linux-kernel - Re: [PATCH v3 4/7] kho: replace KHO FDT with kstate metadata

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Message-ID: <20250910165010.GA223810-robh@kernel.org>
Date: Wed, 10 Sep 2025 11:50:10 -0500
From: Rob Herring <robh@...nel.org>
To: Andrey Ryabinin <arbn@...dex-team.com>
Cc: linux-kernel@...r.kernel.org, Alexander Graf <graf@...zon.com>,
	Mike Rapoport <rppt@...nel.org>, James Gowans <jgowans@...zon.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Baoquan He <bhe@...hat.com>,
	kexec@...ts.infradead.org, Pratyush Yadav <ptyadav@...zon.de>,
	Jason Gunthorpe <jgg@...dia.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	David Rientjes <rientjes@...gle.com>,
	Pratyush Yadav <pratyush@...nel.org>,
	Changyuan Lyu <changyuanl@...gle.com>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Chris Li <chrisl@...nel.org>, Ashish.Kalra@....com,
	William Tu <witu@...dia.com>, David Matlack <dmatlack@...gle.com>,
	Saravana Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org
Subject: Re: [PATCH v3 4/7] kho: replace KHO FDT with kstate metadata

On Tue, Sep 09, 2025 at 10:14:39PM +0200, Andrey Ryabinin wrote:
> Store KSTATE physical address & size instead of FDT in kho_data.
> and initialize KSTATE from kho_populate().
> To be able to use FDT in parallel with KSTATE place FDT
> address&size into 'struct kho_fdt' and save/restore it using KSTATE.
> 
> This finishes wiring KSTATE with KHO, making it fully functional.
> 
> Signed-off-by: Andrey Ryabinin <arbn@...dex-team.com>
> ---
>  arch/x86/include/uapi/asm/setup_data.h |  4 +-
>  arch/x86/kernel/kexec-bzimage64.c      |  6 +--
>  arch/x86/kernel/setup.c                |  3 +-
>  drivers/of/fdt.c                       |  6 +--
>  include/linux/kexec.h                  |  2 +-
>  include/linux/kstate.h                 |  1 +
>  kernel/liveupdate/kexec_handover.c     | 60 +++++++++++++++++++++-----
>  7 files changed, 61 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/include/uapi/asm/setup_data.h b/arch/x86/include/uapi/asm/setup_data.h
> index 2671c4e1b3a0..844f5b93473f 100644
> --- a/arch/x86/include/uapi/asm/setup_data.h
> +++ b/arch/x86/include/uapi/asm/setup_data.h
> @@ -83,8 +83,8 @@ struct ima_setup_data {
>   * Locations of kexec handover metadata
>   */
>  struct kho_data {
> -	__u64 fdt_addr;
> -	__u64 fdt_size;
> +	__u64 kstate_addr;
> +	__u64 kstate_size;
>  	__u64 scratch_addr;
>  	__u64 scratch_size;
>  } __attribute__((packed));

Isn't this part of the ABI which you can't just change.

Rob