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Subject: Re: [PATCH v2] mm: Fix the problem of mips architecture Oops
To:     zhanglianjie <zhanglianjie@uniontech.com>, jiaxun.yang@flygoat.com,
        chenhuacai@kernel.org, tsbogend@alpha.franken.de
Cc:     linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210628054738.10964-1-zhanglianjie@uniontech.com>
From:   Sergei Shtylyov <sergei.shtylyov@gmail.com>
Organization: Brain-dead Software
Message-ID: <d49404ca-b55c-847d-968d-273ca604b1e6@gmail.com>
Date:   Mon, 28 Jun 2021 11:51:02 +0300
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Hello!

On 28.06.2021 8:47, zhanglianjie wrote:

> The cause of the problem is as follows:
> 1. when cat /sys/devices/system/memory/memory0/valid_zones,
>     test_pages_in_a_zone() will be called.
> 2. test_pages_in_a_zone() finds the zone according to stat_pfn = 0.
>     The smallest pfn of the numa node in the mips architecture is 128,
>     and the page corresponding to the previous 0~127 pfn is not
>     initialized (page->flags is 0xFFFFFFFF)
> 3. The nid and zonenum obtained using page_zone(pfn_to_page(0)) are out
>     of bounds in the corresponding array,
>     &NODE_DATA(page_to_nid(page))->node_zones[page_zonenum(page)],
>     access to the out-of-bounds zone member variables appear abnormal,
>     resulting in Oops.
> Therefore, it is necessary to keep the page between 0 and the minimum
> pfn to prevent Oops from appearing.
> 
> Signed-off-by: zhanglianjie <zhanglianjie@uniontech.com>
> ---
>   arch/mips/loongson64/numa.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/arch/mips/loongson64/numa.c b/arch/mips/loongson64/numa.c
> index fa9b4a487a47..dba9e6f17b9e 100644
> --- a/arch/mips/loongson64/numa.c
> +++ b/arch/mips/loongson64/numa.c
> @@ -129,6 +129,9 @@ static void __init node_mem_init(unsigned int node)
>   		if (node_end_pfn(0) >= (0xffffffff >> PAGE_SHIFT))
>   			memblock_reserve((node_addrspace_offset | 0xfe000000),
>   					 32 << 20);
> +
> +		/* Reserver pfn range 0~node[0]->node_start_pfn */

    Reserve?

> +		memblock_reserve(0, PAGE_SIZE * start_pfn);
>   	}
>   }
[...]

MBR, Sergei