xen/grant-table: Support mappings required by blkback

Add support for mappings without GNTMAP_contains_pte. This was not
supported because the unmap operation assumed that this flag was being
used; adding a parameter to the unmap operation to allow the PTE
clearing to be disabled is sufficient to make unmap capable of
supporting either mapping type.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
[v1: Fix cleanpatch warnings]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

2 files changed, 7 insertions, 20 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index f52f661f8f82..99d8151c824a 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -314,7 +314,8 @@ static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
                 }
         }
 
-        err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, pages);
+        err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset,
+                                pages, true);
         if (err)
                 return err;
 
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index a3d0e1e278c1..1cd94daa71db 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -761,24 +761,10 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
                                 (map_ops[i].host_addr & ~PAGE_MASK));
                         mfn = pte_mfn(*pte);
                 } else {
-                        /* If you really wanted to do this:
-                         * mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
-                         *
-                         * The reason we do not implement it is b/c on the
-                         * unmap path (gnttab_unmap_refs) we have no means of
-                         * checking whether the page is !GNTMAP_contains_pte.
-                         *
-                         * That is without some extra data-structure to carry
-                         * the struct page, bool clear_pte, and list_head next
-                         * tuples and deal with allocation/delallocation, etc.
-                         *
-                         * The users of this API set the GNTMAP_contains_pte
-                         * flag so lets just return not supported until it
-                         * becomes neccessary to implement.
-                         */
-                        return -EOPNOTSUPP;
+                        mfn = PFN_DOWN(map_ops[i].dev_bus_addr);
                 }
-                ret = m2p_add_override(mfn, pages[i], &kmap_ops[i]);
+                ret = m2p_add_override(mfn, pages[i], kmap_ops ?
+                                       &kmap_ops[i] : NULL);
                 if (ret)
                         return ret;
         }
@@ -788,7 +774,7 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 EXPORT_SYMBOL_GPL(gnttab_map_refs);
 
 int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
-                      struct page **pages, unsigned int count)
+                      struct page **pages, unsigned int count, bool clear_pte)
 {
         int i, ret;
 
@@ -800,7 +786,7 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
                 return ret;
 
         for (i = 0; i < count; i++) {
-                ret = m2p_remove_override(pages[i], true /* clear the PTE */);
+                ret = m2p_remove_override(pages[i], clear_pte);
                 if (ret)
                         return ret;
         }