SMP - reduced TLB flushing

- flush TLB of processes only if the page tables has been changed and
  the page tables of this process are already loaded on this cpu which
  means that there might be stale entries in TLB. Until now SMP was
  always flushing TLB to make sure everything is consistent.

kernel/arch/i386/klib.S

@@ -803,11 +803,9 @@ ENTRY(__switch_address_space)
 	 * test if the cr3 is loaded with the current value to avoid unnecessary
 	 * TLB flushes
 	 */
-#ifndef CONFIG_SMP
 	mov	%cr3, %ecx
 	cmp	%ecx, %eax
 	je	0f
-#endif
 	mov	%eax, %cr3
 	/* get ptproc */
 	mov	8(%esp), %eax

kernel/proc.c

@@ -242,6 +242,9 @@ PUBLIC void switch_to_user(void)
 	 * to be scheduled again.
 	 */
 	struct proc * p;
+#ifdef CONFIG_SMP
+	int tlb_must_refresh = 0;
+#endif
 
 	p = get_cpulocal_var(proc_ptr);
 	/*
@@ -279,6 +282,10 @@ not_runnable_pick_new:
 	/* update the global variable */
 	get_cpulocal_var(proc_ptr) = p;
 
+#ifdef CONFIG_SMP
+	if (p->p_misc_flags & MF_FLUSH_TLB && get_cpulocal_var(ptproc) == p)
+		tlb_must_refresh = 1;
+#endif
 	switch_address_space(p);
 
 check_misc_flags:
@@ -385,7 +392,11 @@ check_misc_flags:
 
   	assert(!(p->p_misc_flags & MF_FULLVM) || p->p_seg.p_cr3 != 0);
 #ifdef CONFIG_SMP
-	refresh_tlb();
+	if (p->p_misc_flags & MF_FLUSH_TLB) {
+		if (tlb_must_refresh)
+			refresh_tlb();
+		p->p_misc_flags &= ~MF_FLUSH_TLB;
+	}
 #endif
 	
 	restart_local_timer();

kernel/proc.h

@@ -242,6 +242,9 @@ struct proc {
 #define MF_SENDING_FROM_KERNEL	0x2000 /* message of this process is from kernel */
 #define MF_CONTEXT_SET	0x4000 /* don't touch context */
 #define MF_SPROF_SEEN	0x8000 /* profiling has seen this process */
+#define MF_FLUSH_TLB	0x10000	/* if set, TLB must be flushed before letting
+				   this process run again. Currently it only
+				   applies to SMP */
 
 /* Magic process table addresses. */
 #define BEG_PROC_ADDR (&proc[0])

kernel/system/do_vmctl.c

@@ -148,6 +148,9 @@ PUBLIC int do_vmctl(struct proc * caller, message * m_ptr)
 		} else
 #endif
 			RTS_SET(p, RTS_VMINHIBIT);
+#if CONFIG_SMP
+		p->p_misc_flags |= MF_FLUSH_TLB;
+#endif
 		return OK;
 	case VMCTL_VMINHIBIT_CLEAR:
 		assert(RTS_ISSET(p, RTS_VMINHIBIT));