Re: [PATCH v3 09/10] crash_dump: Disallow configfs/crash_dm_crypt_key/reuse if crash hotplug supported

[Coiby Xu]

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 <coiby.xu@xxxxxxxxx>
> > ---
> >  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?

> - Sourabh Jain
[...]

--
Best regards,
Coiby