linux-kernel - Re: [PATCH] mm: ignore nomap memory during mirror init

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Message-ID: <aHjQp9zPVPuPyP3B@kernel.org>
Date: Thu, 17 Jul 2025 13:29:59 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Wupeng Ma <mawupeng1@...wei.com>
Cc: akpm@...ux-foundation.org, ardb@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: ignore nomap memory during mirror init

On Thu, Jul 17, 2025 at 04:57:23PM +0800, Wupeng Ma wrote:
> When memory mirroring is enabled, the BIOS may reserve memory regions
> at the start of the physical address space without the MR flag. This will
> lead to zone_movable_pfn to be updated to the start of these reserved
> regions, resulting in subsequent mirrored memory being ignored.
> 
> Here is the log with efi=debug enabled:
>   efi:   0x084004000000-0x0842bf37ffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
>   efi:   0x0842bf380000-0x0842c21effff [Loader Code |   |  |MR|...|WB|WT|WC|  ]
>   efi:   0x0842c21f0000-0x0847ffffffff [Conventional|   |  |MR|...|WB|WT|WC|  ]
>   efi:   0x085000000000-0x085fffffffff [Conventional|   |  |  |...|WB|WT|WC|  ]
> ...
>   efi:   0x084000000000-0x084003ffffff [Reserved    |   |  |  |...|WB|WT|WC|  ]
> 
> Since this kind of memory can not be used by kernel. ignore nomap memory to fix
> this issue.

If the memory is nomap it won't be used by the kernel anyway.
What's the actual issue you are trying to fix?
 
> Signed-off-by: Wupeng Ma <mawupeng1@...wei.com>
> ---
>  mm/mm_init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f2944748f526..1c36518f0fe4 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -405,7 +405,7 @@ static void __init find_zone_movable_pfns_for_nodes(void)
>  		}
>  
>  		for_each_mem_region(r) {
> -			if (memblock_is_mirror(r))
> +			if (memblock_is_mirror(r) || memblock_is_nomap(r))
>  				continue;
>  
>  			nid = memblock_get_region_node(r);
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.