diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -10256,6 +10256,12 @@
 	PCPU_SET(ucr3, PMAP_NO_CR3);
 }
 
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	*res = pmap->pm_active;
+}
+
 void
 pmap_sync_icache(pmap_t pm, vm_offset_t va, vm_size_t sz)
 {
diff --git a/sys/arm/arm/pmap-v6.c b/sys/arm/arm/pmap-v6.c
--- a/sys/arm/arm/pmap-v6.c
+++ b/sys/arm/arm/pmap-v6.c
@@ -6194,6 +6194,12 @@
 	critical_exit();
 }
 
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	*res = pmap->pm_active;
+}
+
 /*
  * Perform the pmap work for mincore(2).  If the page is not both referenced and
  * modified by this pmap, returns its physical address so that the caller can
diff --git a/sys/arm64/include/pmap.h b/sys/arm64/include/pmap.h
--- a/sys/arm64/include/pmap.h
+++ b/sys/arm64/include/pmap.h
@@ -129,6 +129,8 @@
 	(uint64_t)(asid) << TTBR_ASID_SHIFT;			\
 })
 
+#define	PMAP_WANT_ACTIVE_CPUS_NAIVE
+
 extern vm_offset_t virtual_avail;
 extern vm_offset_t virtual_end;
 
diff --git a/sys/i386/i386/pmap_base.c b/sys/i386/i386/pmap_base.c
--- a/sys/i386/i386/pmap_base.c
+++ b/sys/i386/i386/pmap_base.c
@@ -944,6 +944,12 @@
 	pmap_methods_ptr->pm_kremove(va);
 }
 
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	*res = pmap->pm_active;
+}
+
 extern struct pmap_methods pmap_pae_methods, pmap_nopae_methods;
 int pae_mode;
 SYSCTL_INT(_vm_pmap, OID_AUTO, pae_mode, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
diff --git a/sys/powerpc/powerpc/pmap_dispatch.c b/sys/powerpc/powerpc/pmap_dispatch.c
--- a/sys/powerpc/powerpc/pmap_dispatch.c
+++ b/sys/powerpc/powerpc/pmap_dispatch.c
@@ -253,3 +253,9 @@
 		return (FALSE);
 	}
 }
+
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	*res = pmap->pm_active;
+}
diff --git a/sys/riscv/riscv/pmap.c b/sys/riscv/riscv/pmap.c
--- a/sys/riscv/riscv/pmap.c
+++ b/sys/riscv/riscv/pmap.c
@@ -4687,6 +4687,12 @@
 	PCPU_SET(curpmap, pmap);
 }
 
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	*res = pmap->pm_active;
+}
+
 void
 pmap_sync_icache(pmap_t pmap, vm_offset_t va, vm_size_t sz)
 {
diff --git a/sys/vm/pmap.h b/sys/vm/pmap.h
--- a/sys/vm/pmap.h
+++ b/sys/vm/pmap.h
@@ -90,6 +90,7 @@
 #include <machine/pmap.h>
 
 #ifdef _KERNEL
+#include <sys/_cpuset.h>
 struct thread;
 
 /*
@@ -118,6 +119,7 @@
 #define	PMAP_TS_REFERENCED_MAX	5
 
 void		 pmap_activate(struct thread *td);
+void		 pmap_active_cpus(pmap_t pmap, cpuset_t *res);
 void		 pmap_advise(pmap_t pmap, vm_offset_t sva, vm_offset_t eva,
 		    int advice);
 void		 pmap_align_superpage(vm_object_t, vm_ooffset_t, vm_offset_t *,
diff --git a/sys/vm/vm_kern.c b/sys/vm/vm_kern.c
--- a/sys/vm/vm_kern.c
+++ b/sys/vm/vm_kern.c
@@ -78,6 +78,7 @@
 #include <sys/msan.h>
 #include <sys/proc.h>
 #include <sys/rwlock.h>
+#include <sys/smp.h>
 #include <sys/sysctl.h>
 #include <sys/vmem.h>
 #include <sys/vmmeter.h>
@@ -907,6 +908,31 @@
 #endif
 }
 
+#ifdef PMAP_WANT_ACTIVE_CPUS_NAIVE
+void
+pmap_active_cpus(pmap_t pmap, cpuset_t *res)
+{
+	struct thread *td;
+	struct proc *p;
+	struct vmspace *vm;
+	int c;
+
+	CPU_ZERO(res);
+	CPU_FOREACH(c) {
+		td = cpuid_to_pcpu[c]->pc_curthread;
+		p = td->td_proc;
+		if (p == NULL)
+			continue;
+		vm = vmspace_acquire_ref(p);
+		if (vm == NULL)
+			continue;
+		if (pmap == vmspace_pmap(vm))
+			CPU_SET(c, res);
+		vmspace_free(vm);
+	}
+}
+#endif
+
 /*
  * Allow userspace to directly trigger the VM drain routine for testing
  * purposes.