linux-kernel - [PATCH] mm/memory_hotplug: fix default_zone_for

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Message-ID: <20200604133938.GA1513@cosmos>
Date:   Thu, 4 Jun 2020 19:09:42 +0530
From:   Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mm/memory_hotplug: fix default_zone_for_pfn() to include
 highmem zone range

On x86_32, while onlining highmem sections, the func default_zone_for_pfn()
defaults target zone to ZONE_NORMAL (movable_node_enabled = 0). Onlining of
pages is successful, and these highmem pages are moved into zone_normal.

As a consequence, these pages are treated as low mem, and page addresses
are calculated using lowmem_page_address() which effectively overflows the
32 bit virtual addresses, leading to kernel panics and system becomes
unusable.

Change default_kernel_zone_for_pfn() to intersect highmem pfn range, and
calculate the default zone accordingly.

Signed-off-by: Vamshi K Sthambamkadi <vamshi.k.sthambamkadi@...il.com>
---
 mm/memory_hotplug.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c4d5c45..30f101a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -725,8 +725,13 @@ static struct zone *default_kernel_zone_for_pfn(int nid, unsigned long start_pfn
 {
 	struct pglist_data *pgdat = NODE_DATA(nid);
 	int zid;
+	int nr_zones = ZONE_NORMAL;

-	for (zid = 0; zid <= ZONE_NORMAL; zid++) {
+#ifdef CONFIG_HIGHMEM
+	nr_zones = ZONE_HIGHMEM;
+#endif
+
+	for (zid = 0; zid <= nr_zones; zid++) {
 		struct zone *zone = &pgdat->node_zones[zid];

 		if (zone_intersects(zone, start_pfn, nr_pages))
-- 
2.7.4