diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -74,11 +74,10 @@
     printk("HVM: %s enabled\n", fns->name);
 
     /*
-     * Allow direct access to the PC debug ports 0x80 and 0xed (they are
-     * often used for I/O delays, but the vmexits simply slow things down).
+     * Allow direct access to the PC debug ports 0xed (it is often used
+     * for I/O delays, but the vmexits simply slow things down).
      */
     memset(hvm_io_bitmap, ~0, sizeof(hvm_io_bitmap));
-    __clear_bit(0x80, hvm_io_bitmap);
     __clear_bit(0xed, hvm_io_bitmap);
 
     hvm_funcs   = *fns;
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -1451,6 +1451,12 @@
     setup_vmcs_dump();
 
     hvm_enable(&vmx_function_table);
+
+    /*
+     * Allow direct access to the PC debug ports 0x80, which is used for I/O
+     * delays.  On some AMD chipsets it is problematic, but not on Intel.
+     */
+    __clear_bit(0x80, hvm_io_bitmap);
 }
 
 /*