drivers:hv: Lock access to hyperv_mmio resource tree

BugLink: http://bugs.launchpad.net/bugs/1616677

In existing code, this tree of resources is created
in single-threaded code and never modified after it is
created, and thus needs no locking.  This patch introduces
a semaphore for tree access, as other patches in this
series introduce run-time modifications of this resource
tree which can happen on multiple threads.
Signed-off-by: Jake Oshins <jakeo@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(back ported from commit e16dad6b)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

 Conflicts:
	drivers/hv/vmbus_drv.c
Acked-by: Brad Figg <brad.figg@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>

drivers/hv/vmbus_drv.c

@@ -1164,10 +1164,11 @@ int vmbus_allocate_mmio(struct resource **new, struct hv_device *device_obj,
 			resource_size_t size, resource_size_t align,
 			bool fb_overlap_ok)
 {
-	struct resource *iter, *shadow;
-	resource_size_t range_min, range_max, start;
+	struct resource *iter;
+	resource_size_t range_min, range_max, start, local_min, local_max;
 	const char *dev_n = dev_name(&device_obj->device);
-	int retval;
+	u32 fb_end = screen_info.lfb_base + (screen_info.lfb_size << 1);
+	int i, retval;
 
 	retval = -ENXIO;
 	down(&hyperv_mmio_lock);
@@ -1198,21 +1199,40 @@ int vmbus_allocate_mmio(struct resource **new, struct hv_device *device_obj,
 
 		range_min = iter->start;
 		range_max = iter->end;
-		start = (range_min + align - 1) & ~(align - 1);
-		for (; start + size - 1 <= range_max; start += align) {
-			shadow = __request_region(iter, start, size, NULL,
-						  IORESOURCE_BUSY);
-			if (!shadow)
+
+		/* If this range overlaps the frame buffer, split it into
+		   two tries. */
+		for (i = 0; i < 2; i++) {
+			local_min = range_min;
+			local_max = range_max;
+			if (fb_overlap_ok || (range_min >= fb_end) ||
+			    (range_max <= screen_info.lfb_base)) {
+				i++;
+			} else {
+				if ((range_min <= screen_info.lfb_base) &&
+				    (range_max >= screen_info.lfb_base)) {
+					/*
+					 * The frame buffer is in this window,
+					 * so trim this into the part that
+					 * preceeds the frame buffer.
+					 */
+					local_max = screen_info.lfb_base - 1;
+					range_min = fb_end;
+				} else {
+					range_min = fb_end;
 					continue;
+				}
+			}
 
-			*new = request_mem_region_exclusive(start, size, dev_n);
+			start = (local_min + align - 1) & ~(align - 1);
+			for (; start + size - 1 <= local_max; start += align) {
+				*new = request_mem_region_exclusive(start, size,
+								    dev_n);
 				if (*new) {
-				shadow->name = (char *)*new;
 					retval = 0;
 					goto exit;
 				}
-
-			__release_region(iter, start, size);
+			}
 		}
 	}