SMP - Force TLB flush before scheduling a process

- this makes sure that each process always run with updated TLB

- this is the simplest way how to achieve the consistency. As it means
  significant performace degradation when not require, this is nto the
  final solution and will be refined

kernel/arch/i386/include/arch_proto.h

@@ -109,6 +109,8 @@ _PROTOTYPE(void __switch_address_space, (struct proc * p,
 #define switch_address_space(proc)	\
 	__switch_address_space(proc, get_cpulocal_var_ptr(ptproc))
 
+_PROTOTYPE(void refresh_tlb, (void));
+
 /* protect.c */
 struct tss_s {
   reg_t backlink;

kernel/arch/i386/klib.S

@@ -803,9 +803,11 @@ ENTRY(__switch_address_space)
 	 * test if the cr3 is loaded with the current value to avoid unnecessary
 	 * TLB flushes
 	 */
+#if 0
 	mov	%cr3, %ecx
 	cmp	%ecx, %eax
 	je	0f
+#endif
 	mov	%eax, %cr3
 	/* get ptproc */
 	mov	8(%esp), %eax
@@ -872,10 +874,12 @@ ENTRY(eoi_8259_slave)
 	outb	$INT2_CTL
 	ret
 	
-.data
-idt_ptr:
-	.short 0x3ff
-	.long 0x0
+/* in some cases we need to force TLB update, reloading cr3 does the trick */
+ENTRY(refresh_tlb)
+	mov	%cr3, %eax
+	mov	%eax, %cr3
+	ret
+
 #ifdef CONFIG_SMP
 
 /*===========================================================================*/
@@ -1043,3 +1047,8 @@ ENTRY(switch_k_stack)
 
 	/* NOT_REACHABLE */
 0:	jmp	0b
+
+.data
+idt_ptr:
+	.short 0x3ff
+	.long 0x0

kernel/proc.c

@@ -356,6 +356,8 @@ check_misc_flags:
 	 */
 	p->p_misc_flags &= ~MF_CONTEXT_SET;
 
+  	assert(!(p->p_misc_flags & MF_FULLVM) || p->p_seg.p_cr3 != 0);
+	refresh_tlb();
 	/*
 	 * restore_user_context() carries out the actual mode switch from kernel
 	 * to userspace. This function does not return