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Wed, 03 Dec 2025 20:07:20 -0800 (PST) Received: from hu-pkondeti-hyd.qualcomm.com ([202.46.22.19]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7e29f2ecf6fsm527934b3a.11.2025.12.03.20.07.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Dec 2025 20:07:20 -0800 (PST) Date: Thu, 4 Dec 2025 09:37:15 +0530 From: Pavan Kondeti To: Catalin Marinas , Will Deacon , Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, rsalveti@oss.qualcomm.com Subject: Alternative to arm64.nopauth cmdline for disabling Pointer Authentication Message-ID: <3fcf6614-ee83-4a06-9024-83573b2e642e@quicinc.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Proofpoint-ORIG-GUID: BjR9078H5Rr2brUCupJOjt8ydg-pVyLC X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjA0MDAzMCBTYWx0ZWRfX4Fwnq/T3ew3S MvZQ/K3QVoZ8gjEB+iu6GwtIAXbxBcRnJq0npTkYLY5DvM4Wt/QLxpY4zg6nMEtPWb0JS1CYWNA 1mni/l9PL2wUiyE114JLrdpRJyxMj/TrP5mfbGBIpwc9mE6kRKsdX7x5jpwn+v4urLl/l9mvfIM y1mdEwOVANbWVC6P44han9giPat7O8rxGxyc3R9YjSN3KXhYo4KnxBWek2V/3nKEphE50ii8pPo xXp85E/MzBnJWX0outkWxuot29a7n4GrGj9MxdgkWvHzIkGE3BDtDSrX7tWFEcMLxHHaHKOIjBG 01/sXE8SzyRhf6pynXzafAgd3sYS5hZXujeU1Qx3Z3vFRXfc+e6r6St8RzsMq5TvnFaCwEup+6l usEXkSE6A/AzEOvL7O6HSymM9OLhBg== X-Proofpoint-GUID: BjR9078H5Rr2brUCupJOjt8ydg-pVyLC X-Authority-Analysis: v=2.4 cv=ZqDg6t7G c=1 sm=1 tr=0 ts=693108f9 cx=c_pps a=0uOsjrqzRL749jD1oC5vDA==:117 a=fChuTYTh2wq5r3m49p7fHw==:17 a=kj9zAlcOel0A:10 a=wP3pNCr1ah4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=NEAV23lmAAAA:8 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=Yi-RDYHqs8T9QeDE7fwA:9 a=CjuIK1q_8ugA:10 a=mQ_c8vxmzFEMiUWkPHU9:22 a=a-qgeE7W1pNrGK8U0ZQC:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-04_01,2025-12-03_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 impostorscore=0 lowpriorityscore=0 suspectscore=0 priorityscore=1501 spamscore=0 bulkscore=0 adultscore=0 phishscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2512040030 Hi The pointer authentication feature (PAuth) is only supported on 0-3 CPUs but it is not supported on 4-7 CPUS on QCS8300. The ARM64 cpufeature discovery code expects late CPUs to have this feature if boot CPU feature has it since PAuth is enabled early. When a conflict like this is detected, the late CPUs are not allowed to boot. It is expected that system will continue to be functional with CPUs with Pauth feature supported and enabled. This is not a desired behavior in production. We started seeing this problem when Linux is booted in EL2. When Linux is running under Gunyah (Type-1 hypervisor), Pointer Authentication feature is hidden from EL1 via HCR_EL2.TID3. arm64.nopauth can be passed on kernel cmdline to disable the feature in kernel so that all all CPUs can boot on QCS8300. I am told maintaining a custom kernel commandline per SoC in a Generic OS distribution is not recommended and asked to discuss the problem with the comunity [1] This patch [2] from Catalin adds a devicetree property under memory {} to disable MTE. I believe this work predates the id-reg override mechanism. However, this made me think if workarounds like this can be detected via devicetree, for example a property under cpu { } node. Given that what we put in `chosen { bootargs="" }` kernel under respective SoC devicetree can be overridden by bootloader, should we have a **sticky** cmdline to specify critical workarounds like this? This would be more generic than introducing any new parameters. Looking for your inputs on this. Thanks, Pavan [1] https://github.com/qualcomm-linux/meta-qcom/issues/1277 [2] https://lore.kernel.org/linux-arm-kernel/20200515171612.1020-24-catalin.marinas@arm.com/