x86/pv: Fix bugs with the handling of int80_bounce

Testing has revealed two issues:

 1) Passing a NULL handle to set_trap_table() is intended to flush the entire
    table.  The 64bit guest case (and 32bit guest on 32bit Xen, when it
    existed) called init_int80_direct_trap() to reset int80_bounce, but c/s
    cda335c279 which introduced the 32bit guest on 64bit Xen support omitted
    this step.  Previously therefore, it was impossible for a 32bit guest to
    reset its registered int80_bounce details.

 2) init_int80_direct_trap() doesn't honour the guests request to have
    interrupts disabled on entry.  PVops Linux requests that interrupts are
    disabled, but Xen currently leaves them enabled when following the int80
    fastpath.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 55ab172a1f
master date: 2017-05-09 19:00:04 +0100

xen/arch/x86/x86_64/compat/traps.c

@@ -324,6 +324,7 @@ int compat_set_trap_table(XEN_GUEST_HANDLE(trap_info_compat_t) traps)
     if ( guest_handle_is_null(traps) )
     {
         memset(dst, 0, NR_VECTORS * sizeof(*dst));
+        init_int80_direct_trap(current);
         return 0;
     }
 

xen/arch/x86/x86_64/traps.c

@@ -420,12 +420,13 @@ void init_int80_direct_trap(struct vcpu *v)
     struct trap_info *ti = &v->arch.pv_vcpu.trap_ctxt[0x80];
     struct trap_bounce *tb = &v->arch.pv_vcpu.int80_bounce;
 
-    tb->flags = TBF_EXCEPTION;
     tb->cs    = ti->cs;
     tb->eip   = ti->address;
 
     if ( null_trap_bounce(v, tb) )
         tb->flags = 0;
+    else
+        tb->flags = TBF_EXCEPTION | (TI_GET_IF(ti) ? TBF_INTERRUPT : 0);
 }
 
 static long register_guest_callback(struct callback_register *reg)