--- /sys/src/9k/k10/mem.h
+++ /sys/src/9k/k10/mem.h
@@ -104,3 +104,6 @@
 
 /* this can go when the arguments to mmuput change */
 #define PPN(x)		((x) & ~(PGSZ-1))		/* GAK */
+
+#define	KVATOP	(KSEG0&KSEG1&KSEG2)
+#define	iskaddr(a)	(((uintptr)(a)&KVATOP) == KVATOP)
--- /sys/src/9k/port/chan.c
+++ /sys/src/9k/port/chan.c
@@ -1604,7 +1604,7 @@ validname0(char *aname, int slashok, int dup, uintptr pc)
 	Rune r;
 
 	name = aname;
-	if((PTR2UINT(name) & KZERO) != KZERO){		/* hmmmm */
+	if(!iskaddr(name)){
 		if(!dup)
 			print("warning: validname* called from %#p with user pointer", pc);
 		ename = vmemchr(name, 0, (1<<16));
--- /sys/src/9k/port/devaoe.c
+++ /sys/src/9k/port/devaoe.c
@@ -1157,8 +1157,6 @@ strategy(Aoedev *d, Srb *srb)
 	poperror();
 }
 
-#define iskaddr(a)	((uintptr)(a) > KZERO)
-
 static long
 rw(Aoedev *d, int write, uchar *db, long len, uvlong off)
 {
--- /sys/src/9k/port/devproc.c
+++ /sys/src/9k/port/devproc.c
@@ -755,7 +755,7 @@ procread(Chan *c, void *va, long n, vlong off)
 		return readstr(offset, va, n, p->syscalltrace);
 
 	case Qmem:
-		if(offset < KZERO
+		if(!iskaddr(offset)
 		|| (offset >= USTKTOP-USTKSIZE && offset < USTKTOP)){
 			r = procctlmemio(p, offset, n, va, 1);
 			psdecref(p);
--- /sys/src/9k/port/fault.c
+++ /sys/src/9k/port/fault.c
@@ -315,7 +315,7 @@ vmemchr(void *s, int c, int n)
 			return t;
 		a += r;
 		n -= r;
-		if(a < KZERO)
+		if(!iskaddr(a))
 			validaddr(UINT2PTR(a), 1, 0);
 	}
 
--- /sys/src/9k/port/sysseg.c
+++ /sys/src/9k/port/sysseg.c
@@ -190,7 +190,7 @@ segattach(Proc* p, int attr, char* name, uintptr va, usize len)
 	uintptr pgsize;
 
 	/* BUG: Only ok for now */
-	if((va != 0 && va < UTZERO) || (va & KZERO) == KZERO)
+	if((va != 0 && va < UTZERO) || iskaddr(va))
 		error("virtual address in kernel");
 
 	vmemchr(name, 0, ~0);