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Wed, 19 Aug 2026 03:12:15 -0700 (PDT) Received: from localhost ([2400:ac40:62f:3ae5:75e6:e4f4:4401:4289]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3957f96ca41sm2089556a91.4.2026.08.19.03.12.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Aug 2026 03:12:15 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Wed, 19 Aug 2026 18:09:52 +0800 To: Sourabh Jain Cc: kexec@lists.infradead.org, Andrew Morton , Baoquan He , Dave Young , Pratyush Yadav , Mike Rapoport , Pasha Tatashin , Jonathan Corbet , Shuah Khan , Coiby Xu , "open list:DOCUMENTATION" , open list Subject: Re: [PATCH v3 09/10] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported Message-ID: References: <20260729033654.311541-1-coiby.xu@gmail.com> <20260729033654.311541-10-coiby.xu@gmail.com> <96a78b35-94f7-4b63-97d3-d0841681e2b4@linux.ibm.com> <8d857834-e014-44d9-a112-d7fc8482d7c3@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8d857834-e014-44d9-a112-d7fc8482d7c3@linux.ibm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260819_031217_733729_197384CE X-CRM114-Status: GOOD ( 18.94 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On Sun, Aug 09, 2026 at 05:36:50PM +0530, Sourabh Jain wrote: > > >On 06/08/26 11:03, Coiby Xu wrote: >>On Wed, Aug 05, 2026 at 05:39:28PM +0530, Sourabh Jain wrote: >>> >>> >>>On 29/07/26 09:06, Coiby Xu wrote: >>>>If crash hotplug is supported, dm-crypt keys saved to reserved memory >>>>will be taken care of automatically. Thus it doesn't make sense to use >>>>configfs/crash_dm_crypt_key/reuse. Reserving image->dm_crypt_keys_addr >>>>is also unnecessary. Currently x86_64 and ppc64le have implemented >>>>crash hotplug feature. >>>> >>>>Also update the doc accordingly. Note two doc issues are fixed as well. >>>> >>>>Fixes: 9ebfa8dcaea7 ("crash_dump: reuse saved dm crypt keys for >>>>CPU/memory hot-plugging") >>>>Signed-off-by: Coiby Xu >>>>--- >>>> Documentation/admin-guide/kdump/kdump.rst | 16 ++++++++++------ >>>> kernel/crash_dump_dm_crypt.c              | 23 ++++++++++++++++++++--- >>>> 2 files changed, 30 insertions(+), 9 deletions(-) >>>> >>>>diff --git a/Documentation/admin-guide/kdump/kdump.rst >>>>b/Documentation/admin-guide/kdump/kdump.rst >>>>index 7587caadbae1..0bf2eb100a05 100644 >>>>--- a/Documentation/admin-guide/kdump/kdump.rst >>>>+++ b/Documentation/admin-guide/kdump/kdump.rst >>>>@@ -577,9 +577,10 @@ with /sys/kernel/config/crash_dm_crypt_keys >>>>for setup, >>>> 1. Tell the first kernel what logon keys are needed to unlock >>>>the disk volumes, >>>>     # Add key #1 >>>>-    mkdir /sys/kernel/config/crash_dm_crypt_keys/7d26b7b4-e342-4d2d-b660-7426b0996720 >>>>+    VOL1_UUID=7d26b7b4-e342-4d2d-b660-7426b0996720 >>>>+    mkdir /sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID >>>>     # Add key #1's description >>>>-    echo cryptsetup:7d26b7b4-e342-4d2d-b660-7426b0996720 > >>>>/sys/kernel/config/crash_dm_crypt_keys/description >>>>+    echo cryptsetup:$VOL1_UUID > >>>>/sys/kernel/config/crash_dm_crypt_keys/$VOL1_UUID/description >>>>     # how many keys do we have now? >>>>     cat /sys/kernel/config/crash_dm_crypt_keys/count >>>>@@ -591,15 +592,18 @@ with >>>>/sys/kernel/config/crash_dm_crypt_keys for setup, >>>>     cat /sys/kernel/config/crash_dm_crypt_keys/count >>>>     2 >>>>-    # To support CPU/memory hot-plugging, reuse keys already >>>>saved to reserved >>>>-    # memory >>>>-    echo true > /sys/kernel/config/crash_dm_crypt_key/reuse >>>>- >>>> 2. Load the dump-capture kernel >>>> 3. After the dump-capture kerne get booted, restore the keys to >>>>user keyring >>>>    echo yes > /sys/kernel/crash_dm_crypt_keys/restore >>>>+For CPU/memory hot-plugging, you can reuse keys already saved >>>>to reserved >>>>+memory before reloading the kdump image, >>>>+    echo true > /sys/kernel/config/crash_dm_crypt_keys/reuse >>>>+ >>>>+Note if crash hotplug is supported, this API is totally >>>>unnecessary thus will >>>>+be disabled automatically. >>>>+ >>>> Contact >>>> ======= >>>>diff --git a/kernel/crash_dump_dm_crypt.c >>>>b/kernel/crash_dump_dm_crypt.c >>>>index b5b78656cf06..46d6b31c3ca4 100644 >>>>--- a/kernel/crash_dump_dm_crypt.c >>>>+++ b/kernel/crash_dump_dm_crypt.c >>>>@@ -310,6 +310,15 @@ static ssize_t >>>>config_keys_reuse_show(struct config_item *item, char *page) >>>>     return sysfs_emit(page, "%d\n", is_dm_key_reused); >>>> } >>>>+static bool crash_hotplug_support(struct kimage *image) >>>>+{ >>>>+#ifdef CONFIG_CRASH_HOTPLUG >>>>+    return image->hotplug_support; >>> >>>I don't think it is good idea to access kexec_crash_image >>>properties without >>>holding the kexec lock. >> >>Thanks for raising the concern! Let's discuss this issue in [PATCH >>v3 03/10]. >> >>> >>>Also, would it make sense to move this API somewhere else? >> >>Can you help me understand why to move this API? Is it because using >>ifdef in .c file is discouraged? > >This API is used to verify crash hotplug support, which is not >directly related to crash_dm_crypt_keys. >It also seems to be generally useful. > >- Sourabh Jain Thanks for the clarification! After trying to make use of existing crash_check_hotplug_support API in kernel/crash_core.c, I realize there is no need to explicitly disallow configfs/crash_dm_crypt_key/reuse. Because image->dm_crypt_keys_addr will be set to 0 when crash hotplug is supported. Thus in fact the reuse API has already been implicitly disallowed. So I will drop the unnecessary crash_hotplug_support function in next version. -- Best regards, Coiby