diff --git a/sys/arch/arm/include/arm32/pmap.h b/sys/arch/arm/include/arm32/pmap.h
index 8af5d63a72da..117b67540e82 100644
--- a/sys/arch/arm/include/arm32/pmap.h
+++ b/sys/arch/arm/include/arm32/pmap.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: pmap.h,v 1.19 2001/11/23 19:21:48 thorpej Exp $	*/
+/*	$NetBSD: pmap.h,v 1.20 2002/01/19 16:55:22 chs Exp $	*/
 
 /*
  * Copyright (c) 1994,1995 Mark Brinicombe.
@@ -211,6 +211,12 @@ boolean_t	pmap_pageidlezero __P((paddr_t));
 #define KERNEL_PD_SIZE	\
 	(PD_SIZE - (KERNEL_SPACE_START >> PDSHIFT) * sizeof(pd_entry_t))
 
+/*
+ * tell MI code that the cache is virtually-indexed *and* virtually-tagged.
+ */
+
+#define PMAP_CACHE_VIVT
+
 #endif /* _KERNEL */
 
 #endif	/* _ARM32_PMAP_H_ */
diff --git a/sys/uvm/uvm_bio.c b/sys/uvm/uvm_bio.c
index f21e8ad09b6d..cdca7fe61695 100644
--- a/sys/uvm/uvm_bio.c
+++ b/sys/uvm/uvm_bio.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: uvm_bio.c,v 1.22 2001/11/19 02:44:27 enami Exp $	*/
+/*	$NetBSD: uvm_bio.c,v 1.23 2002/01/19 16:55:20 chs Exp $	*/
 
 /*
  * Copyright (c) 1998 Chuck Silvers.
@@ -34,7 +34,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.22 2001/11/19 02:44:27 enami Exp $");
+__KERNEL_RCSID(0, "$NetBSD: uvm_bio.c,v 1.23 2002/01/19 16:55:20 chs Exp $");
 
 #include "opt_uvmhist.h"
 
@@ -229,6 +229,7 @@ ubc_fault(ufi, ign1, ign2, ign3, ign4, fault_type, access_type, flags)
 	vaddr_t va, eva, ubc_offset, slot_offset;
 	int i, error, npages;
 	struct vm_page *pgs[ubc_winsize >> PAGE_SHIFT], *pg;
+	vm_prot_t prot;
 	UVMHIST_FUNC("ubc_fault");  UVMHIST_CALLED(ubchist);
 
 	/*
@@ -288,6 +289,18 @@ again:
 	va = ufi->orig_rvaddr;
 	eva = ufi->orig_rvaddr + (npages << PAGE_SHIFT);
 
+	/*
+	 * for virtually-indexed, virtually-tagged caches we should avoid
+	 * creating writable mappings when we don't absolutely need them,
+	 * since the "compatible alias" trick doesn't work on such caches.
+	 * otherwise, we can always map the pages writable.
+	 */
+
+#ifdef PMAP_CACHE_VIVT
+	prot = VM_PROT_READ | access_type;
+#else
+	prot = VM_PROT_READ | VM_PROT_WRITE;
+#endif
 	UVMHIST_LOG(ubchist, "va 0x%lx eva 0x%lx", va, eva, 0,0);
 	simple_lock(&uobj->vmobjlock);
 	uvm_lock_pageq();
@@ -309,7 +322,7 @@ again:
 		KASSERT(access_type == VM_PROT_READ ||
 		    (pg->flags & PG_RDONLY) == 0);
 		pmap_enter(ufi->orig_map->pmap, va, VM_PAGE_TO_PHYS(pg),
-		    VM_PROT_READ | VM_PROT_WRITE, access_type);
+		    prot, access_type);
 		uvm_pageactivate(pg);
 		pg->flags &= ~(PG_BUSY);
 		UVM_PAGE_OWN(pg, NULL);