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Date:   Mon, 12 Sep 2022 11:47:14 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Eric DeVolder <eric.devolder@oracle.com>, bp@alien8.de,
        akpm@linux-foundation.org, x86@kernel.org
Cc:     linux-kernel@vger.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,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com
Subject: Re: [PATCH v12 0/7] crash: Kernel handling of CPU and memory hot
 un/plug
Message-ID: <Yx6rwt+nMybIzlAz@MiWiFi-R3L-srv>
References: <20220909210509.6286-1-eric.devolder@oracle.com>
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On 09/09/22 at 05:05pm, Eric DeVolder wrote:
> When the kdump service is loaded, if a CPU or memory is hot
> un/plugged, the crash elfcorehdr, which describes the CPUs
> and memory in the system, must also be updated, else the resulting
> vmcore is inaccurate (eg. missing either CPU context or memory
> regions).
> 
> The current solution utilizes udev to initiate an unload-then-reload
> of the kdump image (e. kernel, initrd, boot_params, puratory and
> elfcorehdr) by the userspace kexec utility. In previous posts I have
> outlined the significant performance problems related to offloading
> this activity to userspace.
> 
> This patchset introduces a generic crash hot un/plug handler that
> registers with the CPU and memory notifiers. Upon CPU or memory
> changes, this generic handler is invoked and performs important
> housekeeping, for example obtaining the appropriate lock, and then
> invokes an architecture specific handler to do the appropriate
> updates.
> 
> In the case of x86_64, the arch specific handler generates a new
> elfcorehdr, and overwrites the old one in memory. No involvement
> with userspace needed.

Thank a lot for all the effort, Eric.

Hi Boris, Andrew,

This version looks good to me. It introduces a framework for kdump
to react mem/cpu hotplug eveut and add x86 handler. Should this go
to x86 tree or mm tree? Please check what else we need do to fix or
improve.

Thanks
Baoquan