1 files changed, 80 insertions, 110 deletions

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index e000fa3b9f..0e7427c2ba 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -25,6 +25,7 @@
 #include <linux/notifier.h>
 #include <linux/percpu_counter.h>
 #include <linux/page_reporting.h>
+#include <linux/sizes.h>
 
 #include <linux/hyperv.h>
 #include <asm/hyperv-tlfs.h>
@@ -41,8 +42,6 @@
  * Begin protocol definitions.
  */
 
-
-
 /*
  * Protocol versions. The low word is the minor version, the high word the major
  * version.
@@ -71,8 +70,6 @@ enum {
 	DYNMEM_PROTOCOL_VERSION_CURRENT = DYNMEM_PROTOCOL_VERSION_WIN10
 };
 
-
-
 /*
  * Message Types
  */
@@ -101,7 +98,6 @@ enum dm_message_type {
 	DM_VERSION_1_MAX		= 12
 };
 
-
 /*
  * Structures defining the dynamic memory management
  * protocol.
@@ -115,7 +111,6 @@ union dm_version {
 	__u32 version;
 } __packed;
 
-
 union dm_caps {
 	struct {
 		__u64 balloon:1;
@@ -148,8 +143,6 @@ union dm_mem_page_range {
 	__u64  page_range;
 } __packed;
 
-
-
 /*
  * The header for all dynamic memory messages:
  *
@@ -174,7 +167,6 @@ struct dm_message {
 	__u8 data[]; /* enclosed message */
 } __packed;
 
-
 /*
  * Specific message types supporting the dynamic memory protocol.
  */
@@ -271,7 +263,6 @@ struct dm_status {
 	__u32 io_diff;
 } __packed;
 
-
 /*
  * Message to ask the guest to allocate memory - balloon up message.
  * This message is sent from the host to the guest. The guest may not be
@@ -286,14 +277,13 @@ struct dm_balloon {
 	__u32 reservedz;
 } __packed;
 
-
 /*
  * Balloon response message; this message is sent from the guest
  * to the host in response to the balloon message.
  *
  * reservedz: Reserved; must be set to zero.
  * more_pages: If FALSE, this is the last message of the transaction.
- * if TRUE there will atleast one more message from the guest.
+ * if TRUE there will be at least one more message from the guest.
  *
  * range_count: The number of ranges in the range array.
  *
@@ -314,7 +304,7 @@ struct dm_balloon_response {
  * to the guest to give guest more memory.
  *
  * more_pages: If FALSE, this is the last message of the transaction.
- * if TRUE there will atleast one more message from the guest.
+ * if TRUE there will be at least one more message from the guest.
  *
  * reservedz: Reserved; must be set to zero.
  *
@@ -342,7 +332,6 @@ struct dm_unballoon_response {
 	struct dm_header hdr;
 } __packed;
 
-
 /*
  * Hot add request message. Message sent from the host to the guest.
  *
@@ -390,7 +379,6 @@ enum dm_info_type {
 	MAX_INFO_TYPE
 };
 
-
 /*
  * Header for the information message.
  */
@@ -425,11 +413,11 @@ struct dm_info_msg {
  * The range start_pfn : end_pfn specifies the range
  * that the host has asked us to hot add. The range
  * start_pfn : ha_end_pfn specifies the range that we have
- * currently hot added. We hot add in multiples of 128M
- * chunks; it is possible that we may not be able to bring
- * online all the pages in the region. The range
+ * currently hot added. We hot add in chunks equal to the
+ * memory block size; it is possible that we may not be able
+ * to bring online all the pages in the region. The range
  * covered_start_pfn:covered_end_pfn defines the pages that can
- * be brough online.
+ * be brought online.
  */
 
 struct hv_hotadd_state {
@@ -480,10 +468,10 @@ static unsigned long last_post_time;
 
 static int hv_hypercall_multi_failure;
 
-module_param(hot_add, bool, (S_IRUGO | S_IWUSR));
+module_param(hot_add, bool, 0644);
 MODULE_PARM_DESC(hot_add, "If set attempt memory hot_add");
 
-module_param(pressure_report_delay, uint, (S_IRUGO | S_IWUSR));
+module_param(pressure_report_delay, uint, 0644);
 MODULE_PARM_DESC(pressure_report_delay, "Delay in secs in reporting pressure");
 static atomic_t trans_id = ATOMIC_INIT(0);
 
@@ -502,11 +490,13 @@ enum hv_dm_state {
 	DM_INIT_ERROR
 };
 
-
 static __u8 recv_buffer[HV_HYP_PAGE_SIZE];
 static __u8 balloon_up_send_buffer[HV_HYP_PAGE_SIZE];
+
+static unsigned long ha_pages_in_chunk;
+#define HA_BYTES_IN_CHUNK (ha_pages_in_chunk << PAGE_SHIFT)
+
 #define PAGES_IN_2M (2 * 1024 * 1024 / PAGE_SIZE)
-#define HA_CHUNK (128 * 1024 * 1024 / PAGE_SIZE)
 
 struct hv_dynmem_device {
 	struct hv_device *dev;
@@ -595,12 +585,12 @@ static inline bool has_pfn_is_backed(struct hv_hotadd_state *has,
 	struct hv_hotadd_gap *gap;
 
 	/* The page is not backed. */
-	if ((pfn < has->covered_start_pfn) || (pfn >= has->covered_end_pfn))
+	if (pfn < has->covered_start_pfn || pfn >= has->covered_end_pfn)
 		return false;
 
 	/* Check for gaps. */
 	list_for_each_entry(gap, &has->gap_list, list) {
-		if ((pfn >= gap->start_pfn) && (pfn < gap->end_pfn))
+		if (pfn >= gap->start_pfn && pfn < gap->end_pfn)
 			return false;
 	}
 
@@ -724,28 +714,21 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
 	unsigned long processed_pfn;
 	unsigned long total_pfn = pfn_count;
 
-	for (i = 0; i < (size/HA_CHUNK); i++) {
-		start_pfn = start + (i * HA_CHUNK);
+	for (i = 0; i < (size/ha_pages_in_chunk); i++) {
+		start_pfn = start + (i * ha_pages_in_chunk);
 
 		scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
-			has->ha_end_pfn +=  HA_CHUNK;
-
-			if (total_pfn > HA_CHUNK) {
-				processed_pfn = HA_CHUNK;
-				total_pfn -= HA_CHUNK;
-			} else {
-				processed_pfn = total_pfn;
-				total_pfn = 0;
-			}
-
-			has->covered_end_pfn +=  processed_pfn;
+			has->ha_end_pfn += ha_pages_in_chunk;
+			processed_pfn = umin(total_pfn, ha_pages_in_chunk);
+			total_pfn -= processed_pfn;
+			has->covered_end_pfn += processed_pfn;
 		}
 
 		reinit_completion(&dm_device.ol_waitevent);
 
 		nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
 		ret = add_memory(nid, PFN_PHYS((start_pfn)),
-				(HA_CHUNK << PAGE_SHIFT), MHP_MERGE_RESOURCE);
+				 HA_BYTES_IN_CHUNK, MHP_MERGE_RESOURCE);
 
 		if (ret) {
 			pr_err("hot_add memory failed error is %d\n", ret);
@@ -760,7 +743,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
 				do_hot_add = false;
 			}
 			scoped_guard(spinlock_irqsave, &dm_device.ha_lock) {
-				has->ha_end_pfn -= HA_CHUNK;
+				has->ha_end_pfn -= ha_pages_in_chunk;
 				has->covered_end_pfn -=  processed_pfn;
 			}
 			break;
@@ -787,8 +770,8 @@ static void hv_online_page(struct page *pg, unsigned int order)
 	guard(spinlock_irqsave)(&dm_device.ha_lock);
 	list_for_each_entry(has, &dm_device.ha_region_list, list) {
 		/* The page belongs to a different HAS. */
-		if ((pfn < has->start_pfn) ||
-				(pfn + (1UL << order) > has->end_pfn))
+		if (pfn < has->start_pfn ||
+		    (pfn + (1UL << order) > has->end_pfn))
 			continue;
 
 		hv_bring_pgs_online(has, pfn, 1UL << order);
@@ -800,7 +783,7 @@ static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)
 {
 	struct hv_hotadd_state *has;
 	struct hv_hotadd_gap *gap;
-	unsigned long residual, new_inc;
+	unsigned long residual;
 	int ret = 0;
 
 	guard(spinlock_irqsave)(&dm_device.ha_lock);
@@ -836,15 +819,9 @@ static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)
 		 * our current limit; extend it.
 		 */
 		if ((start_pfn + pfn_cnt) > has->end_pfn) {
+			/* Extend the region by multiples of ha_pages_in_chunk */
 			residual = (start_pfn + pfn_cnt - has->end_pfn);
-			/*
-			 * Extend the region by multiples of HA_CHUNK.
-			 */
-			new_inc = (residual / HA_CHUNK) * HA_CHUNK;
-			if (residual % HA_CHUNK)
-				new_inc += HA_CHUNK;
-
-			has->end_pfn += new_inc;
+			has->end_pfn += ALIGN(residual, ha_pages_in_chunk);
 		}
 
 		ret = 1;
@@ -855,7 +832,7 @@ static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)
 }
 
 static unsigned long handle_pg_range(unsigned long pg_start,
-					unsigned long pg_count)
+				     unsigned long pg_count)
 {
 	unsigned long start_pfn = pg_start;
 	unsigned long pfn_cnt = pg_count;
@@ -866,7 +843,7 @@ static unsigned long handle_pg_range(unsigned long pg_start,
 	unsigned long res = 0, flags;
 
 	pr_debug("Hot adding %lu pages starting at pfn 0x%lx.\n", pg_count,
-		pg_start);
+		 pg_start);
 
 	spin_lock_irqsave(&dm_device.ha_lock, flags);
 	list_for_each_entry(has, &dm_device.ha_region_list, list) {
@@ -902,22 +879,19 @@ static unsigned long handle_pg_range(unsigned long pg_start,
 			if (start_pfn > has->start_pfn &&
 			    online_section_nr(pfn_to_section_nr(start_pfn)))
 				hv_bring_pgs_online(has, start_pfn, pgs_ol);
-
 		}
 
-		if ((has->ha_end_pfn < has->end_pfn) && (pfn_cnt > 0)) {
+		if (has->ha_end_pfn < has->end_pfn && pfn_cnt > 0) {
 			/*
 			 * We have some residual hot add range
 			 * that needs to be hot added; hot add
 			 * it now. Hot add a multiple of
-			 * HA_CHUNK that fully covers the pages
+			 * ha_pages_in_chunk that fully covers the pages
 			 * we have.
 			 */
 			size = (has->end_pfn - has->ha_end_pfn);
 			if (pfn_cnt <= size) {
-				size = ((pfn_cnt / HA_CHUNK) * HA_CHUNK);
-				if (pfn_cnt % HA_CHUNK)
-					size += HA_CHUNK;
+				size = ALIGN(pfn_cnt, ha_pages_in_chunk);
 			} else {
 				pfn_cnt = size;
 			}
@@ -1010,10 +984,7 @@ static void hot_add_req(struct work_struct *dummy)
 	rg_start = dm->ha_wrk.ha_region_range.finfo.start_page;
 	rg_sz = dm->ha_wrk.ha_region_range.finfo.page_cnt;
 
-	if ((rg_start == 0) && (!dm->host_specified_ha_region)) {
-		unsigned long region_size;
-		unsigned long region_start;
-
+	if (rg_start == 0 && !dm->host_specified_ha_region) {
 		/*
 		 * The host has not specified the hot-add region.
 		 * Based on the hot-add page range being specified,
@@ -1021,19 +992,13 @@ static void hot_add_req(struct work_struct *dummy)
 		 * that need to be hot-added while ensuring the alignment
 		 * and size requirements of Linux as it relates to hot-add.
 		 */
-		region_size = (pfn_cnt / HA_CHUNK) * HA_CHUNK;
-		if (pfn_cnt % HA_CHUNK)
-			region_size += HA_CHUNK;
-
-		region_start = (pg_start / HA_CHUNK) * HA_CHUNK;
-
-		rg_start = region_start;
-		rg_sz = region_size;
+		rg_start = ALIGN_DOWN(pg_start, ha_pages_in_chunk);
+		rg_sz = ALIGN(pfn_cnt, ha_pages_in_chunk);
 	}
 
 	if (do_hot_add)
 		resp.page_count = process_hot_add(pg_start, pfn_cnt,
-						rg_start, rg_sz);
+						  rg_start, rg_sz);
 
 	dm->num_pages_added += resp.page_count;
 #endif
@@ -1211,11 +1176,10 @@ static void post_status(struct hv_dynmem_device *dm)
 				sizeof(struct dm_status),
 				(unsigned long)NULL,
 				VM_PKT_DATA_INBAND, 0);
-
 }
 
 static void free_balloon_pages(struct hv_dynmem_device *dm,
-			 union dm_mem_page_range *range_array)
+			       union dm_mem_page_range *range_array)
 {
 	int num_pages = range_array->finfo.page_cnt;
 	__u64 start_frame = range_array->finfo.start_page;
@@ -1231,8 +1195,6 @@ static void free_balloon_pages(struct hv_dynmem_device *dm,
 	}
 }
 
-
-
 static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
 					unsigned int num_pages,
 					struct dm_balloon_response *bl_resp,
@@ -1278,7 +1240,6 @@ static unsigned int alloc_balloon_pages(struct hv_dynmem_device *dm,
 			page_to_pfn(pg);
 		bl_resp->range_array[i].finfo.page_cnt = alloc_unit;
 		bl_resp->hdr.size += sizeof(union dm_mem_page_range);
-
 	}
 
 	return i * alloc_unit;
@@ -1332,7 +1293,7 @@ static void balloon_up(struct work_struct *dummy)
 
 		if (num_ballooned == 0 || num_ballooned == num_pages) {
 			pr_debug("Ballooned %u out of %u requested pages.\n",
-				num_pages, dm_device.balloon_wrk.num_pages);
+				 num_pages, dm_device.balloon_wrk.num_pages);
 
 			bl_resp->more_pages = 0;
 			done = true;
@@ -1366,16 +1327,15 @@ static void balloon_up(struct work_struct *dummy)
 
 			for (i = 0; i < bl_resp->range_count; i++)
 				free_balloon_pages(&dm_device,
-						 &bl_resp->range_array[i]);
+						   &bl_resp->range_array[i]);
 
 			done = true;
 		}
 	}
-
 }
 
 static void balloon_down(struct hv_dynmem_device *dm,
-			struct dm_unballoon_request *req)
+			 struct dm_unballoon_request *req)
 {
 	union dm_mem_page_range *range_array = req->range_array;
 	int range_count = req->range_count;
@@ -1389,7 +1349,7 @@ static void balloon_down(struct hv_dynmem_device *dm,
 	}
 
 	pr_debug("Freed %u ballooned pages.\n",
-		prev_pages_ballooned - dm->num_pages_ballooned);
+		 prev_pages_ballooned - dm->num_pages_ballooned);
 
 	if (req->more_pages == 1)
 		return;
@@ -1414,8 +1374,7 @@ static int dm_thread_func(void *dm_dev)
 	struct hv_dynmem_device *dm = dm_dev;
 
 	while (!kthread_should_stop()) {
-		wait_for_completion_interruptible_timeout(
-						&dm_device.config_event, 1*HZ);
+		wait_for_completion_interruptible_timeout(&dm_device.config_event, 1 * HZ);
 		/*
 		 * The host expects us to post information on the memory
 		 * pressure every second.
@@ -1439,9 +1398,8 @@ static int dm_thread_func(void *dm_dev)
 	return 0;
 }
 
-
 static void version_resp(struct hv_dynmem_device *dm,
-			struct dm_version_response *vresp)
+			 struct dm_version_response *vresp)
 {
 	struct dm_version_request version_req;
 	int ret;
@@ -1502,7 +1460,7 @@ version_error:
 }
 
 static void cap_resp(struct hv_dynmem_device *dm,
-			struct dm_capabilities_resp_msg *cap_resp)
+		     struct dm_capabilities_resp_msg *cap_resp)
 {
 	if (!cap_resp->is_accepted) {
 		pr_err("Capabilities not accepted by host\n");
@@ -1535,7 +1493,7 @@ static void balloon_onchannelcallback(void *context)
 		switch (dm_hdr->type) {
 		case DM_VERSION_RESPONSE:
 			version_resp(dm,
-				 (struct dm_version_response *)dm_msg);
+				     (struct dm_version_response *)dm_msg);
 			break;
 
 		case DM_CAPABILITIES_RESPONSE:
@@ -1565,7 +1523,7 @@ static void balloon_onchannelcallback(void *context)
 
 			dm->state = DM_BALLOON_DOWN;
 			balloon_down(dm,
-				 (struct dm_unballoon_request *)recv_buffer);
+				     (struct dm_unballoon_request *)recv_buffer);
 			break;
 
 		case DM_MEM_HOT_ADD_REQUEST:
@@ -1603,17 +1561,15 @@ static void balloon_onchannelcallback(void *context)
 
 		default:
 			pr_warn_ratelimited("Unhandled message: type: %d\n", dm_hdr->type);
-
 		}
 	}
-
 }
 
 #define HV_LARGE_REPORTING_ORDER	9
 #define HV_LARGE_REPORTING_LEN (HV_HYP_PAGE_SIZE << \
 		HV_LARGE_REPORTING_ORDER)
 static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
-		    struct scatterlist *sgl, unsigned int nents)
+			       struct scatterlist *sgl, unsigned int nents)
 {
 	unsigned long flags;
 	struct hv_memory_hint *hint;
@@ -1648,7 +1604,7 @@ static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
 		 */
 
 		/* page reporting for pages 2MB or higher */
-		if (order >= HV_LARGE_REPORTING_ORDER ) {
+		if (order >= HV_LARGE_REPORTING_ORDER) {
 			range->page.largepage = 1;
 			range->page_size = HV_GPA_PAGE_RANGE_PAGE_SIZE_2MB;
 			range->base_large_pfn = page_to_hvpfn(
@@ -1662,23 +1618,21 @@ static int hv_free_page_report(struct page_reporting_dev_info *pr_dev_info,
 			range->page.additional_pages =
 				(sg->length / HV_HYP_PAGE_SIZE) - 1;
 		}
-
 	}
 
 	status = hv_do_rep_hypercall(HV_EXT_CALL_MEMORY_HEAT_HINT, nents, 0,
 				     hint, NULL);
 	local_irq_restore(flags);
 	if (!hv_result_success(status)) {
-
 		pr_err("Cold memory discard hypercall failed with status %llx\n",
-				status);
+		       status);
 		if (hv_hypercall_multi_failure > 0)
 			hv_hypercall_multi_failure++;
 
 		if (hv_result(status) == HV_STATUS_INVALID_PARAMETER) {
 			pr_err("Underlying Hyper-V does not support order less than 9. Hypercall failed\n");
 			pr_err("Defaulting to page_reporting_order %d\n",
-					pageblock_order);
+			       pageblock_order);
 			page_reporting_order = pageblock_order;
 			hv_hypercall_multi_failure++;
 			return -EINVAL;
@@ -1712,7 +1666,7 @@ static void enable_page_reporting(void)
 		pr_err("Failed to enable cold memory discard: %d\n", ret);
 	} else {
 		pr_info("Cold memory discard hint enabled with order %d\n",
-				page_reporting_order);
+			page_reporting_order);
 	}
 }
 
@@ -1795,7 +1749,7 @@ static int balloon_connect_vsp(struct hv_device *dev)
 	if (ret)
 		goto out;
 
-	t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
+	t = wait_for_completion_timeout(&dm_device.host_event, 5 * HZ);
 	if (t == 0) {
 		ret = -ETIMEDOUT;
 		goto out;
@@ -1831,10 +1785,13 @@ static int balloon_connect_vsp(struct hv_device *dev)
 	cap_msg.caps.cap_bits.hot_add = hot_add_enabled();
 
 	/*
-	 * Specify our alignment requirements as it relates
-	 * memory hot-add. Specify 128MB alignment.
+	 * Specify our alignment requirements for memory hot-add. The value is
+	 * the log base 2 of the number of megabytes in a chunk. For example,
+	 * with 256 MiB chunks, the value is 8. The number of MiB in a chunk
+	 * must be a power of 2.
 	 */
-	cap_msg.caps.cap_bits.hot_add_alignment = 7;
+	cap_msg.caps.cap_bits.hot_add_alignment =
+					ilog2(HA_BYTES_IN_CHUNK / SZ_1M);
 
 	/*
 	 * Currently the host does not use these
@@ -1850,7 +1807,7 @@ static int balloon_connect_vsp(struct hv_device *dev)
 	if (ret)
 		goto out;
 
-	t = wait_for_completion_timeout(&dm_device.host_event, 5*HZ);
+	t = wait_for_completion_timeout(&dm_device.host_event, 5 * HZ);
 	if (t == 0) {
 		ret = -ETIMEDOUT;
 		goto out;
@@ -1891,8 +1848,8 @@ static int hv_balloon_debug_show(struct seq_file *f, void *offset)
 	char *sname;
 
 	seq_printf(f, "%-22s: %u.%u\n", "host_version",
-				DYNMEM_MAJOR_VERSION(dm->version),
-				DYNMEM_MINOR_VERSION(dm->version));
+			DYNMEM_MAJOR_VERSION(dm->version),
+			DYNMEM_MINOR_VERSION(dm->version));
 
 	seq_printf(f, "%-22s:", "capabilities");
 	if (ballooning_enabled())
@@ -1941,10 +1898,10 @@ static int hv_balloon_debug_show(struct seq_file *f, void *offset)
 	seq_printf(f, "%-22s: %u\n", "pages_ballooned", dm->num_pages_ballooned);
 
 	seq_printf(f, "%-22s: %lu\n", "total_pages_committed",
-				get_pages_committed(dm));
+		   get_pages_committed(dm));
 
 	seq_printf(f, "%-22s: %llu\n", "max_dynamic_page_count",
-				dm->max_dynamic_page_count);
+		   dm->max_dynamic_page_count);
 
 	return 0;
 }
@@ -1954,7 +1911,7 @@ DEFINE_SHOW_ATTRIBUTE(hv_balloon_debug);
 static void  hv_balloon_debugfs_init(struct hv_dynmem_device *b)
 {
 	debugfs_create_file("hv-balloon", 0444, NULL, b,
-			&hv_balloon_debug_fops);
+			    &hv_balloon_debug_fops);
 }
 
 static void  hv_balloon_debugfs_exit(struct hv_dynmem_device *b)
@@ -1984,8 +1941,23 @@ static int balloon_probe(struct hv_device *dev,
 		hot_add = false;
 
 #ifdef CONFIG_MEMORY_HOTPLUG
+	/*
+	 * Hot-add must operate in chunks that are of size equal to the
+	 * memory block size because that's what the core add_memory()
+	 * interface requires. The Hyper-V interface requires that the memory
+	 * block size be a power of 2, which is guaranteed by the check in
+	 * memory_dev_init().
+	 */
+	ha_pages_in_chunk = memory_block_size_bytes() / PAGE_SIZE;
 	do_hot_add = hot_add;
 #else
+	/*
+	 * Without MEMORY_HOTPLUG, the guest returns a failure status for all
+	 * hot add requests from Hyper-V, and the chunk size is used only to
+	 * specify alignment to Hyper-V as required by the host/guest protocol.
+	 * Somewhat arbitrarily, use 128 MiB.
+	 */
+	ha_pages_in_chunk = SZ_128M / PAGE_SIZE;
 	do_hot_add = false;
 #endif
 	dm_device.dev = dev;
@@ -2097,7 +2069,6 @@ static int balloon_suspend(struct hv_device *hv_dev)
 	tasklet_enable(&hv_dev->channel->callback_event);
 
 	return 0;
-
 }
 
 static int balloon_resume(struct hv_device *dev)
@@ -2156,7 +2127,6 @@ static  struct hv_driver balloon_drv = {
 
 static int __init init_balloon_drv(void)
 {
-
 	return vmbus_driver_register(&balloon_drv);
 }