From bdf90d473194123c6454f39790a72fa092907caa Mon Sep 17 00:00:00 2001

From: Naoya Horiguchi <naoya.horiguchi@nec.com>

Date: Thu, 2 Sep 2021 14:57:07 -0700

Subject: [PATCH] mm/sparse: set SECTION_NID_SHIFT to 6

References: bsc#1190208 (MM functional and performance backports)

Patch-mainline: v5.15-rc1

Git-commit: 01c8d337d195ed105cabab95bc4dcb9e145bf5ea

Currently SECTION_NID_SHIFT is set to 3, which is incorrect because bit 3

and 4 can be overlapped by sub-field for early NID, and can be

unexpectedly set on NUMA systems.  There are a few non-critical issues

related to this:

- Having SECTION_TAINT_ZONE_DEVICE set for wrong sections forces

  pfn_to_online_page() through the slow path, but doesn't actually break

  the kernel.

- A kdump generation tool like makedumpfile uses this field to calculate

  the physical address to read.  So wrong bits can make the tool access to

  wrong address and fail to create kdump.  This can be avoided by the

  tool, so it's not critical.

To fix it, set SECTION_NID_SHIFT to 6 which is the minimum number of

available bits of section flag field.

Link: https://lkml.kernel.org/r/20210707045548.810271-1-naoya.horiguchi@linux.dev

Fixes: 1f90a3477df3 ("mm: teach pfn_to_online_page() about ZONE_DEVICE section collisions")

Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>

Reported-by: Kazuhito Hagio <k-hagio-ab@nec.com>

Suggested-by: Dan Williams <dan.j.williams@intel.com>

Acked-by: David Hildenbrand <david@redhat.com>

Cc: Oscar Salvador <osalvador@suse.de>

Cc: Wang Wensheng <wangwensheng4@huawei.com>

Cc: Rui Xiang <rui.xiang@huawei.com>

Cc: Kazu <k-hagio-ab@nec.com>

Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Signed-off-by: Mel Gorman <mgorman@suse.de>

---

 include/linux/mmzone.h | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h

index 8827f4d081d4..59bad25ce78e 100644

--- a/include/linux/mmzone.h

+++ b/include/linux/mmzone.h

@@ -1364,7 +1364,7 @@ extern size_t mem_section_usage_size(void);

 #define SECTION_TAINT_ZONE_DEVICE	(1UL<<4)

 #define SECTION_MAP_LAST_BIT		(1UL<<5)

 #define SECTION_MAP_MASK		(~(SECTION_MAP_LAST_BIT-1))

-#define SECTION_NID_SHIFT		3

+#define SECTION_NID_SHIFT		6

 static inline struct page *__section_mem_map_addr(struct mem_section *section)

 {