From: guenther <guenther@openbsd.org>
Date: Wed, 31 Aug 2022 01:27:04 +0000 (+0000)
Subject: Refine the change in rev 1.125: the UVM mitigation for CoW faulting
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=2f953554c5a9e915642f6a83021903c37d5c84aa;p=openbsd

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 9f5da3ff047..87d8252f936 100644
--- 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;