[PATCH v3 1/2] powerpc64/bpf: Implement fsession support
Hari Bathini
hbathini at linux.ibm.com
Wed Apr 1 23:08:14 AEDT 2026
On 01/04/26 7:40 pm, adubey at linux.ibm.com wrote:
> From: Abhishek Dubey <adubey at linux.ibm.com>
>
> Implement JIT support for fsession in powerpc64 trampoline.
> The trampoline stack now accommodate session cookies and
> function metadata in place of function argument. fentry/fexit
> programs consume corresponding function metadata. This mirrors
> existing x86 behavior and enable session cookies on powerpc64.
>
> # ./test_progs -t fsession
> #135/1 fsession_test/fsession_test:OK
> #135/2 fsession_test/fsession_reattach:OK
> #135/3 fsession_test/fsession_cookie:OK
> #135 fsession_test:OK
> Summary: 1/3 PASSED, 0 SKIPPED, 0 FAILED
>
Looks good to me.
Acked-by: Hari Bathini <hbathini at linux.ibm.com>
> Signed-off-by: Abhishek Dubey <adubey at linux.ibm.com>
> Tested-by: Venkat Rao Bagalkote <venkat88 at linux.ibm.com>
> ---
>
> This patch is rebased over https://lore.kernel.org/bpf/20260401103215.104438-1-adubey@linux.ibm.com
>
> v2->v3:
> Rebased over latest changes
> Collected Tested-by tag
> v1->v2:
> No change since v1
>
> [v2]: https://lore.kernel.org/bpf/20260226041217.18059-1-adubey@linux.ibm.com
> [v1]: https://lore.kernel.org/bpf/20260216155310.38457-1-adubey@linux.ibm.com
>
> arch/powerpc/net/bpf_jit.h | 4 +-
> arch/powerpc/net/bpf_jit_comp.c | 69 ++++++++++++++++++++++++++-----
> arch/powerpc/net/bpf_jit_comp64.c | 25 +++++++++++
> 3 files changed, 87 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit.h b/arch/powerpc/net/bpf_jit.h
> index a232f3fb73be..f32de8704d4d 100644
> --- a/arch/powerpc/net/bpf_jit.h
> +++ b/arch/powerpc/net/bpf_jit.h
> @@ -218,7 +218,9 @@ void bpf_jit_build_epilogue(u32 *image, struct codegen_context *ctx);
> void bpf_jit_build_fentry_stubs(u32 *image, struct codegen_context *ctx);
> void bpf_jit_realloc_regs(struct codegen_context *ctx);
> int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr);
> -
> +void prepare_for_fsession_fentry(u32 *image, struct codegen_context *ctx, int cookie_cnt,
> + int cookie_off, int retval_off);
> +void store_func_meta(u32 *image, struct codegen_context *ctx, u64 func_meta, int func_meta_off);
> int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, u32 *fimage, int pass,
> struct codegen_context *ctx, int insn_idx,
> int jmp_off, int dst_reg, u32 code);
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 2018260f56c6..16d15ff3145a 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -540,6 +540,11 @@ bool bpf_jit_supports_private_stack(void)
> return IS_ENABLED(CONFIG_PPC64);
> }
>
> +bool bpf_jit_supports_fsession(void)
> +{
> + return IS_ENABLED(CONFIG_PPC64);
> +}
> +
> bool bpf_jit_supports_arena(void)
> {
> return IS_ENABLED(CONFIG_PPC64);
> @@ -812,12 +817,16 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> struct bpf_tramp_links *tlinks,
> void *func_addr)
> {
> - int regs_off, nregs_off, ip_off, run_ctx_off, retval_off, nvr_off, alt_lr_off, r4_off = 0;
> + int regs_off, func_meta_off, ip_off, run_ctx_off, retval_off;
> + int nvr_off, alt_lr_off, r4_off = 0;
> struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
> struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
> struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
> int i, ret, nr_regs, retaddr_off, bpf_frame_size = 0;
> struct codegen_context codegen_ctx, *ctx;
> + int cookie_off, cookie_cnt, cookie_ctx_off;
> + int fsession_cnt = bpf_fsession_cnt(tlinks);
> + u64 func_meta;
> u32 *image = (u32 *)rw_image;
> ppc_inst_t branch_insn;
> u32 *branches = NULL;
> @@ -853,9 +862,11 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> * [ reg argN ]
> * [ ... ]
> * regs_off [ reg_arg1 ] prog_ctx
> - * nregs_off [ args count ] ((u64 *)prog_ctx)[-1]
> + * func_meta_off [ args count ] ((u64 *)prog_ctx)[-1]
> * ip_off [ traced function ] ((u64 *)prog_ctx)[-2]
> + * [ stack cookieN ]
> * [ ... ]
> + * cookie_off [ stack cookie1 ]
> * run_ctx_off [ bpf_tramp_run_ctx ]
> * [ reg argN ]
> * [ ... ]
> @@ -887,16 +898,21 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> run_ctx_off = bpf_frame_size;
> bpf_frame_size += round_up(sizeof(struct bpf_tramp_run_ctx), SZL);
>
> + /* room for session cookies */
> + cookie_off = bpf_frame_size;
> + cookie_cnt = bpf_fsession_cookie_cnt(tlinks);
> + bpf_frame_size += cookie_cnt * 8;
> +
> /* Room for IP address argument */
> ip_off = bpf_frame_size;
> if (flags & BPF_TRAMP_F_IP_ARG)
> bpf_frame_size += SZL;
>
> - /* Room for args count */
> - nregs_off = bpf_frame_size;
> + /* Room for function metadata, arg regs count */
> + func_meta_off = bpf_frame_size;
> bpf_frame_size += SZL;
>
> - /* Room for args */
> + /* Room for arg regs */
> regs_off = bpf_frame_size;
> bpf_frame_size += nr_regs * SZL;
>
> @@ -995,9 +1011,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> EMIT(PPC_RAW_STL(_R3, _R1, retaddr_off));
> }
>
> - /* Save function arg count -- see bpf_get_func_arg_cnt() */
> - EMIT(PPC_RAW_LI(_R3, nr_regs));
> - EMIT(PPC_RAW_STL(_R3, _R1, nregs_off));
> + /* Save function arg regs count -- see bpf_get_func_arg_cnt() */
> + func_meta = nr_regs;
> + store_func_meta(image, ctx, func_meta, func_meta_off);
>
> /* Save nv regs */
> EMIT(PPC_RAW_STL(_R25, _R1, nvr_off));
> @@ -1011,10 +1027,28 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> return ret;
> }
>
> - for (i = 0; i < fentry->nr_links; i++)
> + if (fsession_cnt) {
> + /*
> + * Clear all the session cookies' values
> + * Clear the return value to make sure fentry always get 0
> + */
> + prepare_for_fsession_fentry(image, ctx, cookie_cnt, cookie_off, retval_off);
> + }
> +
> + cookie_ctx_off = (regs_off - cookie_off) / 8;
> +
> + for (i = 0; i < fentry->nr_links; i++) {
> + if (bpf_prog_calls_session_cookie(fentry->links[i])) {
> + u64 meta = func_meta | (cookie_ctx_off << BPF_TRAMP_COOKIE_INDEX_SHIFT);
> +
> + store_func_meta(image, ctx, meta, func_meta_off);
> + cookie_ctx_off--;
> + }
> +
> if (invoke_bpf_prog(image, ro_image, ctx, fentry->links[i], regs_off, retval_off,
> run_ctx_off, flags & BPF_TRAMP_F_RET_FENTRY_RET))
> return -EINVAL;
> + }
>
> if (fmod_ret->nr_links) {
> branches = kcalloc(fmod_ret->nr_links, sizeof(u32), GFP_KERNEL);
> @@ -1076,12 +1110,27 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
> image[branches[i]] = ppc_inst_val(branch_insn);
> }
>
> - for (i = 0; i < fexit->nr_links; i++)
> + /* set the "is_return" flag for fsession */
> + func_meta |= (1ULL << BPF_TRAMP_IS_RETURN_SHIFT);
> + if (fsession_cnt)
> + store_func_meta(image, ctx, func_meta, func_meta_off);
> +
> + cookie_ctx_off = (regs_off - cookie_off) / 8;
> +
> + for (i = 0; i < fexit->nr_links; i++) {
> + if (bpf_prog_calls_session_cookie(fexit->links[i])) {
> + u64 meta = func_meta | (cookie_ctx_off << BPF_TRAMP_COOKIE_INDEX_SHIFT);
> +
> + store_func_meta(image, ctx, meta, func_meta_off);
> + cookie_ctx_off--;
> + }
> +
> if (invoke_bpf_prog(image, ro_image, ctx, fexit->links[i], regs_off, retval_off,
> run_ctx_off, false)) {
> ret = -EINVAL;
> goto cleanup;
> }
> + }
>
> if (flags & BPF_TRAMP_F_CALL_ORIG) {
> if (ro_image) /* image is NULL for dummy pass */
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 6670d8c69ade..d9038c468af6 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -179,6 +179,31 @@ static int bpf_jit_stack_offsetof(struct codegen_context *ctx, int reg)
> BUG();
> }
>
> +void prepare_for_fsession_fentry(u32 *image, struct codegen_context *ctx, int cookie_cnt,
> + int cookie_off, int retval_off)
> +{
> + EMIT(PPC_RAW_LI(bpf_to_ppc(TMP_REG_1), 0));
> +
> + for (int i = 0; i < cookie_cnt; i++)
> + EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, cookie_off + 8 * i));
> + EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, retval_off));
> +}
> +
> +void store_func_meta(u32 *image, struct codegen_context *ctx,
> + u64 func_meta, int func_meta_off)
> +{
> + /*
> + * Store func_meta to stack at [R1 + func_meta_off] = func_meta
> + *
> + * func_meta :
> + * bit[63]: is_return flag
> + * byte[1]: cookie offset from ctx
> + * byte[0]: args count
> + */
> + PPC_LI64(bpf_to_ppc(TMP_REG_1), func_meta);
> + EMIT(PPC_RAW_STD(bpf_to_ppc(TMP_REG_1), _R1, func_meta_off));
> +}
> +
> void bpf_jit_realloc_regs(struct codegen_context *ctx)
> {
> }
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