[PATCH] kho: only fill kimage if KHO is finalized

[PATCH] kho: only fill kimage if KHO is finalized

[Pratyush Yadav]

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@kernel.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

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

[Mike Rapoport]

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@kernel.org>

Nice catch!

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.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.