[PATCH 3/3] gnttab: GTF_sub_page is a v2-only flag

[Jan Beulich <jbeulich@suse.com>]

Prior to its introduction, v1 entries weren't checked for this flag, and
the flag also has been meaningless for v1 entries. Therefore it also
shouldn't be checked. (The only consistent alternative would be to also
check for all currently undefined flags to be clear.)

Fixes: b545941b6638 ("Implement sub-page grant support")
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -762,13 +762,11 @@ static int _set_status_v1(const grant_en
                           struct domain *rd,
                           struct active_grant_entry *act,
                           int readonly,
-                          int mapflag,
-                          domid_t  ldomid)
+                          domid_t ldomid)
 {
     int rc = GNTST_okay;
     uint32_t *raw_shah = (uint32_t *)shah;
     union grant_combo scombo;
-    uint16_t mask = GTF_type_mask;
 
     /*
      * We bound the number of times we retry CMPXCHG on memory locations that
@@ -780,11 +778,6 @@ static int _set_status_v1(const grant_en
      */
     int retries = 0;
 
-    /* if this is a grant mapping operation we should ensure GTF_sub_page
-       is not set */
-    if ( mapflag )
-        mask |= GTF_sub_page;
-
     scombo.raw = ACCESS_ONCE(*raw_shah);
 
     /*
@@ -798,8 +791,9 @@ static int _set_status_v1(const grant_en
         union grant_combo prev, new;
 
         /* If not already pinned, check the grant domid and type. */
-        if ( !act->pin && (((scombo.flags & mask) != GTF_permit_access) ||
-                           (scombo.domid != ldomid)) )
+        if ( !act->pin &&
+             (((scombo.flags & GTF_type_mask) != GTF_permit_access) ||
+              (scombo.domid != ldomid)) )
             PIN_FAIL(done, GNTST_general_error,
                      "Bad flags (%x) or dom (%d); expected d%d\n",
                      scombo.flags, scombo.domid, ldomid);
@@ -916,7 +910,7 @@ static int _set_status(const grant_entry
 {
 
     if ( evaluate_nospec(rgt_version == 1) )
-        return _set_status_v1(shah, rd, act, readonly, mapflag, ldomid);
+        return _set_status_v1(shah, rd, act, readonly, ldomid);
     else
         return _set_status_v2(shah, status, rd, act, readonly, mapflag, ldomid);
 }
--- a/xen/include/public/grant_table.h
+++ b/xen/include/public/grant_table.h
@@ -175,7 +175,7 @@ typedef struct grant_entry_v1 grant_entr
  *                             mappings of the grant [GST]
  *  GTF_sub_page: Grant access to only a subrange of the page.  @domid
  *                will only be allowed to copy from the grant, and not
- *                map it. [GST]
+ *                map it. [GST, v2]
  */
 #define _GTF_readonly       (2)
 #define GTF_readonly        (1U<<_GTF_readonly)