Re: [PATCH v14 3/6] crash: add a new kexec flag for FDT update

[Baoquan He <bhe@redhat.com>]

On 12/11/23 at 02:00pm, Sourabh Jain wrote:
> 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: Aneesh Kumar K.V <aneesh.kumar@kernel.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: Naveen N Rao <naveen@kernel.org>
> 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 0f6ea35879ee..bcedb7625b1f 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -319,6 +319,7 @@ 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;

Can we unify this to one flag, e.g hotplug_update?

With this, on x86_64, we will skip the sha calculation for elfcorehdr. 
On ppc, we will skip the sha calculation for elfcorehdr and fdt.

>  #endif
>  
>  #ifdef ARCH_HAS_KIMAGE_ARCH
> @@ -396,9 +397,10 @@ 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 8f35a5a42af8..97eb151cd931 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
> 


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