[PATCH v12 3/6] crash: add a new kexec flag for FDT update

[Sourabh Jain <sourabhjain@linux.ibm.com>]

The commit a72bbec70da2 ("crash: hotplug support for kexec_load()")
introduced a new kexec flag, `KEXEC_UPDATE_ELFCOREHDR`. Kexec tool uses
this flag to indicate kernel that it is safe to modify the elfcorehdr
of kdump image loaded using kexec_load system call.

Similarly, add a new kexec flag, `KEXEC_UPDATE_FDT`, for another kdump
component named FDT (Flatten Device Tree). Architectures like PowerPC
need to update FDT kdump image component on CPU hotplug events. Kexec
tool passing `KEXEC_UPDATE_FDT` will be an indication to kernel that FDT
segment is not part of SHA calculation hence it is safe to update it.

With the `KEXEC_UPDATE_ELFCOREHDR` and `KEXEC_UPDATE_FDT` kexec flags,
crash hotplug support can be added to PowerPC for the kexec_load syscall
while maintaining the backward compatibility with older kexec tools that
do not have these newly introduced flags.

Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Akhil Raj <lf32.dev@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Eric DeVolder <eric.devolder@oracle.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: Laurent Dufour <laurent.dufour@fr.ibm.com>
Cc: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mimi Zohar <zohar@linux.ibm.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: kexec@lists.infradead.org
Cc: x86@kernel.org
---
 include/linux/kexec.h      | 6 ++++--
 include/uapi/linux/kexec.h | 1 +
 kernel/kexec.c             | 2 ++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index e9f70d7b7d16..16f03e79d82f 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -323,6 +323,7 @@ struct kimage {
 #ifdef CONFIG_CRASH_HOTPLUG
 	/* If set, allow changes to elfcorehdr of kexec_load'd image */
 	unsigned int update_elfcorehdr:1;
+	unsigned int update_fdt:1;
 #endif
 
 #ifdef ARCH_HAS_KIMAGE_ARCH
@@ -400,9 +401,10 @@ bool kexec_load_permitted(int kexec_image_type);
 
 /* List of defined/legal kexec flags */
 #ifndef CONFIG_KEXEC_JUMP
-#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR)
+#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_UPDATE_ELFCOREHDR | KEXEC_UPDATE_FDT)
 #else
-#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR)
+#define KEXEC_FLAGS    (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT | KEXEC_UPDATE_ELFCOREHDR | \
+			KEXEC_UPDATE_FDT)
 #endif
 
 /* List of defined/legal kexec file flags */
diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
index 01766dd839b0..3d5b3d757bed 100644
--- a/include/uapi/linux/kexec.h
+++ b/include/uapi/linux/kexec.h
@@ -13,6 +13,7 @@
 #define KEXEC_ON_CRASH		0x00000001
 #define KEXEC_PRESERVE_CONTEXT	0x00000002
 #define KEXEC_UPDATE_ELFCOREHDR	0x00000004
+#define KEXEC_UPDATE_FDT	0x00000008
 #define KEXEC_ARCH_MASK		0xffff0000
 
 /*
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 107f355eac10..baf3fe39fce7 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -132,6 +132,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
 #ifdef CONFIG_CRASH_HOTPLUG
 	if (flags & KEXEC_UPDATE_ELFCOREHDR)
 		image->update_elfcorehdr = 1;
+	if (flags & KEXEC_UPDATE_FDT)
+		image->update_fdt = 1;
 #endif
 
 	ret = machine_kexec_prepare(image);
-- 
2.41.0