;
+ trailing = page_size - (btf_size % page_size) % page_size;
+
+ fd = open(btf_path, O_RDONLY);
+ if (!ASSERT_GE(fd, 0, "open_btf"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_writable"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ, MAP_SHARED, fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_shared"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size + trailing + 1, PROT_READ, MAP_PRIVATE, fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_invalid_size"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ, MAP_PRIVATE, fd, 0);
+ if (!ASSERT_NEQ(raw_data, MAP_FAILED, "mmap_btf"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_WRITE), -1,
+ "mprotect_writable"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_EXEC), -1,
+ "mprotect_executable"))
+ goto cleanup;
+
+ /* Check BTF magic value */
+ if (!ASSERT_EQ(*(__u16 *)raw_data, BTF_MAGIC, "btf_magic"))
+ goto cleanup;
+
+ /* Check padding is zeroed */
+ for (int i = 0; i < trailing; i++) {
+ if (((__u8 *)raw_data)[btf_size + i] != 0) {
+ PRINT_FAIL("tail of BTF is not zero at page offset %d\n", i);
+ goto cleanup;
+ }
+ }
+
+cleanup:
+ if (raw_data && raw_data != MAP_FAILED)
+ munmap(raw_data, btf_size);
+ if (fd >= 0)
+ close(fd);
+}
--
2.49.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux
2025-05-01 14:28 [PATCH bpf-next 0/2] Allow mmap of /sys/kernel/btf/vmlinux Lorenz Bauer
2025-05-01 14:28 ` [PATCH bpf-next 1/2] btf: allow mmap of vmlinux btf Lorenz Bauer
2025-05-01 14:28 ` [PATCH bpf-next 2/2] selftests: bpf: add a test for mmapable vmlinux BTF Lorenz Bauer
@ 2025-05-01 15:58 ` Daniel Xu
2 siblings, 0 replies; 6+ messages in thread
From: Daniel Xu @ 2025-05-01 15:58 UTC (permalink / raw)
To: Lorenz Bauer, Arnd Bergmann, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman, Song Liu,
Yonghong Song, John Fastabend, KP Singh, Stanislav Fomichev,
Hao Luo, Jiri Olsa, Mykola Lysenko, Shuah Khan
Cc: linux-arch, linux-kernel, bpf@vger.kernel.org, linux-kselftest
On Thu, May 1, 2025, at 7:28 AM, Lorenz Bauer wrote:
> I'd like to cut down the memory usage of parsing vmlinux BTF in ebpf-go.
> With some upcoming changes the library is sitting at 5MiB for a parse.
> Most of that memory is simply copying the BTF blob into user space.
> By allowing vmlinux BTF to be mmapped read-only into user space I can
> cut memory usage by about 75%.
Cool! Maybe teach libbpf to use this as well? So everyone else can pick up
the win transparently.
>
> Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
> ---
> Lorenz Bauer (2):
> btf: allow mmap of vmlinux btf
> selftests: bpf: add a test for mmapable vmlinux BTF
>
> include/asm-generic/vmlinux.lds.h | 3 +-
> kernel/bpf/sysfs_btf.c | 25 ++++++-
> tools/testing/selftests/bpf/prog_tests/btf_sysfs.c | 79 ++++++++++++++++++++++
> 3 files changed, 104 insertions(+), 3 deletions(-)
> ---
> base-commit: 38d976c32d85ef12dcd2b8a231196f7049548477
> change-id: 20250501-vmlinux-mmap-2ec5563c3ef1
>
> Best regards,
> --
> Lorenz Bauer <lmb@isovalent.com>
^ permalink raw reply [flat|nested] 6+ messages in thread