On Thu, May 1, 2025 at 7:28 AM Lorenz Bauer lmb@isovalent.com wrote:
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);
Probably should set VM_DONTDUMP to avoid being in the core dump. vm_flags_mod() can set and clear in one operation.
return vm_iomap_memory(vma, virt_to_phys(__start_BTF), btf_size);
and this one should probably be vm_insert_pages(). Since it's not an IO area.
Overall I think it's a good idea. As Daniel suggested pls make use of it in libbpf too. That exercise will make sure that feature probing works with fallback.
pw-bot: cr