[PATCH 1/2] Drivers: hv: vmbus: Cleanup hv_post_message()

["K. Y. Srinivasan" <kys@microsoft.com>]

Minimize failures in this function by pre-allocating the buffer
for posting messages. The hypercall for posting the message can fail
for a number of reasons:

        1. Transient resource related issues
        2. Buffer alignment
        3. Buffer cannot span a page boundry

We address issues 2 and 3 by preallocating a per-cpu page for the buffer.
Transient resource related failures are handled by retrying by the callers
of this function.

This patch is based on the investigation
done by Dexuan Cui <decui@microsoft.com>.

I would like to thank Sitsofe Wheeler <sitsofe@yahoo.com>
for reporting the issue and helping in debuggging.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Cc: <stable@vger.kernel.org>
---
 drivers/hv/hv.c           |   27 +++++++++++++++------------
 drivers/hv/hyperv_vmbus.h |    4 ++++
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index edfc848..3e4235c 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -138,6 +138,8 @@ int hv_init(void)
 	memset(hv_context.synic_event_page, 0, sizeof(void *) * NR_CPUS);
 	memset(hv_context.synic_message_page, 0,
 	       sizeof(void *) * NR_CPUS);
+	memset(hv_context.post_msg_page, 0,
+	       sizeof(void *) * NR_CPUS);
 	memset(hv_context.vp_index, 0,
 	       sizeof(int) * NR_CPUS);
 	memset(hv_context.event_dpc, 0,
@@ -217,26 +219,18 @@ int hv_post_message(union hv_connection_id connection_id,
 		  enum hv_message_type message_type,
 		  void *payload, size_t payload_size)
 {
-	struct aligned_input {
-		u64 alignment8;
-		struct hv_input_post_message msg;
-	};
 
 	struct hv_input_post_message *aligned_msg;
 	u16 status;
-	unsigned long addr;
 
 	if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT)
 		return -EMSGSIZE;
 
-	addr = (unsigned long)kmalloc(sizeof(struct aligned_input), GFP_ATOMIC);
-	if (!addr)
-		return -ENOMEM;
-
 	aligned_msg = (struct hv_input_post_message *)
-			(ALIGN(addr, HV_HYPERCALL_PARAM_ALIGN));
+			hv_context.post_msg_page[get_cpu()];
 
 	aligned_msg->connectionid = connection_id;
+	aligned_msg->reserved = 0;
 	aligned_msg->message_type = message_type;
 	aligned_msg->payload_size = payload_size;
 	memcpy((void *)aligned_msg->payload, payload, payload_size);
@@ -244,8 +238,7 @@ int hv_post_message(union hv_connection_id connection_id,
 	status = do_hypercall(HVCALL_POST_MESSAGE, aligned_msg, NULL)
 		& 0xFFFF;
 
-	kfree((void *)addr);
-
+	put_cpu();
 	return status;
 }
 
@@ -294,6 +287,14 @@ int hv_synic_alloc(void)
 			pr_err("Unable to allocate SYNIC event page\n");
 			goto err;
 		}
+
+		hv_context.post_msg_page[cpu] =
+			(void *)get_zeroed_page(GFP_ATOMIC);
+
+		if (hv_context.post_msg_page[cpu] == NULL) {
+			pr_err("Unable to allocate post msg page\n");
+			goto err;
+		}
 	}
 
 	return 0;
@@ -308,6 +309,8 @@ static void hv_synic_free_cpu(int cpu)
 		free_page((unsigned long)hv_context.synic_event_page[cpu]);
 	if (hv_context.synic_message_page[cpu])
 		free_page((unsigned long)hv_context.synic_message_page[cpu]);
+	if (hv_context.post_msg_page[cpu])
+		free_page((unsigned long)hv_context.post_msg_page[cpu]);
 }
 
 void hv_synic_free(void)
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 22b7507..c386d8d 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -515,6 +515,10 @@ struct hv_context {
 	 * per-cpu list of the channels based on their CPU affinity.
 	 */
 	struct list_head percpu_list[NR_CPUS];
+	/*
+	 * buffer to post messages to the host.
+	 */
+	void *post_msg_page[NR_CPUS];
 };
 
 extern struct hv_context hv_context;
-- 
1.7.4.1