mm: introduce find_dev_pagemap()

There are several scenarios where we need to retrieve and update
metadata associated with a given devm_memremap_pages() mapping, and the
only lookup key available is a pfn in the range:

1/ We want to augment vmemmap_populate() (called via arch_add_memory())
   to allocate memmap storage from pre-allocated pages reserved by the
   device driver.  At vmemmap_alloc_block_buf() time it grabs device pages
   rather than page allocator pages.  This is in support of
   devm_memremap_pages() mappings where the memmap is too large to fit in
   main memory (i.e. large persistent memory devices).

2/ Taking a reference against the mapping when inserting device pages
   into the address_space radix of a given inode.  This facilitates
   unmap_mapping_range() and truncate_inode_pages() operations when the
   driver is tearing down the mapping.

3/ get_user_pages() operations on ZONE_DEVICE memory require taking a
   reference against the mapping so that the driver teardown path can
   revoke and drain usage of device pages.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 77 insertions, 8 deletions

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 449cb6a5d9a1..61cfbf4d3054 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -10,6 +10,8 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  */
+#include <linux/radix-tree.h>
+#include <linux/memremap.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/pfn_t.h>
@@ -155,22 +157,57 @@ pfn_t phys_to_pfn_t(dma_addr_t addr, unsigned long flags)
 EXPORT_SYMBOL(phys_to_pfn_t);
 
 #ifdef CONFIG_ZONE_DEVICE
+static DEFINE_MUTEX(pgmap_lock);
+static RADIX_TREE(pgmap_radix, GFP_KERNEL);
+#define SECTION_MASK ~((1UL << PA_SECTION_SHIFT) - 1)
+#define SECTION_SIZE (1UL << PA_SECTION_SHIFT)
+
 struct page_map {
         struct resource res;
+        struct percpu_ref *ref;
+        struct dev_pagemap pgmap;
 };
 
-static void devm_memremap_pages_release(struct device *dev, void *res)
+static void pgmap_radix_release(struct resource *res)
+{
+        resource_size_t key;
+
+        mutex_lock(&pgmap_lock);
+        for (key = res->start; key <= res->end; key += SECTION_SIZE)
+                radix_tree_delete(&pgmap_radix, key >> PA_SECTION_SHIFT);
+        mutex_unlock(&pgmap_lock);
+}
+
+static void devm_memremap_pages_release(struct device *dev, void *data)
 {
-        struct page_map *page_map = res;
+        struct page_map *page_map = data;
+        struct resource *res = &page_map->res;
+        resource_size_t align_start, align_size;
+
+        pgmap_radix_release(res);
 
         /* pages are dead and unused, undo the arch mapping */
-        arch_remove_memory(page_map->res.start, resource_size(&page_map->res));
+        align_start = res->start & ~(SECTION_SIZE - 1);
+        align_size = ALIGN(resource_size(res), SECTION_SIZE);
+        arch_remove_memory(align_start, align_size);
+}
+
+/* assumes rcu_read_lock() held at entry */
+struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
+{
+        struct page_map *page_map;
+
+        WARN_ON_ONCE(!rcu_read_lock_held());
+
+        page_map = radix_tree_lookup(&pgmap_radix, phys >> PA_SECTION_SHIFT);
+        return page_map ? &page_map->pgmap : NULL;
 }
 
 void *devm_memremap_pages(struct device *dev, struct resource *res)
 {
         int is_ram = region_intersects(res->start, resource_size(res),
                         "System RAM");
+        resource_size_t key, align_start, align_size;
         struct page_map *page_map;
         int error, nid;
 
@@ -190,18 +227,50 @@ void *devm_memremap_pages(struct device *dev, struct resource *res)
 
         memcpy(&page_map->res, res, sizeof(*res));
 
+        page_map->pgmap.dev = dev;
+        mutex_lock(&pgmap_lock);
+        error = 0;
+        for (key = res->start; key <= res->end; key += SECTION_SIZE) {
+                struct dev_pagemap *dup;
+
+                rcu_read_lock();
+                dup = find_dev_pagemap(key);
+                rcu_read_unlock();
+                if (dup) {
+                        dev_err(dev, "%s: %pr collides with mapping for %s\n",
+                                        __func__, res, dev_name(dup->dev));
+                        error = -EBUSY;
+                        break;
+                }
+                error = radix_tree_insert(&pgmap_radix, key >> PA_SECTION_SHIFT,
+                                page_map);
+                if (error) {
+                        dev_err(dev, "%s: failed: %d\n", __func__, error);
+                        break;
+                }
+        }
+        mutex_unlock(&pgmap_lock);
+        if (error)
+                goto err_radix;
+
         nid = dev_to_node(dev);
         if (nid < 0)
                 nid = numa_mem_id();
 
-        error = arch_add_memory(nid, res->start, resource_size(res), true);
-        if (error) {
-                devres_free(page_map);
-                return ERR_PTR(error);
-        }
+        align_start = res->start & ~(SECTION_SIZE - 1);
+        align_size = ALIGN(resource_size(res), SECTION_SIZE);
+        error = arch_add_memory(nid, align_start, align_size, true);
+        if (error)
+                goto err_add_memory;
 
         devres_add(dev, page_map);
         return __va(res->start);
+
+ err_add_memory:
+ err_radix:
+        pgmap_radix_release(res);
+        devres_free(page_map);
+        return ERR_PTR(error);
 }
 EXPORT_SYMBOL(devm_memremap_pages);
 #endif /* CONFIG_ZONE_DEVICE */