linux-kernel - Re: [PATCH v2 0/2] x86/kexec: Carry forward the boot DTB on kexec

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Message-ID: <A402BEF1-EB1A-48F0-997F-502429AAD92E@juniper.net>
Date: Wed, 13 Aug 2025 19:24:37 +0000
From: Brian Mak <makb@...iper.net>
To: Dave Young <dyoung@...hat.com>
CC: Baoquan He <bhe@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Graf <graf@...zon.com>, 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>, 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 v2 0/2] x86/kexec: Carry forward the boot DTB on kexec

On Aug 12, 2025, at 8:54 PM, Dave Young <dyoung@...hat.com> wrote:

> Hi, The #ifdef CONFIG_* which can be replaced by #if defined(), but I
> do not have a strong opinion.  other than that do you have kexec-tools
> patch ready? It would be better to provide a link so that people can
> try and test it.

Hi Dave,

Thanks for looking at this! The #ifdef CONFIG_* is used, as it matches
the style of other ifdefs in this file. I'd like to keep it as-is for
consistency.

I do have a prototype kexec-tools patch ready for testing. The changes
can be found at this repo:

https://github.com/makb-juniper/kexec-tools.git

I've also placed the diff below.

Thanks,
Brian

diff --git a/kexec/kexec-syscall.h b/kexec/kexec-syscall.h
index 9b17578..8419b23 100644
--- a/kexec/kexec-syscall.h
+++ b/kexec/kexec-syscall.h
@@ -124,6 +124,8 @@ static inline long kexec_file_load(int kernel_fd, int initrd_fd,
 #define KEXEC_FILE_ON_CRASH	0x00000002
 #define KEXEC_FILE_NO_INITRAMFS	0x00000004
 #define KEXEC_FILE_DEBUG	0x00000008
+#define KEXEC_FILE_NO_CMA	0x00000010
+#define KEXEC_FILE_FORCE_DTB	0x00000020
 
 /* These values match the ELF architecture values. 
  * Unless there is a good reason that should continue to be the case.
diff --git a/kexec/kexec.c b/kexec/kexec.c
index 6bf12d7..0e13b6b 100644
--- a/kexec/kexec.c
+++ b/kexec/kexec.c
@@ -1102,6 +1102,7 @@ void usage(void)
 	       " --hotplug            Do in-kernel update of kexec segments on CPU/Memory\n"
 	       "                      hot add/remove events, avoiding the need to reload\n"
 	       "                      kdump kernel on online/offline events.\n"
+	       " --force-dtb          Carry over the current boot's device tree blob (x86 only).\n"
 	       " -d, --debug          Enable debugging to help spot a failure.\n"
 	       " -S, --status         Return 1 if the type (by default crash) is loaded,\n"
 	       "                      0 if not.\n"
@@ -1640,6 +1641,9 @@ int main(int argc, char *argv[])
 		case OPT_HOTPLUG:
 			do_hotplug = 1;
 			break;
+		case OPT_FORCE_DTB:
+			kexec_file_flags |= KEXEC_FILE_FORCE_DTB;
+			break;
 		default:
 			break;
 		}
diff --git a/kexec/kexec.h b/kexec/kexec.h
index a2e19c4..2235aa2 100644
--- a/kexec/kexec.h
+++ b/kexec/kexec.h
@@ -235,7 +235,8 @@ extern int file_types;
 #define OPT_LOAD_LIVE_UPDATE	263
 #define OPT_EXEC_LIVE_UPDATE	264
 #define OPT_HOTPLUG		        265
-#define OPT_MAX		266
+#define OPT_FORCE_DTB		266
+#define OPT_MAX		267
 #define KEXEC_OPTIONS \
 	{ "help",		0, 0, OPT_HELP }, \
 	{ "version",		0, 0, OPT_VERSION }, \
@@ -263,6 +264,7 @@ extern int file_types;
 	{ "status",		0, 0, OPT_STATUS }, \
 	{ "print-ckr-size",     0, 0, OPT_PRINT_CKR_SIZE }, \
 	{ "hotplug",		    0, 0, OPT_HOTPLUG }, \
+	{ "force-dtb",          0, 0, OPT_FORCE_DTB }, \
 
 #define KEXEC_OPT_STR "h?vdfixyluet:pscaS"
 

base-commit: daa29443819d3045338792b5ba950ed90e79d7a5
-- 
2.25.1