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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35fd3230ee5sm1292243a91.15.2026.04.15.01.45.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 15 Apr 2026 01:45:48 -0700 (PDT) Message-ID: Date: Wed, 15 Apr 2026 16:45:44 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 3/9] coresight: etm4x: fix leaked trace id To: Leo Yan , Yeoreum Yun Cc: coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, suzuki.poulose@arm.com, mike.leach@arm.com, james.clark@linaro.org, alexander.shishkin@linux.intel.com References: <20260413142003.3549310-1-yeoreum.yun@arm.com> <20260413142003.3549310-4-yeoreum.yun@arm.com> <20260414163221.GG356832@e132581.arm.com> <81fdef8a-a60e-4d29-948d-c4a07e23dad9@oss.qualcomm.com> <20260415072933.GH356832@e132581.arm.com> <20260415083224.GJ356832@e132581.arm.com> Content-Language: en-US From: Jie Gan In-Reply-To: <20260415083224.GJ356832@e132581.arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDE1MDA3OCBTYWx0ZWRfX19ZrCNWjRATr Lmh5XHhI3m2h4A7PJp1J94o0Wramkyo6N9svCSul+in9I6bWFkQYyDFGEuOsvA9y3XqQXeKgwcr CAull5kITlm8Owm8N0XLwV3aoIwDDNjGOWdwKHdLh6aLSeM8FRRhsGdP3KqW/JVYNJrovEqurSe WNYYXbV7BWi6+v0PwIDiyNDA1HwOFqHtedTJdKVNCBJvPbYDLHCjQXI4pIQza4X42/xjbji42wS A/jYwrZhqGfRUyvFjuU+7JI9NBhBNUomyvYyG7MxlW9x8vn4K7YFZBkdilf81hqfTKbr4+Cjtww jJiWLIxd5lkdiLtKqtjagkn+jPIh/z//izLsEU6OmlqW3WNrbgduW0gikju8Sh5uQlSEQy78RK7 uOyle8XkDJVAJcUfdg0pXgf5umNFYeDx+fNndc/4w0VgwvFo7mxsfjc8MZItsAVBObe6Y4uoizT l5EgAYwLIuHGPh/RnBw== X-Proofpoint-ORIG-GUID: VPB2S2_NeKkSGQGV8EJgH1T-NLrEM2_m X-Authority-Analysis: v=2.4 cv=ZIfnX37b c=1 sm=1 tr=0 ts=69df503e cx=c_pps a=vVfyC5vLCtgYJKYeQD43oA==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=rJkE3RaqiGZ5pbrm-msn:22 a=6anqEM3ORI0LkIs7FgEA:9 a=QEXdDO2ut3YA:10 a=rl5im9kqc5Lf4LNbBjHf:22 X-Proofpoint-GUID: VPB2S2_NeKkSGQGV8EJgH1T-NLrEM2_m 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=2026-04-14_04,2026-04-13_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 suspectscore=0 lowpriorityscore=0 spamscore=0 bulkscore=0 phishscore=0 clxscore=1015 malwarescore=0 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604070000 definitions=main-2604150078 On 4/15/2026 4:32 PM, Leo Yan wrote: > On Wed, Apr 15, 2026 at 09:01:09AM +0100, Yeoreum Yun wrote: > > [...] > >>>> What I am thinking is as SoCs continue to grow more complex with an >>>> increasing number of subsystems, trace IDs may be exhausted in the near >>>> future. (that's why we have dynamic trace ID allocation/release). >>> >>> Thanks for the input. >>> >>> I am wandering if we can use "dev->devt" as the trace ID. A device's >>> major/minor number is unique in kernel and dev_t is defined as u32: >>> >>> typedef u32 __kernel_dev_t; >>> >>> And we can consolidate this for both SYSFS and PERF modes. >>> >> >> When I see the CORESIGHT_TRACE_ID_MAX: >> >> /* architecturally we have 128 IDs some of which are reserved */ >> #define CORESIGHT_TRACE_IDS_MAX 128 >> >> I think this came from the hardware restriction for number of TRACE_IDs. >> In this case, clamping the device_id to trace_id seems more complex and >> reduce some performance perspective. > > Sigh, my stupid. Please ignore my previous comment, let us first fix > ID leak issue. > > Given Jie's comment on the use-out issue, it is valid for me especially > if a system have many dummy tracers. We can defer to refactor it > later (e.g., use separate ranges for hardware and dummy tracers). > > thanks for correction! Just share some info: With my memory, The ARM AMBA ATB Protocol Specification defined a 7-bit width field for the trace ID, that's where the 128 comes from. (in each frame, we also have 7-bit field for containing the trace ID) Thanks, Jie