Drivers: hv: ring_buffer: wrap around mappings for ring buffers

Make it possible to always use a single memcpy() or to provide a direct
link to a packet on the ring buffer by creating virtual mapping for two
copies of the ring buffer with vmap(). Utilize currently empty
hv_ringbuffer_cleanup() to do the unmap.

While on it, replace sizeof(struct hv_ring_buffer) check
in hv_ringbuffer_init() with BUILD_BUG_ON() as it is a compile time check.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 33 insertions, 6 deletions

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index e3edcaee7ab3..7e21c2c82ad1 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -27,6 +27,8 @@
 #include <linux/mm.h>
 #include <linux/hyperv.h>
 #include <linux/uio.h>
+#include <linux/vmalloc.h>
+#include <linux/slab.h>
 
 #include "hyperv_vmbus.h"
 
@@ -243,22 +245,46 @@ void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 
 /* Initialize the ring buffer. */
 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
-		   void *buffer, u32 buflen)
+		       struct page *pages, u32 page_cnt)
 {
-	if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
-		return -EINVAL;
+	int i;
+	struct page **pages_wraparound;
+
+	BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE));
 
 	memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
 
-	ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
+	/*
+	 * First page holds struct hv_ring_buffer, do wraparound mapping for
+	 * the rest.
+	 */
+	pages_wraparound = kzalloc(sizeof(struct page *) * (page_cnt * 2 - 1),
+				   GFP_KERNEL);
+	if (!pages_wraparound)
+		return -ENOMEM;
+
+	pages_wraparound[0] = pages;
+	for (i = 0; i < 2 * (page_cnt - 1); i++)
+		pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1];
+
+	ring_info->ring_buffer = (struct hv_ring_buffer *)
+		vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL);
+
+	kfree(pages_wraparound);
+
+
+	if (!ring_info->ring_buffer)
+		return -ENOMEM;
+
 	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);
+	ring_info->ring_size = page_cnt << PAGE_SHIFT;
+	ring_info->ring_datasize = ring_info->ring_size -
+		sizeof(struct hv_ring_buffer);
 
 	spin_lock_init(&ring_info->ring_lock);
 
@@ -268,6 +294,7 @@ int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 /* Cleanup the ring buffer. */
 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 {
+	vunmap(ring_info->ring_buffer);
 }
 
 /* Write to the ring buffer. */