x86/mm: fix detection of last L1 entry in modify_xen_mappings_lite()

The current logic to detect when to switch to the next L1 table is incorrectly
using l2_table_offset() in order to notice when the last entry on the current
L1 table has been reached.

It should instead use l1_table_offset() to check whether the index has wrapped
to point to the first entry, and so the next L1 table should be used.

Fixes: 8676092a0f ('x86/livepatch: Fix livepatch application when CET is active')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7c81558208
master date: 2024-03-11 11:09:42 +0000

xen/arch/x86/mm.c

@@ -5963,7 +5963,7 @@ void init_or_livepatch modify_xen_mappings_lite(
 
                 v += 1UL << L1_PAGETABLE_SHIFT;
 
-                if ( l2_table_offset(v) == 0 )
+                if ( l1_table_offset(v) == 0 )
                     break;
             }