linux-kernel - Re: [PATCH RESEND] x86/kexec: Carry forward the boot DTB on kexec

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Message-ID: <5A9FE2FF-800A-4458-9929-124EB89FE1D9@juniper.net>
Date: Fri, 1 Aug 2025 19:24:26 +0000
From: Brian Mak <makb@...iper.net>
To: Baoquan He <bhe@...hat.com>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org"
	<kexec@...ts.infradead.org>,
        "devicetree@...r.kernel.org"
	<devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] x86/kexec: Carry forward the boot DTB on kexec

On Jul 31, 2025, at 8:02 PM, Baoquan He <bhe@...hat.com> wrote:

> On 07/29/25 at 11:21am, Brian Mak wrote:
>> The kexec_file_load syscall on x86 currently does not support passing
>> a device tree blob to the new kernel.
>> 
>> To add support for this, we copy the behavior of ARM64 and PowerPC and
>> copy the current boot's device tree blob for use in the new kernel. We
>> do this on x86 by passing the device tree blob as a setup_data entry in
>> accordance with the x86 boot protocol.
> 
> I see how, but no why. Why do we need to add DTB for x86?

Hi Baoquan,

Thanks for your comment. Some embedded x86 systems, such as ours at
Juniper, use device trees. Currently, the x86 kexec_file_load syscall
has no support for passing the device tree to the new kernel, which is a
problem for us since we use kexec for some software upgrade related
features. Not passing a device tree to the new kernel would cause a boot
failure here.

Thanks,
Brian