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Mon, 31 Aug 2026 06:35:04 -0700 (PDT) From: Coiby Xu X-Google-Original-From: Coiby Xu Date: Mon, 31 Aug 2026 21:34:30 +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 , Randy Dunlap , "open list:DOCUMENTATION" , open list Subject: Re: [PATCH v4 8/9] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported Message-ID: References: <20260828084900.1496839-1-coiby.xu@gmail.com> <20260828084900.1496839-9-coiby.xu@gmail.com> <38e371e9-1f0a-4e9f-a5e1-0b9d696379da@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <38e371e9-1f0a-4e9f-a5e1-0b9d696379da@linux.ibm.com> On Sun, Aug 30, 2026 at 01:28:59PM +0530, Sourabh Jain wrote: > > >On 28/08/26 14:18, 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. Not reserving >>image->dm_crypt_keys_addr makes it implicitly to disallow using this >>API. 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 | 13 +++++++++---- >> 2 files changed, 19 insertions(+), 10 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 b7629174e4db..3aaa0f9c3117 100644 >>--- a/kernel/crash_dump_dm_crypt.c >>+++ b/kernel/crash_dump_dm_crypt.c >>@@ -324,7 +324,7 @@ static ssize_t config_keys_reuse_store(struct config_item *item, >> r = -EINVAL; >> if (!kexec_crash_image || !kexec_crash_image->dm_crypt_keys_addr) { >>- pr_debug("dm-crypt keys haven't be saved to crash-reserved memory\n"); >>+ pr_debug("dm-crypt keys haven't be saved to crash-reserved memory or crash hotplug supported\n"); > >Nit: the above line is more than 100 characters. There is no >complaint from checkpatch, but I feel we should reduce it to >below 100 characters. Thanks for the reminder! Documentation/process/coding-style.rst explicitly states, However, never break user-visible strings such as printk messages because that breaks the ability to grep for them. In fact, scripts/checkpatch.pl will issue a SPLIT_STRING warning if we break the user-visible strings. So I think this is accepted unless kexec/kdump subsystem has a hard column limit. > >Also, I checked that we don't have pr_fmt defined for this file, >but we do have pr_debug and other pr_* calls. See if defining >pr_fmt helps reduce the character count in the above line. If I'm not mistaken, pr_fmt only adds a prefix. So I don't think it will help reduce the character count in this particular case. > >But the overall idea of handling crash hotplug support with >crash dm-crypt looks good to me. So feel free to add: > >Reviewed-by: Sourabh Jain sourabhjain@linux.ibm.com Thanks for reviewing and ack'ing the patch! > >Thanks, >Sourabh Jain > > >> goto unlock; >> } >>@@ -519,9 +519,9 @@ int crash_load_dm_crypt_keys(struct kimage *image) >> void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) >> { >> /* >>- * For CPU/memory hot-plugging, the kdump image will be reloaded. Prevent >>- * keys_header from being cleaned up during unloading when >>- * is_dm_key_reused=true >>+ * For CPU/memory hot-plugging without CONFIG_CRASH_HOTPLUG, the whole kdump >>+ * image will be reloaded. Prevent keys_header from being cleaned up during >>+ * unloading when is_dm_key_reused=true >> */ >> if (!is_dm_key_reused) { >> kfree_sensitive(keys_header); >>@@ -532,6 +532,11 @@ void kexec_file_post_load_cleanup_dm_crypt(struct kimage *image) >> mutex_unlock(&config_keys_subsys.su_mutex); >> mutex_acquired = false; >> } >>+ >>+#ifdef CONFIG_CRASH_HOTPLUG >>+ if (image->hotplug_support) >>+ image->dm_crypt_keys_addr = 0; >>+#endif >> } >> static int __init configfs_dmcrypt_keys_init(void) > -- Best regards, Coiby