[PATCH] memblock: fix page count when preserving reserve_mem regions

[Sang-Heon Jeon <ekffu200098@gmail.com>]

When map->start or map->size is not page aligned,
reserved_mem_preserve() does not preserve the last pages of the region
from map->start to map->start + map->size.

After kexec the new kernel reserves only the preserved pages, so the
last pages are released to the buddy allocator. But
reserve_mem_find_by_name() still returns the whole region including the
last pages, so they can be allocated while the subsystem is still using
them.

Preserve every page the region spans so the new kernel reserves all of
it.

Fixes: 8375b76517cb ("kho: replace kho_preserve_phys() with kho_preserve_pages()")
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
---

QEMU-based test results

- Booted with "memblock=debug kho=on reserve_mem=5000:64:oops"

  # kexec -s -l /bzImage --initrd=/initramfs.gz --reuse-cmdline
  # kexec -e
  # dmesg | grep kho_preserved_memory_reserve

1) AS-IS (before fix)
[    0.188536] __memblock_reserve: [0x000000013ffee000-0x000000013ffeefff] nid=-1 flags=0 kho_preserved_memory_reserve+0x3d/0x70

2) TO-BE (after fix)
[    0.076935] __memblock_reserve: [0x000000013ffee000-0x000000013ffeffff] nid=-1 flags=0 kho_preserved_memory_reserve+0x3d/0x70

 mm/memblock.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 777c69f05400..a17b1cccaf3d 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2534,7 +2534,8 @@ static int __init reserved_mem_preserve(void)
 	for (unsigned int i = 0; i < reserved_mem_count; i++, nr_preserved++) {
 		struct reserve_mem_table *map = &reserved_mem_table[i];
 		struct page *page = phys_to_page(map->start);
-		unsigned int nr_pages = map->size >> PAGE_SHIFT;
+		unsigned int nr_pages = PFN_UP(map->start + map->size) -
+					PFN_DOWN(map->start);
 
 		err = kho_preserve_pages(page, nr_pages);
 		if (err)
@@ -2547,7 +2548,8 @@ static int __init reserved_mem_preserve(void)
 	for (unsigned int i = 0; i < nr_preserved; i++) {
 		struct reserve_mem_table *map = &reserved_mem_table[i];
 		struct page *page = phys_to_page(map->start);
-		unsigned int nr_pages = map->size >> PAGE_SHIFT;
+		unsigned int nr_pages = PFN_UP(map->start + map->size) -
+					PFN_DOWN(map->start);
 
 		kho_unpreserve_pages(page, nr_pages);
 	}

base-commit: dde94c26af59f5020adafafa08ece21ccd32590b
-- 
2.43.0