fadump: Move fadump_cma_init after initmem_init

During early init CMA_MIN_ALIGNMENT_BYTES can be PAGE_SIZE,
since pageblock_order is still zero and it gets initialized
later during initmem_init() e.g.
setup_arch() -> initmem_init() -> sparse_init() -> set_pageblock_order()

One such use case is where this causes issues is -
early_setup() -> early_init_devtree() -> fadump_reserve_mem() -> fadump_cma_init()

This causes CMA memory alignment check to be bypassed in
cma_init_reserved_mem(). Then later cma_activate_area() can hit
a VM_BUG_ON_PAGE(pfn & ((1 << order) - 1)) if the reserved memory
area was not pageblock_order aligned.

Fix it by moving the call to fadump_cma_init() after initmem_init(),
where other such cma reservations also gets called.

<stack trace>
==============
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10010
flags: 0x13ffff800000000(node=1|zone=0|lastcpupid=0x7ffff) CMA
raw: 013ffff800000000 5deadbeef0000100 5deadbeef0000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: VM_BUG_ON_PAGE(pfn & ((1 << order) - 1))
------------[ cut here ]------------
kernel BUG at mm/page_alloc.c:778!

Call Trace:
__free_one_page+0x57c/0x7b0 (unreliable)
free_pcppages_bulk+0x1a8/0x2c8
free_unref_page_commit+0x3d4/0x4e4
free_unref_page+0x458/0x6d0
init_cma_reserved_pageblock+0x114/0x198
cma_init_reserved_areas+0x270/0x3e0
do_one_initcall+0x80/0x2f8
kernel_init_freeable+0x33c/0x530
kernel_init+0x34/0x26c
ret_from_kernel_user_thread+0x14/0x1c

Suggested-by: David Hildenbrand <[email protected]>
Reported-by: Sachin P Bappalige <[email protected]>
Signed-off-by: Ritesh Harjani (IBM) <[email protected]>

arch/powerpc/include/asm/fadump.h

@@ -34,4 +34,11 @@ extern int early_init_dt_scan_fw_dump(unsigned long node, const char *uname,
 				      int depth, void *data);
 extern int fadump_reserve_mem(void);
 #endif
+
+#if defined(CONFIG_FA_DUMP) && defined(CONFIG_CMA)
+void fadump_cma_init(void);
+#else
+void fadump_cma_init(void) { }
+#endif
+
 #endif /* _ASM_POWERPC_FADUMP_H */

arch/powerpc/kernel/fadump.c

@@ -78,7 +78,7 @@ static struct cma *fadump_cma;
  * But for some reason even if it fails we still have the memory reservation
  * with us and we can still continue doing fadump.
  */
-static void __init fadump_cma_init(void)
+void __init fadump_cma_init(void)
 {
 	unsigned long long base, size, end;
 	int rc;
@@ -141,8 +141,6 @@ static void __init fadump_cma_init(void)
 		fw_dump.boot_memory_size >> 20);
 	return;
 }
-#else
-static void __init fadump_cma_init(void) { }
 #endif /* CONFIG_CMA */
 
 /*
@@ -644,8 +642,6 @@ int __init fadump_reserve_mem(void)
 
 		pr_info("Reserved %lldMB of memory at %#016llx (System RAM: %lldMB)\n",
 			(size >> 20), base, (memblock_phys_mem_size() >> 20));
-
-		fadump_cma_init();
 	}
 
 	return ret;

arch/powerpc/kernel/setup-common.c

@@ -997,9 +997,11 @@ void __init setup_arch(char **cmdline_p)
 	initmem_init();
 
 	/*
-	 * Reserve large chunks of memory for use by CMA for KVM and hugetlb. These must
-	 * be called after initmem_init(), so that pageblock_order is initialised.
+	 * Reserve large chunks of memory for use by CMA for fadump, KVM and
+	 * hugetlb. These must be called after initmem_init(), so that
+	 * pageblock_order is initialised.
 	 */
+	fadump_cma_init();
 	kvm_cma_reserve();
 	gigantic_hugetlb_cma_reserve();