Re: [PATCH v2] kho: skip KHO for crash kernel

[Mike Rapoport]

On Fri, Apr 10, 2026 at 01:16:05AM +0000, Evangelos Petrongonas wrote:
> kho_fill_kimage() unconditionally populates the kimage with KHO
> metadata for every kexec image type. When the image is a crash kernel,
> this can be problematic as the crash kernel can run in a small reserved
> region and the KHO scratch areas can sit outside it.
> The crash kernel then faults during kho_memory_init() when it
> tries phys_to_virt() on the KHO FDT address:
> 
>   Unable to handle kernel paging request at virtual address xxxxxxxx
>   ...
>     fdt_offset_ptr+...
>     fdt_check_node_offset_+...
>     fdt_first_property_offset+...
>     fdt_get_property_namelen_+...
>     fdt_getprop+...
>     kho_memory_init+...
>     mm_core_init+...
>     start_kernel+...
> 
> kho_locate_mem_hole() already skips KHO logic for KEXEC_TYPE_CRASH
> images, but kho_fill_kimage() was missing the same guard. As
> kho_fill_kimage() is the single point that populates image->kho.fdt
> and image->kho.scratch, fixing it here is sufficient for both arm64
> and x86 as the FDT and boot_params path are bailing out when these
> fields are unset.
> 
> Fixes: d7255959b69a ("kho: allow kexec load before KHO finalization")
> Signed-off-by: Evangelos Petrongonas <epetron@xxxxxxxxx>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>

> ---
> 
> v2: Per Mike's review [1], move the guard into kho_fill_kimage() instead
>     of patching the arch-level producers and consumers. This fixes
>     both arm64 and x86 in one place and avoids redundant checks. Tested again.
> 
> Note regarding backporting
> The offending commit was deployed with 6.19. The only other supported
> kernel version with 6.18, unless I miss someting uses
> ```
> if (!kho_out.finalized)
> ```
> which in the case of crash kernel it shouldn't be finalised.

Yes, this seems about right :) 
The only released kernel that has this issue is v6.19 and it will be EOL in
less than a week.
 
> [1] https://lore.kernel.org/all/ade2ExpM8ROXV-vy@xxxxxxxxxx/
> 
>  kernel/liveupdate/kexec_handover.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index cc68a3692905..1029fe8778f2 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -1551,7 +1551,7 @@ int kho_fill_kimage(struct kimage *image)
>  	int err = 0;
>  	struct kexec_buf scratch;
>  
> -	if (!kho_enable)
> +	if (!kho_enable || image->type == KEXEC_TYPE_CRASH)
>  		return 0;
>  
>  	image->kho.fdt = virt_to_phys(kho_out.fdt);
> -- 
> 2.47.3
> 
> 
> 
> 
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-- 
Sincerely yours,
Mike.