powerpc: fadump: pair alloc_pages_exact() with free_pages_exact()

fadump allocates buffers with alloc_pages_exact(), but then marks them
as reserved and frees using free_reserved_area().

This is completely unnecessary and the pages allocated with
alloc_pages_exact() can be naturally freed with free_pages_exact().

Replace freeing of memory in fadump_free_buffer() with
free_pages_exact() and simplify allocation code so that it won't mark
allocated pages as reserved.

Link: https://patch.msgid.link/20260323074836.3653702-3-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Author: rppt

arch/powerpc/kernel/fadump.c

@@ -775,24 +775,12 @@ void __init fadump_update_elfcore_header(char *bufp)
 
 static void *__init fadump_alloc_buffer(unsigned long size)
 {
-	unsigned long count, i;
-	struct page *page;
-	void *vaddr;
-
-	vaddr = alloc_pages_exact(size, GFP_KERNEL | __GFP_ZERO);
-	if (!vaddr)
-		return NULL;
-
-	count = PAGE_ALIGN(size) / PAGE_SIZE;
-	page = virt_to_page(vaddr);
-	for (i = 0; i < count; i++)
-		mark_page_reserved(page + i);
-	return vaddr;
+	return  alloc_pages_exact(size, GFP_KERNEL | __GFP_ZERO);
 }
 
 static void fadump_free_buffer(unsigned long vaddr, unsigned long size)
 {
-	free_reserved_area((void *)vaddr, (void *)(vaddr + size), -1, NULL);
+	free_pages_exact((void *)vaddr, size);
 }
 
 s32 __init fadump_setup_cpu_notes_buf(u32 num_cpus)