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

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

Until commit cddb5dd ("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: cddb5dd ("arm, xtensa: simplify initialization of high memory pages")
Link: https://lore.kernel.org/r/20201029110334.4118-1-ardb@kernel.org/
Link: https://lore.kernel.org/r/20201031094345.6984-1-rppt@kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Co-developed-by:  Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>

Author: ardbiesheuvel

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)

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)