arm64: Fix DMAP handling in arm64_get_writable_addr()

PHYS_TO_DMAP_PAGE expects a page-aligned physical address.

Author: markjdb

sys/arm64/arm64/machdep.c

@@ -465,7 +465,8 @@ arm64_get_writable_addr(void *addr, void **out)
 	 * If it is within the DMAP region and is writable use that.
 	 */
 	if (PHYS_IN_DMAP_RANGE(pa)) {
-		addr = (void *)PHYS_TO_DMAP_PAGE(pa);
+		addr = (void *)((uintptr_t)PHYS_TO_DMAP_PAGE(trunc_page(pa)) +
+		    ((vm_offset_t)addr & PAGE_MASK));
 		if (PAR_SUCCESS(arm64_address_translate_s1e1w(
 		    (vm_offset_t)addr))) {
 			*out = addr;