[PATCH] ARM, xtensa: highmem: avoid clobbering non-page aligned memory reservations

[Mike Rapoport]

From: Ard Biesheuvel <ardb@xxxxxxxxxx>

free_highpages() iterates over the free memblock regions in high
memory, and marks each page as available for the memory management
system.

Until commit cddb5ddf2b76 ("arm, xtensa: simplify initialization of
high memory pages") it rounded beginning of each region upwards and end of
each region downwards.

However, after that commit free_highmem() rounds the beginning and end of
each region downwards, and we may end up freeing a page that is
memblock_reserve()d, resulting in memory corruption.

Restore the original rounding of the region boundaries to avoid freeing
reserved pages.

Fixes: cddb5ddf2b76 ("arm, xtensa: simplify initialization of high memory pages")
Link: https://lore.kernel.org/r/20201029110334.4118-1-ardb@xxxxxxxxxx/
Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
Co-developed-by:  Mike Rapoport <rppt@xxxxxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---

Max, Russell,

Please let me know how do you prefer to take it upstream.
If needed this can go via memblock tree.

v2: fix words order in the commit message

 arch/arm/mm/init.c    | 4 ++--
 arch/xtensa/mm/init.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index d57112a276f5..c23dbf8bebee 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -354,8 +354,8 @@ static void __init free_highpages(void)
 	/* set highmem page free */
 	for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE,
 				&range_start, &range_end, NULL) {
-		unsigned long start = PHYS_PFN(range_start);
-		unsigned long end = PHYS_PFN(range_end);
+		unsigned long start = PFN_UP(range_start);
+		unsigned long end = PFN_DOWN(range_end);
 
 		/* Ignore complete lowmem entries */
 		if (end <= max_low)
diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index c6fc83efee0c..8731b7ad9308 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -89,8 +89,8 @@ static void __init free_highpages(void)
 	/* set highmem page free */
 	for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE,
 				&range_start, &range_end, NULL) {
-		unsigned long start = PHYS_PFN(range_start);
-		unsigned long end = PHYS_PFN(range_end);
+		unsigned long start = PFN_UP(range_start);
+		unsigned long end = PFN_DOWN(range_end);
 
 		/* Ignore complete lowmem entries */
 		if (end <= max_low)
-- 
2.28.0