Index: xen-4.18.0-testing/xen/arch/x86/hvm/stdvga.c
===================================================================
--- xen-4.18.0-testing.orig/xen/arch/x86/hvm/stdvga.c
+++ xen-4.18.0-testing/xen/arch/x86/hvm/stdvga.c
@@ -165,7 +165,10 @@ static int stdvga_outb(uint64_t addr, ui
 
     /* When in standard vga mode, emulate here all writes to the vram buffer
      * so we can immediately satisfy reads without waiting for qemu. */
-    s->stdvga = (s->sr[7] == 0x00);
+    s->stdvga =
+        (s->sr[7] == 0x00) &&  /* standard vga mode */
+        (s->gr[6] == 0x05);    /* misc graphics register w/ MemoryMapSelect=1
+                                * 0xa0000-0xaffff (64k region), AlphaDis=1 */
 
     if ( !prev_stdvga && s->stdvga )
     {