o Call vm_map_growstack() from vm_fault() if vm_map_lookup() has failed

due to conditions that suggest the possible need for stack growth.
   This has two beneficial effects: (1) we can
   now remove calls to vm_map_growstack() from the MD trap handlers and (2)
   simple page faults are faster because we no longer unnecessarily perform
   vm_map_growstack() on every page fault.
 o Remove vm_map_growstack() from the i386's trap_pfault().
 o Remove the acquisition and release of Giant from i386's trap_pfault().
   (vm_fault() still acquires it.)

sys/amd64/amd64/trap.c

@@ -703,7 +703,6 @@ trap_pfault(frame, usermode, eva)
 	else
 		ftype = VM_PROT_READ;
 
-	mtx_lock(&Giant);
 	if (map != kernel_map) {
 		/*
 		 * Keep swapout from messing with us during this
@@ -713,20 +712,8 @@ trap_pfault(frame, usermode, eva)
 		++p->p_lock;
 		PROC_UNLOCK(p);
 
-		/*
+		/* Fault in the user page: */
-		 * Grow the stack if necessary
+		rv = vm_fault(map, va, ftype,
-		 */
-		/* vm_map_growstack fails only if va falls into
-		 * a growable stack region and the stack growth
-		 * fails.  It succeeds if va was not within
-		 * a growable stack region, or if the stack 
-		 * growth succeeded.
-		 */
-		if (vm_map_growstack(p, va) != KERN_SUCCESS)
-			rv = KERN_FAILURE;
-		else
-			/* Fault in the user page: */
-			rv = vm_fault(map, va, ftype,
 			      (ftype & VM_PROT_WRITE) ? VM_FAULT_DIRTY
 						      : VM_FAULT_NORMAL);
 
@@ -740,8 +727,6 @@ trap_pfault(frame, usermode, eva)
 		 */
 		rv = vm_fault(map, va, ftype, VM_FAULT_NORMAL);
 	}
-	mtx_unlock(&Giant);
-
 	if (rv == KERN_SUCCESS)
 		return (0);
 nogo:

sys/i386/i386/trap.c

@@ -703,7 +703,6 @@ trap_pfault(frame, usermode, eva)
 	else
 		ftype = VM_PROT_READ;
 
-	mtx_lock(&Giant);
 	if (map != kernel_map) {
 		/*
 		 * Keep swapout from messing with us during this
@@ -713,20 +712,8 @@ trap_pfault(frame, usermode, eva)
 		++p->p_lock;
 		PROC_UNLOCK(p);
 
-		/*
+		/* Fault in the user page: */
-		 * Grow the stack if necessary
+		rv = vm_fault(map, va, ftype,
-		 */
-		/* vm_map_growstack fails only if va falls into
-		 * a growable stack region and the stack growth
-		 * fails.  It succeeds if va was not within
-		 * a growable stack region, or if the stack 
-		 * growth succeeded.
-		 */
-		if (vm_map_growstack(p, va) != KERN_SUCCESS)
-			rv = KERN_FAILURE;
-		else
-			/* Fault in the user page: */
-			rv = vm_fault(map, va, ftype,
 			      (ftype & VM_PROT_WRITE) ? VM_FAULT_DIRTY
 						      : VM_FAULT_NORMAL);
 
@@ -740,8 +727,6 @@ trap_pfault(frame, usermode, eva)
 		 */
 		rv = vm_fault(map, va, ftype, VM_FAULT_NORMAL);
 	}
-	mtx_unlock(&Giant);
-
 	if (rv == KERN_SUCCESS)
 		return (0);
 nogo:

sys/vm/vm_fault.c

@@ -203,7 +203,7 @@ vm_fault1(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 {
 	vm_prot_t prot;
 	int result;
-	boolean_t wired;
+	boolean_t growstack, wired;
 	int map_generation;
 	vm_object_t next_object;
 	vm_page_t marray[VM_FAULT_READ];
@@ -215,6 +215,7 @@ vm_fault1(vm_map_t map, vm_offset_t vaddr, vm_prot_t fault_type,
 
 	cnt.v_vm_faults++;
 	hardfault = 0;
+	growstack = TRUE;
 
 RetryFault:;
 
@@ -228,6 +229,14 @@ RetryFault:;
 		&fs.first_pindex, &prot, &wired)) != KERN_SUCCESS) {
 		if ((result != KERN_PROTECTION_FAILURE) ||
 			((fault_flags & VM_FAULT_WIRE_MASK) != VM_FAULT_USER_WIRE)) {
+			if (growstack && result == KERN_INVALID_ADDRESS &&
+			    map != kernel_map && curproc != NULL) {
+				result = vm_map_growstack(curproc, vaddr);
+				if (result != KERN_SUCCESS)
+					return (KERN_FAILURE);
+				growstack = FALSE;
+				goto RetryFault;
+			}
 			return result;
 		}