diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 8db771feed3d..6eb77127bb7d 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -6,6 +6,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/dax.h>
+#include <linux/io.h>
 #include "dax-private.h"
 #include "bus.h"
 
@@ -541,7 +542,8 @@ struct dax_region *alloc_dax_region(struct device *parent, int region_id,
 }
 EXPORT_SYMBOL_GPL(alloc_dax_region);
 
-static int alloc_dev_dax_range(struct dev_dax *dev_dax, resource_size_t size)
+static int __alloc_dev_dax_range(struct dev_dax *dev_dax, u64 start,
+		resource_size_t size)
 {
 	struct dax_region *dax_region = dev_dax->region;
 	struct resource *res = &dax_region->res;
@@ -550,8 +552,34 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, resource_size_t size)
 
 	device_lock_assert(dax_region->dev);
 
+	if (dev_WARN_ONCE(&dev_dax->dev, !size, "non-zero size required\n"))
+		return -EINVAL;
+
+	/* allow default @start when the resource tree is empty */
+	if (start == U64_MAX && !res->child)
+		start = res->start;
+	if (start == U64_MAX)
+		return -EINVAL;
+
+	alloc = __request_region(res, start, size, dev_name(dev), 0);
+	if (!alloc)
+		return -ENOMEM;
+
+	dev_dax->range = (struct range) {
+		.start = alloc->start,
+		.end = alloc->end,
+	};
+
+	return 0;
+}
+
+static int alloc_dev_dax_range(struct dev_dax *dev_dax, resource_size_t size)
+{
 	/* handle the seed alloc special case */
 	if (!size) {
+		struct dax_region *dax_region = dev_dax->region;
+		struct resource *res = &dax_region->res;
+
 		dev_dax->range = (struct range) {
 			.start = res->start,
 			.end = res->start - 1,
@@ -559,18 +587,29 @@ static int alloc_dev_dax_range(struct dev_dax *dev_dax, resource_size_t size)
 		return 0;
 	}
 
-	/* TODO: handle multiple allocations per region */
-	if (res->child)
-		return -ENOMEM;
+	return __alloc_dev_dax_range(dev_dax, U64_MAX, size);
+}
 
-	alloc = __request_region(res, res->start, size, dev_name(dev), 0);
+static int __adjust_dev_dax_range(struct dev_dax *dev_dax, struct resource *res,
+		resource_size_t size)
+{
+	struct dax_region *dax_region = dev_dax->region;
+	struct range *range = &dev_dax->range;
+	int rc = 0;
 
-	if (!alloc)
-		return -ENOMEM;
+	device_lock_assert(dax_region->dev);
+
+	if (size)
+		rc = adjust_resource(res, range->start, size);
+	else
+		__release_region(&dax_region->res, range->start,
+				range_len(range));
+	if (rc)
+		return rc;
 
 	dev_dax->range = (struct range) {
-		.start = alloc->start,
-		.end = alloc->end,
+		.start = range->start,
+		.end = range->start + size - 1,
 	};
 
 	return 0;
@@ -584,7 +623,131 @@ static ssize_t size_show(struct device *dev,
 
 	return sprintf(buf, "%llu\n", size);
 }
-static DEVICE_ATTR_RO(size);
+
+static bool alloc_is_aligned(struct dax_region *dax_region,
+		resource_size_t size)
+{
+	/*
+	 * The minimum mapping granularity for a device instance is a
+	 * single subsection, unless the arch says otherwise.
+	 */
+	return IS_ALIGNED(size, max_t(unsigned long, dax_region->align,
+				memremap_compat_align()));
+}
+
+static int dev_dax_shrink(struct dev_dax *dev_dax, resource_size_t size)
+{
+	struct dax_region *dax_region = dev_dax->region;
+	struct range *range = &dev_dax->range;
+	struct resource *res, *adjust = NULL;
+	struct device *dev = &dev_dax->dev;
+
+	for_each_dax_region_resource(dax_region, res)
+		if (strcmp(res->name, dev_name(dev)) == 0
+				&& res->start == range->start) {
+			adjust = res;
+			break;
+		}
+
+	if (dev_WARN_ONCE(dev, !adjust, "failed to find matching resource\n"))
+		return -ENXIO;
+	return __adjust_dev_dax_range(dev_dax, adjust, size);
+}
+
+static ssize_t dev_dax_resize(struct dax_region *dax_region,
+		struct dev_dax *dev_dax, resource_size_t size)
+{
+	resource_size_t avail = dax_region_avail_size(dax_region), to_alloc;
+	resource_size_t dev_size = range_len(&dev_dax->range);
+	struct resource *region_res = &dax_region->res;
+	struct device *dev = &dev_dax->dev;
+	const char *name = dev_name(dev);
+	struct resource *res, *first;
+
+	if (dev->driver)
+		return -EBUSY;
+	if (size == dev_size)
+		return 0;
+	if (size > dev_size && size - dev_size > avail)
+		return -ENOSPC;
+	if (size < dev_size)
+		return dev_dax_shrink(dev_dax, size);
+
+	to_alloc = size - dev_size;
+	if (dev_WARN_ONCE(dev, !alloc_is_aligned(dax_region, to_alloc),
+			"resize of %pa misaligned\n", &to_alloc))
+		return -ENXIO;
+
+	/*
+	 * Expand the device into the unused portion of the region. This
+	 * may involve adjusting the end of an existing resource, or
+	 * allocating a new resource.
+	 */
+	first = region_res->child;
+	if (!first)
+		return __alloc_dev_dax_range(dev_dax, dax_region->res.start,
+				to_alloc);
+	for (res = first; to_alloc && res; res = res->sibling) {
+		struct resource *next = res->sibling;
+		resource_size_t free;
+
+		/* space at the beginning of the region */
+		free = 0;
+		if (res == first && res->start > dax_region->res.start)
+			free = res->start - dax_region->res.start;
+		if (free >= to_alloc && dev_size == 0)
+			return __alloc_dev_dax_range(dev_dax,
+					dax_region->res.start, to_alloc);
+
+		free = 0;
+		/* space between allocations */
+		if (next && next->start > res->end + 1)
+			free = next->start - res->end + 1;
+
+		/* space at the end of the region */
+		if (free < to_alloc && !next && res->end < region_res->end)
+			free = region_res->end - res->end;
+
+		if (free >= to_alloc && strcmp(name, res->name) == 0)
+			return __adjust_dev_dax_range(dev_dax, res,
+					resource_size(res) + to_alloc);
+		else if (free >= to_alloc && dev_size == 0)
+			return __alloc_dev_dax_range(dev_dax, res->end + 1,
+					to_alloc);
+	}
+	return -ENOSPC;
+}
+
+static ssize_t size_store(struct device *dev, struct device_attribute *attr,
+		const char *buf, size_t len)
+{
+	ssize_t rc;
+	unsigned long long val;
+	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct dax_region *dax_region = dev_dax->region;
+
+	rc = kstrtoull(buf, 0, &val);
+	if (rc)
+		return rc;
+
+	if (!alloc_is_aligned(dax_region, val)) {
+		dev_dbg(dev, "%s: size: %lld misaligned\n", __func__, val);
+		return -EINVAL;
+	}
+
+	device_lock(dax_region->dev);
+	if (!dax_region->dev->driver) {
+		device_unlock(dax_region->dev);
+		return -ENXIO;
+	}
+	device_lock(dev);
+	rc = dev_dax_resize(dax_region, dev_dax, val);
+	device_unlock(dev);
+	device_unlock(dax_region->dev);
+
+	return rc == 0 ? len : rc;
+}
+static DEVICE_ATTR_RW(size);
 
 static int dev_dax_target_node(struct dev_dax *dev_dax)
 {
@@ -633,11 +796,14 @@ static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
 {
 	struct device *dev = container_of(kobj, struct device, kobj);
 	struct dev_dax *dev_dax = to_dev_dax(dev);
+	struct dax_region *dax_region = dev_dax->region;
 
 	if (a == &dev_attr_target_node.attr && dev_dax_target_node(dev_dax) < 0)
 		return 0;
 	if (a == &dev_attr_numa_node.attr && !IS_ENABLED(CONFIG_NUMA))
 		return 0;
+	if (a == &dev_attr_size.attr && is_static(dax_region))
+		return 0444;
 	return a->mode;
 }
 
