Re: [PATCH] mm/memblock: only mark/clear KHO scratch memory when needed

[Mike Rapoport <rppt@kernel.org>]

On Wed, Nov 26, 2025 at 07:20:51AM +0000, Usama Arif wrote:
> The scratch memory for kexec handover is used to bootstrap the
> kexec'ed kernel. It is only needed when CONFIG_MEMBLOCK_KHO_SCRATCH
> is enabled (selected by KHO) and if it is a KHO boot. Add checks
> to prevent marking a KHO scratch region unless needed.
> 
> kexec_handover.h is now unconditionally included for is_kho_boot.
> 
> Fixes: a2daf83e10378 ("x86/e820: temporarily enable KHO scratch for memory below 1M")
> Reported-by: Vlad Poenaru <thevlad@meta.com>
> Signed-off-by: Usama Arif <usamaarif642@gmail.com>
> ---
>  mm/memblock.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index e23e16618e9b3..5c85d575bb61c 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -20,8 +20,8 @@
>  
>  #ifdef CONFIG_KEXEC_HANDOVER
>  #include <linux/libfdt.h>
> -#include <linux/kexec_handover.h>
>  #endif /* CONFIG_KEXEC_HANDOVER */
> +#include <linux/kexec_handover.h>
>  
>  #include <asm/sections.h>
>  #include <linux/io.h>
> @@ -1126,8 +1126,11 @@ int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t
>   */
>  __init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
>  {
> -	return memblock_setclr_flag(&memblock.memory, base, size, 1,
> -				    MEMBLOCK_KHO_SCRATCH);
> +	if (IS_ENABLED(CONFIG_MEMBLOCK_KHO_SCRATCH) && is_kho_boot())
> +		return memblock_setclr_flag(&memblock.memory, base, size, 1,
> +					    MEMBLOCK_KHO_SCRATCH);
> +	else

else is not needed.

> +		return 0;
>  }
>  
>  /**
> @@ -1140,8 +1143,11 @@ __init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
>   */
>  __init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
>  {
> -	return memblock_setclr_flag(&memblock.memory, base, size, 0,
> -				    MEMBLOCK_KHO_SCRATCH);
> +	if (IS_ENABLED(CONFIG_MEMBLOCK_KHO_SCRATCH) && is_kho_boot())
> +		return memblock_setclr_flag(&memblock.memory, base, size, 0,
> +					    MEMBLOCK_KHO_SCRATCH);
> +	else

Ditto.

> +		return 0;
>  }
>  
>  static bool should_skip_region(struct memblock_type *type,
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.