--- zzzz-none-000/linux-3.10.107/drivers/hv/ring_buffer.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/drivers/hv/ring_buffer.c	2021-02-04 17:41:59.000000000 +0000
@@ -26,6 +26,7 @@
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/hyperv.h>
+#include <linux/uio.h>
 
 #include "hyperv_vmbus.h"
 
@@ -75,6 +76,8 @@
 	if (rbi->ring_buffer->interrupt_mask)
 		return false;
 
+	/* check interrupt_mask before read_index */
+	rmb();
 	/*
 	 * This is the only case we need to signal when the
 	 * ring transitions from being empty to non-empty.
@@ -100,10 +103,9 @@
  *    there is room for the producer to send the pending packet.
  */
 
-static bool hv_need_to_signal_on_read(u32 old_rd,
-					 struct hv_ring_buffer_info *rbi)
+static bool hv_need_to_signal_on_read(u32 prev_write_sz,
+				      struct hv_ring_buffer_info *rbi)
 {
-	u32 prev_write_sz;
 	u32 cur_write_sz;
 	u32 r_size;
 	u32 write_loc = rbi->ring_buffer->write_index;
@@ -120,10 +122,6 @@
 	cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
 			read_loc - write_loc;
 
-	prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
-			old_rd - write_loc;
-
-
 	if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
 		return true;
 
@@ -358,6 +356,11 @@
 	ring_info->ring_buffer->read_index =
 		ring_info->ring_buffer->write_index = 0;
 
+	/*
+	 * Set the feature bit for enabling flow control.
+	 */
+	ring_info->ring_buffer->feature_bits.value = 1;
+
 	ring_info->ring_size = buflen;
 	ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
 
@@ -385,23 +388,20 @@
  *
  */
 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
-		    struct scatterlist *sglist, u32 sgcount, bool *signal)
+		    struct kvec *kv_list, u32 kv_count, bool *signal)
 {
 	int i = 0;
 	u32 bytes_avail_towrite;
 	u32 bytes_avail_toread;
 	u32 totalbytes_towrite = 0;
 
-	struct scatterlist *sg;
 	u32 next_write_location;
 	u32 old_write;
 	u64 prev_indices = 0;
 	unsigned long flags;
 
-	for_each_sg(sglist, sg, sgcount, i)
-	{
-		totalbytes_towrite += sg->length;
-	}
+	for (i = 0; i < kv_count; i++)
+		totalbytes_towrite += kv_list[i].iov_len;
 
 	totalbytes_towrite += sizeof(u64);
 
@@ -425,12 +425,11 @@
 
 	old_write = next_write_location;
 
-	for_each_sg(sglist, sg, sgcount, i)
-	{
+	for (i = 0; i < kv_count; i++) {
 		next_write_location = hv_copyto_ringbuffer(outring_info,
 						     next_write_location,
-						     sg_virt(sg),
-						     sg->length);
+						     kv_list[i].iov_base,
+						     kv_list[i].iov_len);
 	}
 
 	/* Set previous packet start */
@@ -513,7 +512,6 @@
 	u32 next_read_location = 0;
 	u64 prev_indices = 0;
 	unsigned long flags;
-	u32 old_read;
 
 	if (buflen <= 0)
 		return -EINVAL;
@@ -524,8 +522,6 @@
 				&bytes_avail_toread,
 				&bytes_avail_towrite);
 
-	old_read = bytes_avail_toread;
-
 	/* Make sure there is something to read */
 	if (bytes_avail_toread < buflen) {
 		spin_unlock_irqrestore(&inring_info->ring_lock, flags);
@@ -556,7 +552,7 @@
 
 	spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 
-	*signal = hv_need_to_signal_on_read(old_read, inring_info);
+	*signal = hv_need_to_signal_on_read(bytes_avail_towrite, inring_info);
 
 	return 0;
 }