xen/grant-table: Add an helper to iterate over a specific number of grants

With the 64KB page granularity support on ARM64, a Linux page may be
split accross multiple grant.

Currently we have the helper gnttab_foreach_grant_in_grant to break a
Linux page based on an offset and a len, but it doesn't fit when we only
have a number of grants in hand.

Introduce a new helper which take an array of Linux page and a number of
grant and will figure out the address of each grant.

Signed-off-by: Julien Grall <julien.grall@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

2 files changed, 28 insertions, 0 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 72d633962095..c49f79ed58c5 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -802,6 +802,28 @@ void gnttab_foreach_grant_in_range(struct page *page,
 }
 EXPORT_SYMBOL_GPL(gnttab_foreach_grant_in_range);
 
+void gnttab_foreach_grant(struct page **pages,
+                          unsigned int nr_grefs,
+                          xen_grant_fn_t fn,
+                          void *data)
+{
+        unsigned int goffset = 0;
+        unsigned long xen_pfn = 0;
+        unsigned int i;
+
+        for (i = 0; i < nr_grefs; i++) {
+                if ((i % XEN_PFN_PER_PAGE) == 0) {
+                        xen_pfn = page_to_xen_pfn(pages[i / XEN_PFN_PER_PAGE]);
+                        goffset = 0;
+                }
+
+                fn(pfn_to_gfn(xen_pfn), goffset, XEN_PAGE_SIZE, data);
+
+                goffset += XEN_PAGE_SIZE;
+                xen_pfn++;
+        }
+}
+
 int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
                     struct gnttab_map_grant_ref *kmap_ops,
                     struct page **pages, unsigned int count)
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index e17a4b381a16..34b1379f9777 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -264,6 +264,12 @@ static inline void gnttab_for_one_grant(struct page *page, unsigned int offset,
         gnttab_foreach_grant_in_range(page, offset, len, fn, data);
 }
 
+/* Get @nr_grefs grants from an array of page and call fn for each grant */
+void gnttab_foreach_grant(struct page **pages,
+                          unsigned int nr_grefs,
+                          xen_grant_fn_t fn,
+                          void *data);
+
 /* Get the number of grant in a specified region
  *
  * start: Offset from the beginning of the first page