xen/granttable: Support transitive grants

These allow a domain A which has been granted access on a page of domain B's
memory to issue domain C with a copy-grant on the same page.  This is useful
e.g. for forwarding packets between domains.
Signed-off-by: Annie Li <annie.li@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

drivers/xen/grant-table.c

@@ -131,6 +131,18 @@ struct gnttab_ops {
 	void (*update_subpage_entry)(grant_ref_t ref, domid_t domid,
 				     unsigned long frame, int flags,
 				     unsigned page_off, unsigned length);
+	/*
+	 * Redirect an available grant entry on domain A to another grant
+	 * reference of domain B, then allow domain C to use grant reference
+	 * of domain B transitively. Ref parameter is an available grant entry
+	 * reference on domain A, domid is id of domain C which accesses grant
+	 * entry transitively, flags is grant type and flag information,
+	 * trans_domid is id of domain B whose grant entry is finally accessed
+	 * transitively, trans_gref is grant entry transitive reference of
+	 * domain B.
+	 */
+	void (*update_trans_entry)(grant_ref_t ref, domid_t domid, int flags,
+				   domid_t trans_domid, grant_ref_t trans_gref);
 };
 
 static struct gnttab_ops *gnttab_interface;
@@ -332,6 +344,63 @@ bool gnttab_subpage_grants_available(void)
 }
 EXPORT_SYMBOL_GPL(gnttab_subpage_grants_available);
 
+void gnttab_update_trans_entry_v2(grant_ref_t ref, domid_t domid,
+				  int flags, domid_t trans_domid,
+				  grant_ref_t trans_gref)
+{
+	gnttab_shared.v2[ref].transitive.trans_domid = trans_domid;
+	gnttab_shared.v2[ref].transitive.gref = trans_gref;
+	gnttab_shared.v2[ref].hdr.domid = domid;
+	wmb();
+	gnttab_shared.v2[ref].hdr.flags =
+				GTF_permit_access | GTF_transitive | flags;
+}
+
+int gnttab_grant_foreign_access_trans_ref(grant_ref_t ref, domid_t domid,
+					  int flags, domid_t trans_domid,
+					  grant_ref_t trans_gref)
+{
+	if (flags & (GTF_accept_transfer | GTF_reading |
+		     GTF_writing | GTF_sub_page))
+		return -EPERM;
+
+	if (gnttab_interface->update_trans_entry == NULL)
+		return -ENOSYS;
+
+	gnttab_interface->update_trans_entry(ref, domid, flags, trans_domid,
+					     trans_gref);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_trans_ref);
+
+int gnttab_grant_foreign_access_trans(domid_t domid, int flags,
+				      domid_t trans_domid,
+				      grant_ref_t trans_gref)
+{
+	int ref, rc;
+
+	ref = get_free_entries(1);
+	if (unlikely(ref < 0))
+		return -ENOSPC;
+
+	rc = gnttab_grant_foreign_access_trans_ref(ref, domid, flags,
+						   trans_domid, trans_gref);
+	if (rc < 0) {
+		put_free_entry(ref);
+		return rc;
+	}
+
+	return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_trans);
+
+bool gnttab_trans_grants_available(void)
+{
+	return gnttab_interface->update_trans_entry != NULL;
+}
+EXPORT_SYMBOL_GPL(gnttab_trans_grants_available);
+
 static int gnttab_query_foreign_access_v1(grant_ref_t ref)
 {
 	return gnttab_shared.v1[ref].flags & (GTF_reading|GTF_writing);
@@ -885,6 +954,7 @@ static struct gnttab_ops gnttab_v2_ops = {
 	.end_foreign_transfer_ref	= gnttab_end_foreign_transfer_ref_v2,
 	.query_foreign_access		= gnttab_query_foreign_access_v2,
 	.update_subpage_entry		= gnttab_update_subpage_entry_v2,
+	.update_trans_entry		= gnttab_update_trans_entry_v2,
 };
 
 static void gnttab_request_version(void)

include/xen/grant_table.h

@@ -65,6 +65,9 @@ int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
 int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
 					int flags, unsigned page_off,
 					unsigned length);
+int gnttab_grant_foreign_access_trans(domid_t domid, int flags,
+				      domid_t trans_domid,
+				      grant_ref_t trans_gref);
 
 /*
  * Are sub-page grants available on this version of Xen?  Returns true if they
@@ -72,6 +75,12 @@ int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
  */
 bool gnttab_subpage_grants_available(void);
 
+/*
+ * Are transitive grants available on this version of Xen?  Returns true if they
+ * are, and false if they're not.
+ */
+bool gnttab_trans_grants_available(void);
+
 /*
  * End access through the given grant reference, iff the grant entry is no
  * longer in use.  Return 1 if the grant entry was freed, 0 if it is still in
@@ -121,6 +130,9 @@ int gnttab_grant_foreign_access_subpage_ref(grant_ref_t ref, domid_t domid,
 					    unsigned long frame, int flags,
 					    unsigned page_off,
 					    unsigned length);
+int gnttab_grant_foreign_access_trans_ref(grant_ref_t ref, domid_t domid,
+					  int flags, domid_t trans_domid,
+					  grant_ref_t trans_gref);
 
 void gnttab_grant_foreign_transfer_ref(grant_ref_t, domid_t domid,
 				       unsigned long pfn);