[Xen-devel] [PATCH 09/12] xen/gntdev: safely unmap grants in case they are still in use

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: Jenny Herbert <jennifer.herbert@xxxxxxxxxx>

Use gnttab_unmap_refs_async() to wait until the mapped pages are no
longer in use before unmapping them.

This allows userspace programs to safely use Direct I/O and AIO to a
network filesystem which may retain refs to pages in queued skbs after
the filesystem I/O has completed.

Signed-off-by: Jenny Herbert <jennifer.herbert@xxxxxxxxxx>
Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
 drivers/xen/gntdev.c |   36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 32f6bfe..a740dce 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -311,9 +311,30 @@ static int map_grant_pages(struct grant_map *map)
        return err;
 }
 
+struct unmap_grant_pages_callback_data
+{
+       struct completion completion;
+       int result;
+};
+
+static void unmap_grant_callback(int result,
+                                struct gntab_unmap_queue_data *data)
+{
+       struct unmap_grant_pages_callback_data* d = data->data;
+
+       d->result = result;
+       complete(&d->completion);
+}
+
 static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
 {
        int i, err = 0;
+       struct gntab_unmap_queue_data unmap_data;
+       struct unmap_grant_pages_callback_data data;
+
+       init_completion(&data.completion);
+       unmap_data.data = &data;
+       unmap_data.done= &unmap_grant_callback;
 
        if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                int pgno = (map->notify.addr >> PAGE_SHIFT);
@@ -325,11 +346,16 @@ static int __unmap_grant_pages(struct grant_map *map, int 
offset, int pages)
                }
        }
 
-       err = gnttab_unmap_refs(map->unmap_ops + offset,
-                       use_ptemod ? map->kunmap_ops + offset : NULL, 
map->pages + offset,
-                       pages);
-       if (err)
-               return err;
+       unmap_data.unmap_ops = map->unmap_ops + offset;
+       unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
+       unmap_data.pages = map->pages + offset;
+       unmap_data.count = pages;
+
+       gnttab_unmap_refs_async(&unmap_data);
+
+       wait_for_completion(&data.completion);
+       if (data.result)
+               return data.result;
 
        for (i = 0; i < pages; i++) {
                if (map->unmap_ops[offset+i].status)
-- 
1.7.10.4


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