Index: svs.c
===================================================================
RCS file: /cvsroot/src/sys/arch/x86/x86/svs.c,v
retrieving revision 1.35
diff -u -p -r1.35 svs.c
--- svs.c	2 May 2020 11:37:17 -0000	1.35
+++ svs.c	19 May 2020 22:47:34 -0000
@@ -1,7 +1,7 @@
 /*	$NetBSD: svs.c,v 1.35 2020/05/02 11:37:17 maxv Exp $	*/
 
 /*
- * Copyright (c) 2018-2019 The NetBSD Foundation, Inc.
+ * Copyright (c) 2018-2020 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -575,6 +575,18 @@ svs_pmap_sync(struct pmap *pmap, int ind
 	KASSERT(kpreempt_disabled());
 	KASSERT(index < PDIR_SLOT_USERLIM);
 
+	ci = curcpu();
+	cid = cpu_index(ci);
+
+	mutex_enter(&ci->ci_svs_mtx);
+	KASSERT(kcpuset_isset(pmap->pm_kernel_cpus, cid));
+	ci->ci_svs_updir[index] = pmap->pm_pdir[index];
+	mutex_exit(&ci->ci_svs_mtx);
+
+	if (!kcpuset_isotherset(pmap->pm_kernel_cpus, cid)) {
+		return;
+	}
+
 	for (CPU_INFO_FOREACH(cii, ci)) {
 		cid = cpu_index(ci);
 
@@ -670,28 +682,16 @@ svs_lwp_switch(struct lwp *oldlwp, struc
 	}
 }
 
-static inline pt_entry_t
-svs_pte_atomic_read(struct pmap *pmap, size_t idx)
-{
-	/*
-	 * XXX: We don't have a basic atomic_fetch_64 function?
-	 */
-	return atomic_cas_64(&pmap->pm_pdir[idx], 666, 666);
-}
-
 /*
- * We may come here with the pmap unlocked. So read its PTEs atomically. If
- * a remote CPU is updating them at the same time, it's not a problem: the
- * remote CPU will call svs_pmap_sync afterwards, and our updirpa will be
- * synchronized properly.
+ * We may come here with the pmap unlocked.  If a remote CPU is updating
+ * them at the same time, it's not a problem: the remote CPU will call
+ * svs_pmap_sync afterwards, and our updirpa will be synchronized properly.
  */
 void
 svs_pdir_switch(struct pmap *pmap)
 {
 	struct cpu_info *ci = curcpu();
 	struct svs_utls *utls;
-	pt_entry_t pte;
-	size_t i;
 
 	KASSERT(kpreempt_disabled());
 	KASSERT(pmap != pmap_kernel());
@@ -700,14 +700,10 @@ svs_pdir_switch(struct pmap *pmap)
 	utls = (struct svs_utls *)ci->ci_svs_utls;
 	utls->kpdirpa = pmap_pdirpa(pmap, 0) | svs_pcid_kcr3;
 
+	/* Copy user slots. */
 	mutex_enter(&ci->ci_svs_mtx);
-
-	/* User slots. */
-	for (i = 0; i < PDIR_SLOT_USERLIM; i++) {
-		pte = svs_pte_atomic_read(pmap, i);
-		ci->ci_svs_updir[i] = pte;
-	}
-
+	memcpy(ci->ci_svs_updir, pmap->pm_pdir, PDIR_SLOT_USERLIM *
+	    sizeof(pt_entry_t));
 	mutex_exit(&ci->ci_svs_mtx);
 
 	if (svs_pcid) {