[Xen-devel] [PATCH V2 2/2] xen/granttable: Support transitive grants

[annie.li@xxxxxxxxxx]

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@xxxxxxxxxx>
---
 drivers/xen/grant-table.c |   73 +++++++++++++++++++++++++++++++++++++++++++++
 include/xen/grant_table.h |   12 +++++++
 2 files changed, 85 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 4a10e3f..db3e7c0 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -130,6 +130,18 @@ struct gnttab_ops {
         */
        void (*update_subpage_entry)(grant_ref_t, domid_t, unsigned long, int,
                                     unsigned, unsigned);
+       /*
+        * 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. First parameter is an available grant entry
+        * reference on domain A, second one is id of domain C which accesses
+        * grant entry transitively, third one is grant type and flag
+        * information, forth one is id of domain B whose grant entry is finally
+        * accessed transitively, last one is grant entry transitive reference
+        * of domain B.
+        */
+       void (*update_trans_entry)(grant_ref_t, domid_t, int, domid_t,
+                                  grant_ref_t);
 };
 
 static struct gnttab_ops *gnttab_interface;
@@ -334,6 +346,66 @@ 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;
+
+       if (flags & (GTF_accept_transfer | GTF_reading |
+                    GTF_writing | GTF_sub_page))
+               return -EPERM;
+
+       if (gnttab_interface->update_trans_entry == NULL)
+               return -ENOSYS;
+
+       ref = get_free_entries(1);
+       if (unlikely(ref < 0))
+               return -ENOSPC;
+
+       gnttab_interface->update_trans_entry(ref, domid, flags, trans_domid,
+                                            trans_gref);
+
+       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);
@@ -887,6 +959,7 @@ 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 2b492b9..f1e17b7 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);
-- 
1.7.6.4


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