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

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Message-ID: <aI7gBld/+yKQ2EXM@MiWiFi-R3L-srv>
Date: Sun, 3 Aug 2025 12:05:26 +0800
From: Baoquan He <bhe@...hat.com>
To: Brian Mak <makb@...iper.net>
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 08/01/25 at 07:24pm, Brian Mak wrote:
> 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 for the info. Please add these into patch log to let reviewers
know them. We don't add code w/o objective.