2 files changed, 85 insertions, 0 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 1589ea1a2445..c8312c7056f1 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -120,6 +120,17 @@ struct gnttab_ops {
          * by bit operations.
          */
         int (*query_foreign_access)(grant_ref_t ref);
+        /*
+         * Grant a domain to access a range of bytes within the page referred by
+         * an available grant entry. Ref parameter is reference of a grant entry
+         * which will be sub-page accessed, domid is id of grantee domain, frame
+         * is frame address of subpage grant, flags is grant type and flag
+         * information, page_off is offset of the range of bytes, and length is
+         * length of bytes to be accessed.
+         */
+        void (*update_subpage_entry)(grant_ref_t ref, domid_t domid,
+                                     unsigned long frame, int flags,
+                                     unsigned page_off, unsigned length);
 };
 
 static struct gnttab_ops *gnttab_interface;
@@ -261,6 +272,66 @@ int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
 }
 EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access);
 
+void gnttab_update_subpage_entry_v2(grant_ref_t ref, domid_t domid,
+                                    unsigned long frame, int flags,
+                                    unsigned page_off,
+                                    unsigned length)
+{
+        gnttab_shared.v2[ref].sub_page.frame = frame;
+        gnttab_shared.v2[ref].sub_page.page_off = page_off;
+        gnttab_shared.v2[ref].sub_page.length = length;
+        gnttab_shared.v2[ref].hdr.domid = domid;
+        wmb();
+        gnttab_shared.v2[ref].hdr.flags =
+                                GTF_permit_access | GTF_sub_page | flags;
+}
+
+int gnttab_grant_foreign_access_subpage_ref(grant_ref_t ref, domid_t domid,
+                                            unsigned long frame, int flags,
+                                            unsigned page_off,
+                                            unsigned length)
+{
+        if (flags & (GTF_accept_transfer | GTF_reading |
+                     GTF_writing | GTF_transitive))
+                return -EPERM;
+
+        if (gnttab_interface->update_subpage_entry == NULL)
+                return -ENOSYS;
+
+        gnttab_interface->update_subpage_entry(ref, domid, frame, flags,
+                                               page_off, length);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage_ref);
+
+int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
+                                        int flags, unsigned page_off,
+                                        unsigned length)
+{
+        int ref, rc;
+
+        ref = get_free_entries(1);
+        if (unlikely(ref < 0))
+                return -ENOSPC;
+
+        rc = gnttab_grant_foreign_access_subpage_ref(ref, domid, frame, flags,
+                                                     page_off, length);
+        if (rc < 0) {
+                put_free_entry(ref);
+                return rc;
+        }
+
+        return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_subpage);
+
+bool gnttab_subpage_grants_available(void)
+{
+        return gnttab_interface->update_subpage_entry != NULL;
+}
+EXPORT_SYMBOL_GPL(gnttab_subpage_grants_available);
+
 static int gnttab_query_foreign_access_v1(grant_ref_t ref)
 {
         return gnttab_shared.v1[ref].flags & (GTF_reading|GTF_writing);
@@ -813,6 +884,7 @@ static struct gnttab_ops gnttab_v2_ops = {
         .end_foreign_access_ref         = gnttab_end_foreign_access_ref_v2,
         .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,
 };
 
 static void gnttab_request_version(void)
diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h
index fea4954174f0..2b492b9637b3 100644
--- a/include/xen/grant_table.h
+++ b/include/xen/grant_table.h
@@ -62,6 +62,15 @@ int gnttab_resume(void);
 
 int gnttab_grant_foreign_access(domid_t domid, unsigned long frame,
                                 int readonly);
+int gnttab_grant_foreign_access_subpage(domid_t domid, unsigned long frame,
+                                        int flags, unsigned page_off,
+                                        unsigned length);
+
+/*
+ * Are sub-page grants available on this version of Xen?  Returns true if they
+ * are, and false if they're not.
+ */
+bool gnttab_subpage_grants_available(void);
 
 /*
  * End access through the given grant reference, iff the grant entry is no
@@ -108,6 +117,10 @@ void gnttab_cancel_free_callback(struct gnttab_free_callback *callback);
 
 void gnttab_grant_foreign_access_ref(grant_ref_t ref, domid_t domid,
                                      unsigned long frame, int readonly);
+int gnttab_grant_foreign_access_subpage_ref(grant_ref_t ref, domid_t domid,
+                                            unsigned long frame, int flags,
+                                            unsigned page_off,
+                                            unsigned length);
 
 void gnttab_grant_foreign_transfer_ref(grant_ref_t, domid_t domid,
                                        unsigned long pfn);