x86 shadow: Relax assertion in VRAM tracking code

The original assertion is too strict, as it includes the A/D bits of
the PTE, which (by design) can change under our feet.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>

xen/arch/x86/mm/shadow/multi.c

@@ -1117,7 +1117,8 @@ static inline void shadow_vram_put_l1e(shadow_l1e_t old_sl1e,
             }
             else
             {
-                ASSERT(dirty_vram->sl1ma[i] == sl1ma);
+                ASSERT((dirty_vram->sl1ma[i] & PAGE_MASK) 
+                       == (sl1ma & PAGE_MASK));
                 dirty_vram->sl1ma[i] = INVALID_PADDR;
                 if ( flags & _PAGE_DIRTY )
                     dirty = 1;