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Mon, 16 Feb 2026 08:36:30 +0000 Received: from smtpav06.fra02v.mail.ibm.com (smtpav06.fra02v.mail.ibm.com [10.20.54.105]) by smtprelay04.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 61G8aPgo20840962 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 16 Feb 2026 08:36:26 GMT Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DDF9C2004D; Mon, 16 Feb 2026 08:36:25 +0000 (GMT) Received: from smtpav06.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8B62920049; Mon, 16 Feb 2026 08:36:23 +0000 (GMT) Received: from [9.78.106.17] (unknown [9.78.106.17]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 16 Feb 2026 08:36:23 +0000 (GMT) Message-ID: <87b92f46-8b05-4061-949c-4c15afc55d29@linux.ibm.com> Date: Mon, 16 Feb 2026 14:06:22 +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 5/5] powerpc64/bpf: fix handling of BPF stack in exception callback To: bot+bpf-ci@kernel.org, linuxppc-dev@lists.ozlabs.org Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, skb99@linux.ibm.com, adubey@linux.ibm.com, martin.lau@kernel.org, eddyz87@gmail.com, yonghong.song@linux.dev, clm@meta.com, ihor.solodrai@linux.dev References: <20260216065639.1750181-6-hbathini@linux.ibm.com> <5f92f12e74b1c8d6fa54ec72590d5087a3c8b7ac2d7302309936db6bd196f5cc@mail.kernel.org> Content-Language: en-US From: Hari Bathini In-Reply-To: <5f92f12e74b1c8d6fa54ec72590d5087a3c8b7ac2d7302309936db6bd196f5cc@mail.kernel.org> 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-Spam-Details-Enc: AW1haW4tMjYwMjE2MDA2NyBTYWx0ZWRfX77AkWTr2afRm gi64dMH77NNwHAYLooc7bGz9wmIR7SjtQhexbNyhQc5qgkJOX0Nh0NTXN2gNFjk6lucImhg/Vpx 7f81RRrAeILeAOu06Z9dV07UXN7asbf4S476OQx2Dwl0yKWwxo8eAsypCjlLCbmgHNThYW4euR4 7rFs1LWUgrBs46mp/jVevaoWIXgtWs3F44CT5noZjelmNGysL2K3juga+7LynVu4c9kBdWX0f47 XwfjcPVT5VdwXKPvxCDMy10UgpxR583FYzbRTMxjdAN96Oxa8Xbvw65t/CitQGrfj9SyuO/NYH5 vz1aGafiunUmBkeBXEs+s6+ziwt5Vagrxhp6cBm44zaZpW/fKxGF/RslP+KGtAkhKEazclblpzE 5Q23D9y+qMsnFgZvyipqFuN6SV5kPn6XX9jKhUc0aqeiYHPo8AqiBeIZGRNBh5HGxt4/1rLbFsu mcjzuJ7DbQE9ke2uhsA== X-Proofpoint-ORIG-GUID: dUEtbjr8eV1VnIqXfqevM8ijjJfpVQhl X-Proofpoint-GUID: mCspMg7hfWqjXDzVlr07iz_OuCWjX2Wp X-Authority-Analysis: v=2.4 cv=M7hA6iws c=1 sm=1 tr=0 ts=6992d70f cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=Mpw57Om8IfrbqaoTuvik:22 a=GgsMoib0sEa3-_RKJdDe:22 a=VwQbUJbxAAAA:8 a=vP-F963z1u4rLPN7kLoA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-16_03,2026-02-16_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 lowpriorityscore=0 clxscore=1015 phishscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2601150000 definitions=main-2602160067 On 16/02/26 1:10 pm, bot+bpf-ci@kernel.org wrote: >> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c >> --- a/arch/powerpc/net/bpf_jit_comp64.c >> +++ b/arch/powerpc/net/bpf_jit_comp64.c > > [ ... ] > >> @@ -287,6 +285,22 @@ >> * program(main prog) as third arg >> */ >> EMIT(PPC_RAW_MR(_R1, _R5)); >> + /* >> + * Exception callback reuses the stack frame of exception boundary. >> + * But BPF stack depth of exception callback and exception boundary >> + * don't have to be same. If BPF stack depth is different, adjust the >> + * stack frame size considering BPF stack depth of exception callback. >> + * The non-volatile register save area remains unchanged. These non- >> + * volatile registers are restored in exception callback's epilogue. >> + */ >> + EMIT(PPC_RAW_LD(bpf_to_ppc(TMP_REG_1), _R5, 0)); >> + EMIT(PPC_RAW_SUB(bpf_to_ppc(TMP_REG_2), _R1, bpf_to_ppc(TMP_REG_1))); > > Are the operands to PPC_RAW_SUB reversed here? At this point R1 holds > boundary_sp (set by the MR above) and TMP_REG_1 holds prev_sp (loaded > from [R5+0]). Since the stack grows downward, boundary_sp < prev_sp. > > PPC_RAW_SUB(d, a, b) computes d = a - b, confirmed by how BPF_SUB is > emitted in bpf_jit_build_body(): > > case BPF_ALU64 | BPF_SUB | BPF_X: /* dst -= src */ > EMIT(PPC_RAW_SUB(dst_reg, dst_reg, src_reg)); That was a good catch. "subf Rx,Ry,Rz" vs "sub Rx,Rz,Ry" distinction on how the operation is interpreted. Will respin. - Hari