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Mon, 5 Aug 2024 05:08:45 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5CF8F20040; Mon, 5 Aug 2024 05:08:43 +0000 (GMT) Received: from li-4f5ba44c-27d4-11b2-a85c-a08f5b49eada.in.ibm.com (unknown [9.109.204.94]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 5 Aug 2024 05:08:43 +0000 (GMT) From: Sourabh Jain To: bhe@redhat.com Subject: [PATCH] Document/kexec: Generalize crash hotplug description Date: Mon, 5 Aug 2024 10:38:29 +0530 Message-ID: <20240805050829.297171-1-sourabhjain@linux.ibm.com> X-Mailer: git-send-email 2.45.2 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: L8Nlt8mvubJ-cNSGhD1hDO3Zk7B6cMQV X-Proofpoint-ORIG-GUID: yt3EFoGssYFBIfPyYS6v6IoHcuXig4bQ X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-08-04_14,2024-08-02_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 mlxlogscore=999 phishscore=0 bulkscore=0 clxscore=1011 impostorscore=0 spamscore=0 mlxscore=0 priorityscore=1501 malwarescore=0 adultscore=0 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2407110000 definitions=main-2408050033 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Petr Tesarik , x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Sourabh Jain , linuxppc-dev@lists.ozlabs.org, Hari Bathini Errors-To: linuxppc-dev-bounces+incoming=patchwork.ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" Commit 79365026f869 ("crash: add a new kexec flag for hotplug support") generalizes the crash hotplug support to allow architectures to update multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. Therefore, update the relevant kernel documentation to reflect the same. No functional change. Cc: Petr Tesarik Cc: Hari Bathini Cc: kexec@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: linuxppc-dev@lists.ozlabs.org Cc: x86@kernel.org Signed-off-by: Sourabh Jain --- Discussion about the documentation update: https://lore.kernel.org/all/68d0328d-531a-4a2b-ab26-c97fd8a12e8b@linux.ibm.com/ --- .../ABI/testing/sysfs-devices-memory | 6 ++-- .../ABI/testing/sysfs-devices-system-cpu | 6 ++-- .../admin-guide/mm/memory-hotplug.rst | 5 ++-- Documentation/core-api/cpu_hotplug.rst | 10 ++++--- kernel/crash_core.c | 29 ++++++++++++------- 5 files changed, 33 insertions(+), 23 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory index a95e0f17c35a..421acc8e2c6b 100644 --- a/Documentation/ABI/testing/sysfs-devices-memory +++ b/Documentation/ABI/testing/sysfs-devices-memory @@ -115,6 +115,6 @@ What: /sys/devices/system/memory/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list Description: - (RO) indicates whether or not the kernel directly supports - modifying the crash elfcorehdr for memory hot un/plug and/or - on/offline changes. + (RO) indicates whether or not the kernel update of kexec + segments on memory hot un/plug and/or on/offline events, + avoiding the need to reload kdump kernel. diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 325873385b71..f4ada1cd2f96 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -703,9 +703,9 @@ What: /sys/devices/system/cpu/crash_hotplug Date: Aug 2023 Contact: Linux kernel mailing list Description: - (RO) indicates whether or not the kernel directly supports - modifying the crash elfcorehdr for CPU hot un/plug and/or - on/offline changes. + (RO) indicates whether or not the kernel update of kexec + segments on CPU hot un/plug and/or on/offline events, + avoiding the need to reload kdump kernel. What: /sys/devices/system/cpu/enabled Date: Nov 2022 diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index 098f14d83e99..cb2c080f400c 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -294,8 +294,9 @@ The following files are currently defined: ``crash_hotplug`` read-only: when changes to the system memory map occur due to hot un/plug of memory, this file contains '1' if the kernel updates the kdump capture kernel memory - map itself (via elfcorehdr), or '0' if userspace must update - the kdump capture kernel memory map. + map itself (via elfcorehdr and other relevant kexec + segments), or '0' if userspace must update the kdump + capture kernel memory map. Availability depends on the CONFIG_MEMORY_HOTPLUG kernel configuration option. diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst index dcb0e379e5e8..a21dbf261be7 100644 --- a/Documentation/core-api/cpu_hotplug.rst +++ b/Documentation/core-api/cpu_hotplug.rst @@ -737,8 +737,9 @@ can process the event further. When changes to the CPUs in the system occur, the sysfs file /sys/devices/system/cpu/crash_hotplug contains '1' if the kernel -updates the kdump capture kernel list of CPUs itself (via elfcorehdr), -or '0' if userspace must update the kdump capture kernel list of CPUs. +updates the kdump capture kernel list of CPUs itself (via elfcorehdr and +other relevant kexec segment), or '0' if userspace must update the kdump +capture kernel list of CPUs. The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration option. @@ -750,8 +751,9 @@ file can be used in a udev rule as follows: SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end" For a CPU hot un/plug event, if the architecture supports kernel updates -of the elfcorehdr (which contains the list of CPUs), then the rule skips -the unload-then-reload of the kdump capture kernel. +of the elfcorehdr (which contains the list of CPUs) and other relevant +kexec segments, then the rule skips the unload-then-reload of the kdump +capture kernel. Kernel Inline Documentations Reference ====================================== diff --git a/kernel/crash_core.c b/kernel/crash_core.c index 63cf89393c6e..64dad01e260b 100644 --- a/kernel/crash_core.c +++ b/kernel/crash_core.c @@ -520,18 +520,25 @@ int crash_check_hotplug_support(void) } /* - * To accurately reflect hot un/plug changes of cpu and memory resources - * (including onling and offlining of those resources), the elfcorehdr - * (which is passed to the crash kernel via the elfcorehdr= parameter) - * must be updated with the new list of CPUs and memories. + * To accurately reflect hot un/plug changes of CPU and Memory resources + * (including onling and offlining of those resources), the relevant + * kexec segments must be updated with latest CPU and Memory resources. * - * In order to make changes to elfcorehdr, two conditions are needed: - * First, the segment containing the elfcorehdr must be large enough - * to permit a growing number of resources; the elfcorehdr memory size - * is based on NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. - * Second, purgatory must explicitly exclude the elfcorehdr from the - * list of segments it checks (since the elfcorehdr changes and thus - * would require an update to purgatory itself to update the digest). + * Architectures must ensure two things for all segments that need + * updating during hotplug events: + * + * 1. Segments must be large enough to accommodate a growing number of + * resources. + * 2. Exclude the segments from SHA verification. + * + * For example, on most architectures, the elfcorehdr (which is passed + * to the crash kernel via the elfcorehdr= parameter) must include the + * new list of CPUs and memory. To make changes to the elfcorehdr, it + * should be large enough to permit a growing number of CPU and Memory + * resources. One can estimate the elfcorehdr memory size based on + * NR_CPUS_DEFAULT and CRASH_MAX_MEMORY_RANGES. The elfcorehdr is + * excluded from SHA verification by default if the architecture + * supports crash hotplug. */ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu, void *arg) {