Refine the change in rev 1.125: the UVM mitigation for CoW faulting

when multiple CPUs are running threads in the process is only needed
when there can be multiple CPUs, so save a fault on SP builds.

ok miod@ mpi@

diff --git a/sys/uvm/uvm_fault.c b/sys/uvm/uvm_fault.c
index 9f5da3f..87d8252 100644 (file)
--- a/sys/uvm/uvm_fault.c
+++ b/sys/uvm/uvm_fault.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: uvm_fault.c,v 1.131 2022/06/28 10:45:55 mpi Exp $     */
+/*     $OpenBSD: uvm_fault.c,v 1.132 2022/08/31 01:27:04 guenther Exp $        */
 /*     $NetBSD: uvm_fault.c,v 1.51 2000/08/06 00:22:53 thorpej Exp $   */
 
 /*
@@ -1023,13 +1023,14 @@ uvm_fault_upper(struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
                /* deref: can not drop to zero here by defn! */
                oanon->an_ref--;
 
-#ifndef __HAVE_PMAP_MPSAFE_ENTER_COW
+#if defined(MULTIPROCESSOR) && !defined(__HAVE_PMAP_MPSAFE_ENTER_COW)
                /*
                 * If there are multiple threads, either uvm or the
                 * pmap has to make sure no threads see the old RO
                 * mapping once any have seen the new RW mapping.
                 * uvm does it by inserting the new mapping RO and
                 * letting it fault again.
+                * This is only a problem on MP systems.
                 */
                if (P_HASSIBLING(curproc)) {
                        flt->enter_prot &= ~PROT_WRITE;