Re: [PATCH bpf-next 6/8] bpf: Add arch_bpf_trampoline_size()

Jiri Olsa
2023-09-21T17:09:36Z

On Tue, Sep 19, 2023 at 10:31:56PM -0700, Song Liu wrote:

SNIP

> bool bpf_jit_supports_subprog_tailcalls(void)
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 5f7528cac344..eca561621e65 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2422,10 +2422,10 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog,
> * add rsp, 8 // skip eth_type_trans's frame
> * ret // return to its caller
> */
> -int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
> - const struct btf_func_model *m, u32 flags,
> - struct bpf_tramp_links *tlinks,
> - void *func_addr)
> +static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
> + const struct btf_func_model *m, u32 flags,
> + struct bpf_tramp_links *tlinks,
> + void *func_addr)
> {

hum, I dont understand what's the __arch_prepare_bpf_trampoline for,
could we have just the arch_prepare_bpf_trampoline?

jirka

> int i, ret, nr_regs = m->nr_args, stack_size = 0;
> int regs_off, nregs_off, ip_off, run_ctx_off, arg_stack_off, rbx_off;
> @@ -2678,6 +2678,38 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i
> return ret;
> }
>
> +int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *image_end,
> + const struct btf_func_model *m, u32 flags,
> + struct bpf_tramp_links *tlinks,
> + void *func_addr)
> +{
> + return __arch_prepare_bpf_trampoline(im, image, image_end, m, flags, tlinks, func_addr);
> +}
> +
> +int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> + struct bpf_tramp_links *tlinks, void *func_addr)
> +{
> + struct bpf_tramp_image im;
> + void *image;
> + int ret;
> +
> + /* Allocate a temporary buffer for __arch_prepare_bpf_trampoline().
> + * This will NOT cause fragmentation in direct map, as we do not
> + * call set_memory_*() on this buffer.
> + */
> + image = bpf_jit_alloc_exec(PAGE_SIZE);
> + if (!image)
> + return -ENOMEM;
> +
> + ret = __arch_prepare_bpf_trampoline(&im, image, image + PAGE_SIZE, m, flags,
> + tlinks, func_addr);
> + bpf_jit_free_exec(image);
> + if (ret < 0)
> + return ret;
> +
> + return ret;
> +}
> +
> static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs, u8 *image, u8 *buf)
> {
> u8 *jg_reloc, *prog = *pprog;
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 548f3ef34ba1..5bbac549b0a0 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1087,6 +1087,8 @@ void *arch_alloc_bpf_trampoline(int size);
> void arch_free_bpf_trampoline(void *image, int size);
> void arch_protect_bpf_trampoline(void *image, int size);
> void arch_unprotect_bpf_trampoline(void *image, int size);
> +int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> + struct bpf_tramp_links *tlinks, void *func_addr);
>
> u64 notrace __bpf_prog_enter_sleepable_recur(struct bpf_prog *prog,
> struct bpf_tramp_run_ctx *run_ctx);
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 5509bdf98067..285c5b7c1ea4 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -1070,6 +1070,12 @@ void __weak arch_unprotect_bpf_trampoline(void *image, int size)
> set_memory_rw((long)image, 1);
> }
>
> +int __weak arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags,
> + struct bpf_tramp_links *tlinks, void *func_addr)
> +{
> + return -ENOTSUPP;
> +}
> +
> static int __init init_trampolines(void)
> {
> int i;
> --
> 2.34.1
>
>