linux-kernel - [PATCH v3 3/6] powerpc64/bpf: Avoid tailcall restore from trampoline

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Message-ID: <20260122165716.10508-4-adubey@linux.ibm.com>
Date: Thu, 22 Jan 2026 22:27:13 +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 v3 3/6] powerpc64/bpf: Avoid tailcall restore from trampoline

From: Abhishek Dubey <adubey@...ux.ibm.com>

Back propagation of tailcall count is no longer needed for
powerpc64 due to use of reference, which updates the tailcall
count in the tail_call_info field in the frame of the main
program only.

Back propagation is still required for 32-bit powerpc.

Signed-off-by: Abhishek Dubey <adubey@...ux.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index f3ee031edc26..9a8236d161ef 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -662,16 +662,11 @@ static void bpf_trampoline_setup_tail_call_info(u32 *image, struct codegen_conte
 static void bpf_trampoline_restore_tail_call_cnt(u32 *image, struct codegen_context *ctx,
 						 int func_frame_offset, int r4_off)
 {
-	if (IS_ENABLED(CONFIG_PPC64)) {
-		/* See bpf_jit_stack_tailcallcnt() */
-		int tailcallcnt_offset = 7 * 8;
-
-		EMIT(PPC_RAW_LL(_R3, _R1, -tailcallcnt_offset));
-		EMIT(PPC_RAW_STL(_R3, _R1, func_frame_offset - tailcallcnt_offset));
-	} else {
-		/* See bpf_jit_stack_offsetof() and BPF_PPC_TC */
-		EMIT(PPC_RAW_STL(_R4, _R1, r4_off));
-	}
+	/*
+	 * Restore tailcall for 32-bit ppc.
+	 * See bpf_jit_stack_offsetof() and BPF_PPC_TC
+	 */
+	EMIT(PPC_RAW_STL(_R4, _R1, r4_off));
 }
 
 static void bpf_trampoline_save_args(u32 *image, struct codegen_context *ctx, int func_frame_offset,
-- 
2.48.1