memblock: make free_reserved_area() update memblock if ARCH_KEEP_MEMBLOCK=y

On architectures that keep memblock after boot, freeing of reserved memory
with free_reserved_area() is paired with an update of memblock arrays,
usually by a call to memblock_free().

Make free_reserved_area() directly update memblock.reserved when
ARCH_KEEP_MEMBLOCK is enabled.

Remove the now-redundant explicit memblock_free() call from
arm64::free_initmem() and the #ifdef CONFIG_ARCH_KEEP_MEMBLOCK block
from the generic free_initrd_mem().

Link: https://patch.msgid.link/20260323074836.3653702-8-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Author: rppt

arch/arm64/mm/init.c

@@ -385,9 +385,6 @@ void free_initmem(void)
 	WARN_ON(!IS_ALIGNED((unsigned long)lm_init_begin, PAGE_SIZE));
 	WARN_ON(!IS_ALIGNED((unsigned long)lm_init_end, PAGE_SIZE));
 
-	/* Delete __init region from memblock.reserved. */
-	memblock_free(lm_init_begin, lm_init_end - lm_init_begin);
-
 	free_reserved_area(lm_init_begin, lm_init_end,
 			   POISON_FREE_INITMEM, "unused kernel");
 	/*

init/initramfs.c

@@ -652,13 +652,6 @@ void __init reserve_initrd_mem(void)
 
 void __weak __init free_initrd_mem(unsigned long start, unsigned long end)
 {
-#ifdef CONFIG_ARCH_KEEP_MEMBLOCK
-	unsigned long aligned_start = ALIGN_DOWN(start, PAGE_SIZE);
-	unsigned long aligned_end = ALIGN(end, PAGE_SIZE);
-
-	memblock_free((void *)aligned_start, aligned_end - aligned_start);
-#endif
-
 	free_reserved_area((void *)start, (void *)end, POISON_FREE_INITMEM,
 			"initrd");
 }

mm/memblock.c

@@ -943,6 +943,12 @@ unsigned long free_reserved_area(void *start, void *end, int poison, const char
 		end_pa = __pa(end - 1) + 1;
 	}
 
+	if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
+		if (start_pa < end_pa)
+			memblock_remove_range(&memblock.reserved,
+					      start_pa, end_pa - start_pa);
+	}
+
 	pages = __free_reserved_area(start_pa, end_pa, poison);
 	if (pages && s)
 		pr_info("Freeing %s memory: %ldK\n", s, K(pages));