[Xen-devel] [PATCH] xen-gntdev: Fix unmap notify on PV domains

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

In paravirtualized guests, the struct page* for mappings is only a
placeholder, and cannot be used to access the granted memory. Use the
userspace mapping that we have set up in order to implement
UNMAP_NOTIFY_CLEAR_BYTE.
    
Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 06de2c0..2b67f15 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -287,7 +287,12 @@ static int unmap_grant_pages(struct grant_map *map, int 
offset, int pages)
 
        if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
                int pgno = (map->notify.addr >> PAGE_SHIFT);
-               if (pgno >= offset && pgno < offset + pages) {
+               if (pgno >= offset && pgno < offset + pages && use_ptemod) {
+                       void __user *tmp;
+                       tmp = map->vma->vm_start + map->notify.addr;
+                       copy_to_user(tmp, &err, 1);
+                       map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
+               } else if (pgno >= offset && pgno < offset + pages) {
                        uint8_t *tmp = kmap(map->pages[pgno]);
                        tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
                        kunmap(map->pages[pgno]);
@@ -296,7 +301,7 @@ static int unmap_grant_pages(struct grant_map *map, int 
offset, int pages)
        }
 
        pr_debug("map %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
-       err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages, pages);
+       err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, 
pages);
        if (err)
                return err;
 

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