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>

2 files changed, 82 insertions, 0 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index c8312c7056f1..a3d0e1e278c1 100644
--- a/drivers/xen/grant-table.c
+++ b/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)
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index 2b492b9637b3..f1e17b70588b 100644
--- a/include/xen/grant_table.h
+++ b/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
@@ -73,6 +76,12 @@ 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
  * use.
@@ -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);