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Thu, 02 Apr 2026 19:44:19 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay07.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 632JiFl651118480 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 2 Apr 2026 19:44:15 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ED7CB20043; Thu, 2 Apr 2026 19:44:14 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 74B9120040; Thu, 2 Apr 2026 19:44:10 +0000 (GMT) Received: from [9.39.19.166] (unknown [9.39.19.166]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 2 Apr 2026 19:44:10 +0000 (GMT) Message-ID: <3a26c38b-b408-46f4-93d8-0a829e04fb02@linux.ibm.com> Date: Fri, 3 Apr 2026 01:14:09 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] powerpc64/bpf: Add powerpc64 JIT support for timed may_goto To: Saket Kumar Bhaskar , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: sachinpb@linux.ibm.com, venkat88@linux.ibm.com, andrii@kernel.org, eddyz87@gmail.com, ast@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, chleroy@kernel.org, maddy@linux.ibm.com, mpe@ellerman.id.au, adubey@linux.ibm.com References: <20260402161026.289827-1-skb99@linux.ibm.com> Content-Language: en-US From: Hari Bathini In-Reply-To: <20260402161026.289827-1-skb99@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: W2_SXwwNJymNvLBKZ7DeCqwkIoAlexmE X-Authority-Analysis: v=2.4 cv=frzRpV4f c=1 sm=1 tr=0 ts=69cec714 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=sjD7eUQVPW1qbSBmM3gA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: 8TOzFD48rdEP0f6pDkt23awRtLgiN7Hg X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAyMDE3MyBTYWx0ZWRfX3ENea5jLjLyH 6qy4B4Pyqs3MP9TpN1D/RrG/fpWTu72tIxMJyS4bZzeP6SqsyMXmXGhgtR7epP9f41ArdBMXRbf hujG4SSXmWfH9O02qypKiKANYic5jn93lKZ0MKQV0dn/xEDTCsTxcpS+tAmRmEWdttV7BIY4Akr 9rRqKl+rJrZIhKNjj84dASMNgQ9ZVG6IRXhlxafKSFxdWkW2/rQa/p3pV72l43ac4J90W2BHebH PxjqnOgmse3uzT2lhSa8ZTGP6I+OjHOhXeQ3Rig7hlPNHrF2GySzknqLJ1SpJn8XKo1qniQD05R 2J4iPGREiWEyDPJxoc/gmrYDWbiQvsq3ld5X31h42tpVLu/9NklbhlbbJLR9G5YbOngijvcND37 USmzxkK3HbjvaIgVL9LwSVbwY8B1CO8JjwF7bFrwxmLWW1o2mk5niE40IMKtYn3Xxl4TFnK2WVT X9QPFR8XfEm4sHr7D4g== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-02_03,2026-04-02_05,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 priorityscore=1501 malwarescore=0 clxscore=1015 lowpriorityscore=0 bulkscore=0 adultscore=0 suspectscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604020173 On 02/04/26 9:40 pm, Saket Kumar Bhaskar wrote: > When verifier sees a timed may_goto instruction, it emits a call to > arch_bpf_timed_may_goto() with a stack offset in BPF_REG_AX > (powerpc64 R12) and expects the refreshed count value to be returned > in the same register. The verifier doesn't save or restore any registers > before emitting this call. > > arch_bpf_timed_may_goto() should act as a trampoline to call > bpf_check_timed_may_goto() with powerpc64 ELF ABI calling convention. > > To support this custom calling convention, implement > arch_bpf_timed_may_goto() in assembly and make sure BPF caller saved > registers are preserved, then call bpf_check_timed_may_goto with > the powerpc64 ABI calling convention where first argument and return > value both are in R3. Finally, move the result back into BPF_REG_AX(R12) > before returning. > > Also, introduce bpf_jit_emit_func_call() that computes the offset from > kernel_toc_addr(), validates that the target and emits the ADDIS/ADDI > sequence to load the function address before performing the indirect > branch via MTCTR/BCTRL. The existing code in bpf_jit_emit_func_call_rel() > is refactored to use this function. > Looks good to me. Acked-by: Hari Bathini > Signed-off-by: Saket Kumar Bhaskar > --- > This patch has been rebased on top of these 3 patches on powerpc-next in > the following sequence: > 1. https://lore.kernel.org/bpf/20260401103215.104438-1-adubey@linux.ibm.com/ > 2. https://lore.kernel.org/bpf/20260401141043.41513-1-adubey@linux.ibm.com/ > 3. https://lore.kernel.org/bpf/20260401152133.42544-1-adubey@linux.ibm.com/ > > Changes since v1: > - Compile bpf_timed_may_goto.o conditionally for PPC64. (Hari) > - Moved reladdr at the beginning of the function. (Hari) > - Added error check for bpf_jit_emit_func_call() in > bpf_jit_build_body(). (Hari) > - Save registers after 32 bytes as MIN_FRAME_SIZE is 32 bytes for > powerpc ABIv2. (Hari) > --- > arch/powerpc/net/Makefile | 4 ++ > arch/powerpc/net/bpf_jit_comp.c | 5 +++ > arch/powerpc/net/bpf_jit_comp64.c | 62 ++++++++++++++++++++++----- > arch/powerpc/net/bpf_timed_may_goto.S | 57 ++++++++++++++++++++++++ > 4 files changed, 117 insertions(+), 11 deletions(-) > create mode 100644 arch/powerpc/net/bpf_timed_may_goto.S > > diff --git a/arch/powerpc/net/Makefile b/arch/powerpc/net/Makefile > index 8e60af32e51e..87395d7e2672 100644 > --- a/arch/powerpc/net/Makefile > +++ b/arch/powerpc/net/Makefile > @@ -3,3 +3,7 @@ > # Arch-specific network modules > # > obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_jit_comp$(BITS).o > + > +ifdef CONFIG_PPC64 > ++obj-$(CONFIG_BPF_JIT) += bpf_timed_may_goto.o > +endif > diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c > index 50103b3794fb..9b2b456b0765 100644 > --- a/arch/powerpc/net/bpf_jit_comp.c > +++ b/arch/powerpc/net/bpf_jit_comp.c > @@ -537,6 +537,11 @@ bool bpf_jit_supports_subprog_tailcalls(void) > return IS_ENABLED(CONFIG_PPC64); > } > > +bool bpf_jit_supports_timed_may_goto(void) > +{ > + return IS_ENABLED(CONFIG_PPC64); > +} > + > bool bpf_jit_supports_kfunc_call(void) > { > return IS_ENABLED(CONFIG_PPC64); > diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c > index db364d9083e7..dab106cae22b 100644 > --- a/arch/powerpc/net/bpf_jit_comp64.c > +++ b/arch/powerpc/net/bpf_jit_comp64.c > @@ -451,10 +451,28 @@ void arch_bpf_stack_walk(bool (*consume_fn)(void *, u64, u64, u64), void *cookie > } > } > > +static int bpf_jit_emit_func_call(u32 *image, struct codegen_context *ctx, u64 func_addr, int reg) > +{ > + long reladdr = func_addr - kernel_toc_addr(); > + > + if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) { > + pr_err("eBPF: address of %ps out of range of kernel_toc.\n", (void *)func_addr); > + return -ERANGE; > + } > + > + EMIT(PPC_RAW_ADDIS(reg, _R2, PPC_HA(reladdr))); > + EMIT(PPC_RAW_ADDI(reg, reg, PPC_LO(reladdr))); > + EMIT(PPC_RAW_MTCTR(reg)); > + EMIT(PPC_RAW_BCTRL()); > + > + return 0; > +} > + > int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context *ctx, u64 func) > { > unsigned long func_addr = func ? ppc_function_entry((void *)func) : 0; > - long reladdr; > + long __maybe_unused reladdr; > + int ret; > > /* bpf to bpf call, func is not known in the initial pass. Emit 5 nops as a placeholder */ > if (!func) { > @@ -507,16 +525,9 @@ int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context * > EMIT(PPC_RAW_BCTRL()); > #else > if (core_kernel_text(func_addr)) { > - reladdr = func_addr - kernel_toc_addr(); > - if (reladdr > 0x7FFFFFFF || reladdr < -(0x80000000L)) { > - pr_err("eBPF: address of %ps out of range of kernel_toc.\n", (void *)func); > - return -ERANGE; > - } > - > - EMIT(PPC_RAW_ADDIS(_R12, _R2, PPC_HA(reladdr))); > - EMIT(PPC_RAW_ADDI(_R12, _R12, PPC_LO(reladdr))); > - EMIT(PPC_RAW_MTCTR(_R12)); > - EMIT(PPC_RAW_BCTRL()); > + ret = bpf_jit_emit_func_call(image, ctx, func_addr, _R12); > + if (ret) > + return ret; > } else { > if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1)) { > /* func points to the function descriptor */ > @@ -1755,6 +1766,35 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code > if (ret < 0) > return ret; > > + /* > + * Call to arch_bpf_timed_may_goto() is emitted by the > + * verifier and called with custom calling convention with > + * first argument and return value in BPF_REG_AX (_R12). > + * > + * The generic helper or bpf function call emission path > + * may use the same scratch register as BPF_REG_AX to > + * materialize the target address. This would clobber AX > + * and break timed may_goto semantics. > + * > + * Emit a minimal indirect call sequence here using a temp > + * register and skip the normal post-call return-value move. > + */ > + > + if (func_addr == (u64)arch_bpf_timed_may_goto) { > + ret = 0; > + if (!IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) > + ret = bpf_jit_emit_func_call(image, ctx, func_addr, > + tmp1_reg); > + > + if (ret || IS_ENABLED(CONFIG_PPC_KERNEL_PCREL)) { > + PPC_LI_ADDR(tmp1_reg, func_addr); > + EMIT(PPC_RAW_MTCTR(tmp1_reg)); > + EMIT(PPC_RAW_BCTRL()); > + } > + > + break; > + } > + > /* Take care of powerpc ABI requirements before kfunc call */ > if (insn[i].src_reg == BPF_PSEUDO_KFUNC_CALL) { > if (prepare_for_kfunc_call(fp, image, ctx, &insn[i])) > diff --git a/arch/powerpc/net/bpf_timed_may_goto.S b/arch/powerpc/net/bpf_timed_may_goto.S > new file mode 100644 > index 000000000000..6fd8b1c9f4ac > --- /dev/null > +++ b/arch/powerpc/net/bpf_timed_may_goto.S > @@ -0,0 +1,57 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* Copyright (c) 2025 IBM Corporation, Saket Kumar Bhaskar */ > + > +#include > +#include > + > +/* > + * arch_bpf_timed_may_goto() trampoline for powerpc64 > + * > + * Custom BPF convention (verifier/JIT): > + * - input: stack offset in BPF_REG_AX (r12) > + * - output: updated count in BPF_REG_AX (r12) > + * > + * Call bpf_check_timed_may_goto(ptr) with normal powerpc64 ABI: > + * - r3 = ptr, return in r3 > + * > + * Preserve BPF regs R0-R5 (mapping: r8, r3-r7). > + */ > + > +SYM_FUNC_START(arch_bpf_timed_may_goto) > + /* Prologue: save LR, allocate frame */ > + mflr r0 > + std r0, 16(r1) > + stdu r1, -112(r1) > + > + /* Save BPF registers R0 - R5 (r8, r3-r7) */ > + std r3, 32(r1) > + std r4, 40(r1) > + std r5, 48(r1) > + std r6, 56(r1) > + std r7, 64(r1) > + std r8, 72(r1) > + > + /* > + * r3 = BPF_REG_FP + BPF_REG_AX > + * BPF_REG_FP is r31; BPF_REG_AX is r12 (stack offset in bytes). > + */ > + add r3, r31, r12 > + bl bpf_check_timed_may_goto > + > + /* Put return value back into AX */ > + mr r12, r3 > + > + /* Restore BPF registers R0 - R5 (r8, r3-r7) */ > + ld r3, 32(r1) > + ld r4, 40(r1) > + ld r5, 48(r1) > + ld r6, 56(r1) > + ld r7, 64(r1) > + ld r8, 72(r1) > + > + /* Epilogue: pop frame, restore LR, return */ > + addi r1, r1, 112 > + ld r0, 16(r1) > + mtlr r0 > + blr > +SYM_FUNC_END(arch_bpf_timed_may_goto)