linux-kernel - Re: [PATCH] kho: only fill kimage if KHO is finalized

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Message-ID: <aM0mFDdoQ4r1f9Mo@kernel.org>
Date: Fri, 19 Sep 2025 12:44:52 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Alexander Graf <graf@...zon.com>, Changyuan Lyu <changyuanl@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH] kho: only fill kimage if KHO is finalized

On Thu, Sep 18, 2025 at 07:06:15PM +0200, Pratyush Yadav wrote:
> kho_fill_kimage() only checks for KHO being enabled before filling in
> the FDT to the image. KHO being enabled does not mean that the kernel
> has data to hand over. That happens when KHO is finalized.
> 
> When a kexec is done with KHO enabled but not finalized, the FDT page is
> allocated but not initialized. FDT initialization happens after
> finalize. This means the KHO segment is filled in but the FDT contains
> garbage data.
> 
> This leads to the below error messages in the next kernel:
> 
>     [    0.000000] KHO: setup: handover FDT (0x10116b000) is invalid: -9
>     [    0.000000] KHO: disabling KHO revival: -22
> 
> There is no problem in practice, and the next kernel boots and works
> fine. But this still leads to misleading error messages and garbage
> being handed over.
> 
> Only fill in KHO segment when KHO is finalized. When KHO is not enabled,
> the debugfs interface is not created and there is no way to finalize it
> anyway. So the check for kho_enable is not needed, and kho_out.finalize
> alone is enough.
> 
> Fixes: 3bdecc3c93f9f ("kexec: add KHO support to kexec file loads")
> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>

Nice catch!

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  kernel/kexec_handover.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index 8079fc4b9189..5ff959a90165 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -1242,7 +1242,7 @@ int kho_fill_kimage(struct kimage *image)
>  	int err = 0;
>  	struct kexec_buf scratch;
>  
> -	if (!kho_enable)
> +	if (!kho_out.finalized)
>  		return 0;
>  
>  	image->kho.fdt = page_to_phys(kho_out.ser.fdt);
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.