powerpc: Fix oops when echoing bad values to /sys/devices/system/memory/probe

If we echo an address the hypervisor doesn't like to
/sys/devices/system/memory/probe we oops the box:

# echo 0x10000000000 > /sys/devices/system/memory/probe

kernel BUG at arch/powerpc/mm/hash_utils_64.c:541!

The backtrace is:

create_section_mapping
arch_add_memory
add_memory
memory_probe_store
sysdev_class_store
sysfs_write_file
vfs_write
SyS_write

In create_section_mapping we BUG if htab_bolt_mapping returned
an error. A better approach is to return an error which will
propagate back to userspace.

Rerunning the test with this patch applied:

# echo 0x10000000000 > /sys/devices/system/memory/probe
-bash: echo: write error: Invalid argument
Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: stable@kernel.org
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/sparsemem.h

@@ -16,7 +16,7 @@
 #endif /* CONFIG_SPARSEMEM */
 
 #ifdef CONFIG_MEMORY_HOTPLUG
-extern void create_section_mapping(unsigned long start, unsigned long end);
+extern int create_section_mapping(unsigned long start, unsigned long end);
 extern int remove_section_mapping(unsigned long start, unsigned long end);
 #ifdef CONFIG_NUMA
 extern int hot_add_scn_to_nid(unsigned long scn_addr);

arch/powerpc/mm/hash_utils_64.c

@@ -531,11 +531,11 @@ static unsigned long __init htab_get_table_size(void)
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
-void create_section_mapping(unsigned long start, unsigned long end)
+int create_section_mapping(unsigned long start, unsigned long end)
 {
-	BUG_ON(htab_bolt_mapping(start, end, __pa(start),
+	return htab_bolt_mapping(start, end, __pa(start),
 				 pgprot_val(PAGE_KERNEL), mmu_linear_psize,
-				 mmu_kernel_ssize));
+				 mmu_kernel_ssize);
 }
 
 int remove_section_mapping(unsigned long start, unsigned long end)

arch/powerpc/mm/mem.c

@@ -123,7 +123,8 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	pgdata = NODE_DATA(nid);
 
 	start = (unsigned long)__va(start);
-	create_section_mapping(start, start + size);
+	if (create_section_mapping(start, start + size))
+		return -EINVAL;
 
 	/* this should work for most non-highmem platforms */
 	zone = pgdata->node_zones;