linux-kernel - Re: [PATCH v5 3/3] kexec: Introduce sysctl parameters kexec_load_limit

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Date:   Sun, 1 Jan 2023 21:08:33 +0100
From:   Petr Tesařík <petr@...arici.cz>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Jonathan Corbet <corbet@....net>,
        Philipp Rudo <prudo@...hat.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        kexec@...ts.infradead.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v5 3/3] kexec: Introduce sysctl parameters
 kexec_load_limit_*

Hi Ricardo,

On Wed, 21 Dec 2022 20:45:59 +0100
Ricardo Ribalda <ribalda@...omium.org> wrote:

> Add two parameters to specify how many times a kexec kernel can be loaded.
> 
> The sysadmin can set different limits for kexec panic and kexec reboot
> kernels.
> 
> The value can be modified at runtime via sysctl, but only with a value
> smaller than the current one (except -1).
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  Documentation/admin-guide/sysctl/kernel.rst | 18 ++++++
>  include/linux/kexec.h                       |  2 +-
>  kernel/kexec.c                              |  4 +-
>  kernel/kexec_core.c                         | 87 ++++++++++++++++++++++++++++-
>  kernel/kexec_file.c                         | 11 ++--
>  5 files changed, 114 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index 97394bd9d065..a3922dffbd47 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -461,6 +461,24 @@ allowing a system to set up (and later use) an image without it being
>  altered.
>  Generally used together with the `modules_disabled`_ sysctl.
>  
> +kexec_load_limit_panic
> +======================
> +
> +This parameter specifies a limit to the number of times the syscalls
> +``kexec_load`` and ``kexec_file_load`` can be called with a crash
> +image. It can only be set with a more restrictive value than the
> +current one.
> +
> +=  =============================================================
> +-1 Unlimited calls to kexec. This is the default setting.
> +N  Number of calls left.
> +=  =============================================================
> +
> +kexec_load_limit_reboot
> +======================
> +
> +Similar functionality as ``kexec_load_limit_panic``, but for a crash
> +image.

Is this description correct? IIUC the ``kexec_load_limit_panic`` is for
the crash image, and ``kexec_load_limit_reboot`` is for the normal
image, but the sentence above says again: "for a crash image."

Petr T