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From:   zhanglianjie <zhanglianjie@uniontech.com>
To:     tsbogend@alpha.franken.de
Cc:     linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,
        tangyouling@loongson.cn, zhanglianjie <zhanglianjie@uniontech.com>
Subject: [PATCH] mm: Fix the problem of mips architecture Oops
Date:   Thu, 24 Jun 2021 11:22:12 +0800
Message-Id: <20210624032212.24769-1-zhanglianjie@uniontech.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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/kernel/setup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 23a140327a0b..f1da2b2ba5e9 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -653,6 +653,8 @@ static void __init arch_mem_init(char **cmdline_p)
 	 */
 	memblock_set_current_limit(PFN_PHYS(max_low_pfn));

+	memblock_reserve(0, PAGE_SIZE * NODE_DATA(0)->node_start_pfn);
+
 	mips_reserve_vmcore();

 	mips_parse_crashkernel();
--
2.20.1