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>

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;
 

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);
-			 * 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;
 		}
-		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;
 	}

include/xen/grant_table.h

@@ -185,6 +185,6 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 		    struct gnttab_map_grant_ref *kmap_ops,
 		    struct page **pages, unsigned int count);
 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);
 
 #endif /* __ASM_GNTTAB_H__ */