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Thu, 02 Apr 2026 13:16:02 +0000 Received: from smtpav04.fra02v.mail.ibm.com (smtpav04.fra02v.mail.ibm.com [10.20.54.103]) by smtprelay01.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 632DFwmS54723026 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 2 Apr 2026 13:15:58 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2CB2F20073; Thu, 2 Apr 2026 13:15:58 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5D5DE2006C; Thu, 2 Apr 2026 13:15:54 +0000 (GMT) Received: from [9.124.211.83] (unknown [9.124.211.83]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 2 Apr 2026 13:15:54 +0000 (GMT) Message-ID: Date: Thu, 2 Apr 2026 18:45:53 +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] 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: <20260402054249.28801-1-skb99@linux.ibm.com> Content-Language: en-US From: Hari Bathini In-Reply-To: <20260402054249.28801-1-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: Zm4SQeeocor-YrMLtjR7rk28-DXVJAs8 X-Authority-Analysis: v=2.4 cv=frzRpV4f c=1 sm=1 tr=0 ts=69ce6c13 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=sjD7eUQVPW1qbSBmM3gA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: 8JgscKiQBGn9pYynFAGYJa9FQLJ7T3-4 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAyMDExNiBTYWx0ZWRfX9Hek6HY48SI5 05g4BuM1uw0Vf8NcCs8jZpawdT+1K4+CiI38uBsLc8FNUyBbZfwKH26K5X/FDMAjDwDkJcFxlON 2D86zoZX90MhkAu+QNldZD8nmO9H0uek0U7LPHBe3XZKpzd7Rtf0tw06Ei7KKdgj0Ui9kQI/S0T mosXXiuSTczfNQHNupEwMW2zzuj12t9yiCEd9RTKZsJJolEru+mFt7lK44b+QDcEUuENtZfo+gU oXSrQEOBTa7MOg6T/mBpkjE3OYegwsbz5jM2HyNgWThvgmPaCv6SrLe89Cz2ciSsS1H6f7VgmpD Sb4MT3uDoLZrNzkRFbWNJmb/6aQUEUWqcVWs0/9K8y+Vdxdbe7gmOL3B+Q+R00rb7bVag3tj4rG 2Ijx8tjpEhRAs3Xjc02N39zkT5v7J6UPKa7C8BoTkYXGYxnd/WfP2rAtCNe2t4O7z9jKq8B3f4x YczbcbQ9bD/ZnIFLVAA== 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_01,2026-04-02_02,2025-10-01_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-2604020116 On 02/04/26 11:12 am, 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. > > Signed-off-by: Saket Kumar Bhaskar > --- > arch/powerpc/net/Makefile | 2 +- > arch/powerpc/net/bpf_jit_comp.c | 5 +++ > arch/powerpc/net/bpf_jit_comp64.c | 59 ++++++++++++++++++++++----- > arch/powerpc/net/bpf_timed_may_goto.S | 57 ++++++++++++++++++++++++++ > 4 files changed, 111 insertions(+), 12 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..204fc57ac56e 100644 > --- a/arch/powerpc/net/Makefile > +++ b/arch/powerpc/net/Makefile > @@ -2,4 +2,4 @@ > # > # Arch-specific network modules > # > -obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_jit_comp$(BITS).o > +obj-$(CONFIG_BPF_JIT) += bpf_jit_comp.o bpf_jit_comp$(BITS).o bpf_timed_may_goto.o As this is currently only enabled for CONFIG_PPC64, bpf_timed_may_goto.o should be compiled conditionally for PPC64: 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..d39241444cd9 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; > + > + reladdr = func_addr - kernel_toc_addr(); 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; > + int ret; > > /* bpf to bpf call, func is not known in the initial pass. Emit 5 nops as a placeholder */ > if (!func) { > @@ -469,6 +487,7 @@ int bpf_jit_emit_func_call_rel(u32 *image, u32 *fimage, struct codegen_context * > } > > #ifdef CONFIG_PPC_KERNEL_PCREL > + long reladdr; While this works with modern C standard, I would be conservative and let this be at the start of the function itself.. > reladdr = func_addr - local_paca->kernelbase; > > /* > @@ -507,16 +526,9 @@ 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 +1767,31 @@ 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) { > +#ifdef CONFIG_PPC_KERNEL_PCREL > + PPC_LI_ADDR(tmp1_reg, func_addr); > + EMIT(PPC_RAW_MTCTR(tmp1_reg)); > + EMIT(PPC_RAW_BCTRL()); > +#else > + bpf_jit_emit_func_call(image, ctx, func_addr, tmp1_reg); The error check is missing for the above function.. Actually, how about: 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()); } > +#endif > + 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..0b9afe3cfa1f > --- /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, 24(r1) May not matter much for this handwritten function but can we use 32 and on instead, as 32 is the MIN_FRAME_SIZE on ABIv2? > + std r4, 32(r1) > + std r5, 40(r1) > + std r6, 48(r1) > + std r7, 56(r1) > + std r8, 64(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, 24(r1) > + ld r4, 32(r1) > + ld r5, 40(r1) > + ld r6, 48(r1) > + ld r7, 56(r1) > + ld r8, 64(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) - Hari