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Message-ID: <20260105105212.136645-4-adubey@linux.ibm.com>
Date: Mon, 5 Jan 2026 16:22:09 +0530
From: adubey@...ux.ibm.com
To: bpf@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: hbathini@...ux.ibm.com, sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com,
andrii@...nel.org, eddyz87@...il.com, mykolal@...com, ast@...nel.org,
daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org,
yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
christophe.leroy@...roup.eu, naveen@...nel.org, maddy@...ux.ibm.com,
mpe@...erman.id.au, npiggin@...il.com, memxor@...il.com,
iii@...ux.ibm.com, shuah@...nel.org,
Abhishek Dubey <adubey@...ux.ibm.com>
Subject: [PATCH 3/6] powerpc/bpf: use BPF_PPC_STACK_SAVE to spill trampoline NVRs
From: Abhishek Dubey <adubey@...ux.ibm.com>
In the previous patch, we introduced BPF_PPC_STACK_SAVE
into the trampoline frame to make its layout consistent
with a conventional stack frame.
The trampoline JIT currently uses NVRs R25 and R26 and
allocates dedicated stack slots to save them. This
dedicated space can be eliminated by reusing the
BPF_PPC_STACK_SAVE area instead, reducing overall stack
footprint.
The BPF_PPC_STACK_SAVE area corresponds to the register
range R26–R31. By remapping registers in the trampoline
JIT code (R25 → R26 and R26 → R27), we can spill these
registers into the existing save area and utilize the stack
more efficiently.
Signed-off-by: Abhishek Dubey <adubey@...ux.ibm.com>
---
arch/powerpc/net/bpf_jit_comp.c | 27 +++++++++++----------------
1 file changed, 11 insertions(+), 16 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 4aaa0a287a45..b09d294084d4 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -512,7 +512,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
/* __bpf_prog_enter(p, &bpf_tramp_run_ctx) */
PPC_LI_ADDR(_R3, p);
- EMIT(PPC_RAW_MR(_R25, _R3));
+ EMIT(PPC_RAW_MR(_R26, _R3));
EMIT(PPC_RAW_ADDI(_R4, _R1, run_ctx_off));
ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
(unsigned long)bpf_trampoline_enter(p));
@@ -520,7 +520,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
return ret;
/* Remember prog start time returned by __bpf_prog_enter */
- EMIT(PPC_RAW_MR(_R26, _R3));
+ EMIT(PPC_RAW_MR(_R27, _R3));
/*
* if (__bpf_prog_enter(p) == 0)
@@ -543,7 +543,7 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
image[ctx->idx] = ppc_inst_val(branch_insn);
ctx->idx++;
} else {
- EMIT(PPC_RAW_LL(_R12, _R25, offsetof(struct bpf_prog, bpf_func)));
+ EMIT(PPC_RAW_LL(_R12, _R26, offsetof(struct bpf_prog, bpf_func)));
EMIT(PPC_RAW_MTCTR(_R12));
EMIT(PPC_RAW_BCTRL());
}
@@ -560,8 +560,8 @@ static int invoke_bpf_prog(u32 *image, u32 *ro_image, struct codegen_context *ct
}
/* __bpf_prog_exit(p, start_time, &bpf_tramp_run_ctx) */
- EMIT(PPC_RAW_MR(_R3, _R25));
- EMIT(PPC_RAW_MR(_R4, _R26));
+ EMIT(PPC_RAW_MR(_R3, _R26));
+ EMIT(PPC_RAW_MR(_R4, _R27));
EMIT(PPC_RAW_ADDI(_R5, _R1, run_ctx_off));
ret = bpf_jit_emit_func_call_rel(image, ro_image, ctx,
(unsigned long)bpf_trampoline_exit(p));
@@ -748,12 +748,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
* [ r0 save (32-bit) ] |
* dummy frame for unwind [ back chain 1 ] --
* [ padding ] align stack frame
- * [ r26..r31 ] nvr save : BPF_PPC_STACK_SAVE
+ * nvr_off [ r26..r31 ] nvr save : BPF_PPC_STACK_SAVE
* [ tail_call_info ] non optional - 64-bit powerpc
* r4_off [ r4 (tailcallcnt) ] optional - 32-bit powerpc
* alt_lr_off [ real lr (ool stub)] optional - actual lr
- * [ r26 ]
- * nvr_off [ r25 ] nvr save area
* retval_off [ return value ]
* [ reg argN ]
* [ ... ]
@@ -811,10 +809,6 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
if (save_ret)
bpf_frame_size += SZL;
- /* Room for nvr save area */
- nvr_off = bpf_frame_size;
- bpf_frame_size += 2 * SZL;
-
/* Optional save area for actual LR in case of ool ftrace */
if (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE)) {
alt_lr_off = bpf_frame_size;
@@ -834,6 +828,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
bpf_frame_size += SZL;
/* Room for nvr save area */
+ nvr_off = bpf_frame_size;
bpf_frame_size += BPF_PPC_STACK_SAVE;
/* Padding to align stack frame, if any */
@@ -897,8 +892,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
EMIT(PPC_RAW_STL(_R3, _R1, nregs_off));
/* Save nv regs */
- EMIT(PPC_RAW_STL(_R25, _R1, nvr_off));
- EMIT(PPC_RAW_STL(_R26, _R1, nvr_off + SZL));
+ EMIT(PPC_RAW_STL(_R26, _R1, nvr_off));
+ EMIT(PPC_RAW_STL(_R27, _R1, nvr_off + SZL));
if (flags & BPF_TRAMP_F_CALL_ORIG) {
PPC_LI_ADDR(_R3, (unsigned long)im);
@@ -999,8 +994,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
EMIT(PPC_RAW_LL(_R3, _R1, retval_off));
/* Restore nv regs */
- EMIT(PPC_RAW_LL(_R26, _R1, nvr_off + SZL));
- EMIT(PPC_RAW_LL(_R25, _R1, nvr_off));
+ EMIT(PPC_RAW_LL(_R27, _R1, nvr_off + SZL));
+ EMIT(PPC_RAW_LL(_R26, _R1, nvr_off));
/* Epilogue */
if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && !IS_ENABLED(CONFIG_PPC_KERNEL_PCREL))
--
2.48.1
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