stm class: Use vmalloc for the master map

Fengguang is running into a warning from the buddy allocator:

> swapper/0: page allocation failure: order:9, mode:0x14040c0(GFP_KERNEL|__GFP_COMP), nodemask=(null)
> CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.17.0-rc1 #262
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> Call Trace:
...
>  __kmalloc+0x14b/0x180: ____cache_alloc at mm/slab.c:3127
>  stm_register_device+0xf3/0x5c0: stm_register_device at drivers/hwtracing/stm/core.c:695
...

Which is basically a result of the stm class trying to allocate ~512kB
for the dummy_stm with its default parameters. There's no reason, however,
for it not to be vmalloc()ed instead, which is what this patch does.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NAlexander Shishkin <alexander.shishkin@linux.intel.com>
CC: stable@vger.kernel.org # v4.4+
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/stm/core.c

@@ -674,7 +674,7 @@ static void stm_device_release(struct device *dev)
 {
 	struct stm_device *stm = to_stm_device(dev);
 
-	kfree(stm);
+	vfree(stm);
 }
 
 int stm_register_device(struct device *parent, struct stm_data *stm_data,
@@ -691,7 +691,7 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 		return -EINVAL;
 
 	nmasters = stm_data->sw_end - stm_data->sw_start + 1;
-	stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
+	stm = vzalloc(sizeof(*stm) + nmasters * sizeof(void *));
 	if (!stm)
 		return -ENOMEM;
 
@@ -744,7 +744,7 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 	/* matches device_initialize() above */
 	put_device(&stm->dev);
 err_free:
-	kfree(stm);
+	vfree(stm);
 
 	return err;
 }