atomicity fix when enabling paging

- before enabling paging VM asks kernel to resize its segments. This
  may cause kernel to segfault if APIC is used and an interrupt
  happens between this and paging enabled. As these are 2 separate
  vmctl calls it is not atomic. This patch fixes this problem. VM does
  not ask kernel to resize the segments in a separate call anymore.
  The new segments limit is part of the "enable paging" call. It
  generalizes this call in such a way that more information can be
  passed as need be or the information may be completely different if
  another architecture requires this.

servers/vm/i386/pagetable.c

@@ -639,7 +639,7 @@ PUBLIC void pt_init(phys_bytes usedlimit)
 	int global_bit_ok = 0;
 	int free_pde;
 	int p;
-	vir_bytes kernlimit;
+	struct vm_ep_data ep_data;
 	vir_bytes sparepages_mem;
 	phys_bytes sparepages_ph;
 
@@ -803,13 +803,6 @@ PUBLIC void pt_init(phys_bytes usedlimit)
 	/* first pde in use by process. */
 	proc_pde = free_pde;
 
-	kernlimit = free_pde*I386_BIG_PAGE_SIZE;
-
-	/* Increase kernel segment to address this memory. */
-	if((r=sys_vmctl(SELF, VMCTL_I386_KERNELLIMIT, kernlimit)) != OK) {
-                panic("VMCTL_I386_KERNELLIMIT failed: %d", r);
-	}
-
 	kpagedir = arch_map2vir(&vmproc[VMP_SYSTEM],
 		pagedir_pde*I386_BIG_PAGE_SIZE);
 
@@ -822,8 +815,13 @@ PUBLIC void pt_init(phys_bytes usedlimit)
 	pt_mapkernel(newpt);	/* didn't know about vm_dir pages earlier */
         pt_bind(newpt, vmp);
        
+	/* new segment limit for the kernel after paging is enabled */
+	ep_data.data_seg_limit = free_pde*I386_BIG_PAGE_SIZE;
+	/* the memory map which must be installed after paging is enabled */
+	ep_data.mem_map = vmp->vm_arch.vm_seg;
+
 	/* Now actually enable paging. */
-	if(sys_vmctl_enable_paging(vmp->vm_arch.vm_seg) != OK)
+	if(sys_vmctl_enable_paging(&ep_data) != OK)
         	panic("pt_init: enable paging failed");
 
         /* Back to reality - this is where the stack actually is. */