x86: fix initialization of 'l' bit in ldt descriptors

Make sure that fill_ldt() initializes the 'l' bit in the descriptor.
It always sets it to 0, ignoring 'lm' in user_desc, preserving original
x86_64 behaviour.

Previously it was leaving 'l' uninitialized.
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Cc: Glauber de Oliveira Costa <gcosta@redhat.com>

include/asm-x86/desc.h

@@ -24,6 +24,11 @@ static inline void fill_ldt(struct desc_struct *desc,
 	desc->d = info->seg_32bit;
 	desc->g = info->limit_in_pages;
 	desc->base2 = (info->base_addr & 0xff000000) >> 24;
+	/*
+	 * Don't allow setting of the lm bit. It is useless anyway
+	 * because 64bit system calls require __USER_CS:
+	 */
+	desc->l = 0;
 }
 
 extern struct desc_ptr idt_descr;