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>

drivers/hv/channel.c

@@ -75,7 +75,6 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 {
 	struct vmbus_channel_open_channel *open_msg;
 	struct vmbus_channel_msginfo *open_info = NULL;
-	void *in, *out;
 	unsigned long flags;
 	int ret, err = 0;
 	struct page *page;
@@ -112,23 +111,21 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 		goto error_set_chnstate;
 	}
 
-	out = page_address(page);
-	in = (void *)((unsigned long)out + send_ringbuffer_size);
-
-	newchannel->ringbuffer_pages = out;
+	newchannel->ringbuffer_pages = page_address(page);
 	newchannel->ringbuffer_pagecount = (send_ringbuffer_size +
 					   recv_ringbuffer_size) >> PAGE_SHIFT;
 
-	ret = hv_ringbuffer_init(
-		&newchannel->outbound, out, send_ringbuffer_size);
+	ret = hv_ringbuffer_init(&newchannel->outbound, page,
+				 send_ringbuffer_size >> PAGE_SHIFT);
 
 	if (ret != 0) {
 		err = ret;
 		goto error_free_pages;
 	}
 
-	ret = hv_ringbuffer_init(
-		&newchannel->inbound, in, recv_ringbuffer_size);
+	ret = hv_ringbuffer_init(&newchannel->inbound,
+				 &page[send_ringbuffer_size >> PAGE_SHIFT],
+				 recv_ringbuffer_size >> PAGE_SHIFT);
 	if (ret != 0) {
 		err = ret;
 		goto error_free_pages;
@@ -139,7 +136,7 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 	newchannel->ringbuffer_gpadlhandle = 0;
 
 	ret = vmbus_establish_gpadl(newchannel,
-					 newchannel->outbound.ring_buffer,
+				    page_address(page),
 				    send_ringbuffer_size +
 				    recv_ringbuffer_size,
 				    &newchannel->ringbuffer_gpadlhandle);
@@ -214,7 +211,9 @@ int vmbus_open(struct vmbus_channel *newchannel, u32 send_ringbuffer_size,
 	vmbus_teardown_gpadl(newchannel, newchannel->ringbuffer_gpadlhandle);
 	kfree(open_info);
 error_free_pages:
-	free_pages((unsigned long)out,
+	hv_ringbuffer_cleanup(&newchannel->outbound);
+	hv_ringbuffer_cleanup(&newchannel->inbound);
+	__free_pages(page,
 		     get_order(send_ringbuffer_size + recv_ringbuffer_size));
 error_set_chnstate:
 	newchannel->state = CHANNEL_OPEN_STATE;

drivers/hv/hyperv_vmbus.h

@@ -522,8 +522,8 @@ extern unsigned int host_info_edx;
 /* Interface */
 
 
-int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info, void *buffer,
-		   u32 buflen);
+int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
+		       struct page *pages, u32 pagecnt);
 
 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info);
 

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. */