[PATCH v3] memory hotplug: update the variables after memory removed

[Zhang Zhen <zhenzhang.zhang@huawei.com>]

Commit ea0854170c95 ("memory hotplug: fix a bug on /dev/mem
for 64-bit kernels") added a fuction update_end_of_memory_vars()
to update high_memory, max_pfn and max_low_pfn.

Here we may access wrong memory via /dev/mem after memory remove
without this patch.
I modified the function and call it in arch_remove_memory() to update
these variables too.

Change v1->v2:
- according to Dave Hansen and David Rientjes's suggestions modified
  update_end_of_memory_vars().
change v2->v3:
- remove the extra space before the function identifier of
  update_end_of_memory_vars().
- remove the end_pfn and use start_pfn + nr_pages in the conditional.

Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 arch/x86/mm/init_64.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index df1a992..d16368e 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -673,15 +673,11 @@ void __init paging_init(void)
  * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
  * updating.
  */
-static void  update_end_of_memory_vars(u64 start, u64 size)
+static void update_end_of_memory_vars(u64 end_pfn)
 {
-	unsigned long end_pfn = PFN_UP(start + size);
-
-	if (end_pfn > max_pfn) {
-		max_pfn = end_pfn;
-		max_low_pfn = end_pfn;
-		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
-	}
+	max_pfn = end_pfn;
+	max_low_pfn = end_pfn;
+	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
 }

 /*
@@ -694,6 +690,7 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	struct zone *zone = pgdat->node_zones + ZONE_NORMAL;
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
+	unsigned long end_pfn;
 	int ret;

 	init_memory_mapping(start, start + size);
@@ -702,7 +699,9 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	WARN_ON_ONCE(ret);

 	/* update max_pfn, max_low_pfn and high_memory */
-	update_end_of_memory_vars(start, size);
+	end_pfn = start_pfn + nr_pages;
+	if (end_pfn > max_pfn)
+		update_end_of_memory_vars(end_pfn);

 	return ret;
 }
@@ -1025,6 +1024,10 @@ int __ref arch_remove_memory(u64 start, u64 size)
 	ret = __remove_pages(zone, start_pfn, nr_pages);
 	WARN_ON_ONCE(ret);

+	/* update max_pfn, max_low_pfn and high_memory */
+	if ((max_pfn >= start_pfn) && (max_pfn < (start_pfn + nr_pages)))
+		update_end_of_memory_vars(start_pfn);
+
 	return ret;
 }
 #endif
-- 
1.8.1.2


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