linux-kernel - Re: [PATCH] arm64: mm: Correct the update of max

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Message-ID: <48f15771-ed1a-4e30-b825-70ee3c323d37@arm.com>
Date: Mon, 24 Mar 2025 09:49:38 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Zhenhua Huang <quic_zhenhuah@...cinc.com>, catalin.marinas@....com,
 david@...hat.com, will@...nel.org, ryan.roberts@....com,
 mark.rutland@....com, ardb@...nel.org, yangyicong@...ilicon.com,
 joey.gouly@....com, quic_cgoldswo@...cinc.com, quic_sudaraja@...cinc.com,
 akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, quic_tingweiz@...cinc.com
Subject: Re: [PATCH] arm64: mm: Correct the update of max_pfn

On 3/21/25 12:30, Zhenhua Huang wrote:
> Hotplugged memory can be smaller than the original memory. For example,
> on my target:
> 
> root@...ericarmv8:~# cat /sys/kernel/debug/memblock/memory
>    0: 0x0000000064005000..0x0000000064023fff    0 NOMAP
>    1: 0x0000000064400000..0x00000000647fffff    0 NOMAP
>    2: 0x0000000068000000..0x000000006fffffff    0 DRV_MNG
>    3: 0x0000000088800000..0x0000000094ffefff    0 NONE
>    4: 0x0000000094fff000..0x0000000094ffffff    0 NOMAP
> max_pfn will affect read_page_owner. Therefore, it should first compare and
> then select the larger value for max_pfn.
> 
> Fixes: 8fac67ca236b ("arm64: mm: update max_pfn after memory hotplug")
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@...cinc.com>
> ---
>  arch/arm64/mm/mmu.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1dfe1a8efdbe..310ff75891ef 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1361,7 +1361,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  		__remove_pgd_mapping(swapper_pg_dir,
>  				     __phys_to_virt(start), size);
>  	else {
> -		max_pfn = PFN_UP(start + size);
> +		/* Address of hotplugged memory can be smaller */
> +		max_pfn = max(max_pfn, PFN_UP(start + size));
>  		max_low_pfn = max_pfn;
>  	}
>  

Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>