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Date:   Mon, 21 Mar 2022 19:59:40 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Eric DeVolder <eric.devolder@oracle.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
Subject: Re: [PATCH v5 2/8] x86/crash hp: Introduce CRASH_HOTPLUG
 configuration options
Message-ID: <20220321115940.GA354864@MiWiFi-R3L-srv>
References: <20220303162725.49640-1-eric.devolder@oracle.com>
 <20220303162725.49640-3-eric.devolder@oracle.com>
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On 03/03/22 at 11:27am, Eric DeVolder wrote:
> Support for CPU and memory hotplug for crash is controlled by the
> CRASH_HOTPLUG configuration option, introduced by this patch.
> 
> The CRASH_HOTPLUG_ELFCOREHDR_SZ related configuration option is
> also introduced with this patch.

Maybe can rephrase it as:

x86/crash: Introduce new options to support cpu and memory hotplug of crash
 
CRASH_HOTPLUG is to enable cpu and memory hotplug of crash.

CRASH_HOTPLUG_ELFCOREHDR_SZ is used to Specify the maximum size of
the elfcorehdr buffer/segment.
 
This is a preparation for later usage.

Otherwise, this looks good to me.


> 
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
>  arch/x86/Kconfig | 26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 9f5bd41bf660..37eb26563f07 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2061,6 +2061,32 @@ config CRASH_DUMP
>  	  (CONFIG_RELOCATABLE=y).
>  	  For more details see Documentation/admin-guide/kdump/kdump.rst
>  
> +config CRASH_HOTPLUG
> +	bool "kernel updates of crash elfcorehdr"
> +	depends on CRASH_DUMP && (HOTPLUG_CPU || MEMORY_HOTPLUG) && KEXEC_FILE
> +	help
> +	  Enable the kernel to update the crash elfcorehdr (which contains
> +	  the list of CPUs and memory regions) directly when hot plug/unplug
> +	  of CPUs or memory. Otherwise userspace must monitor these hot
> +	  plug/unplug change notifications via udev in order to
> +	  unload-then-reload the crash kernel so that the list of CPUs and
> +	  memory regions is kept up-to-date. Note that the udev CPU and
> +	  memory change notifications still occur (however, userspace is not
> +	  required to monitor for crash dump purposes).
> +
> +config CRASH_HOTPLUG_ELFCOREHDR_SZ
> +	depends on CRASH_HOTPLUG
> +	int
> +	default 131072
> +	help
> +	  Specify the maximum size of the elfcorehdr buffer/segment.
> +	  The 128KiB default is sized so that it can accommodate 2048
> +	  Elf64_Phdr, where each Phdr represents either a CPU or a
> +	  region of memory.
> +	  For example, this size can accommodate a machine with up to 1024
> +	  CPUs and up to 1024 memory regions, eg. as represented by the
> +	  'System RAM' entries in /proc/iomem.
> +
>  config KEXEC_JUMP
>  	bool "kexec jump"
>  	depends on KEXEC && HIBERNATION
> -- 
> 2.27.0
>