freebsd-src/sys/vm/vm_glue.c

/*-
 * SPDX-License-Identifier: (BSD-3-Clause AND MIT-CMU)
 *
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */

#include <sys/cdefs.h>
#include "opt_vm.h"
#include "opt_kstack_pages.h"
#include "opt_kstack_max_pages.h"
#include "opt_kstack_usage_prof.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/asan.h>
#include <sys/domainset.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/msan.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/racct.h>
#include <sys/refcount.h>
#include <sys/resourcevar.h>
#include <sys/rwlock.h>
#include <sys/sched.h>
#include <sys/sf_buf.h>
#include <sys/shm.h>
#include <sys/smp.h>
#include <sys/vmmeter.h>
#include <sys/vmem.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/unistd.h>

#include <vm/uma.h>
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#include <vm/vm_domainset.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pagequeue.h>
#include <vm/vm_object.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/vm_pager.h>
#include <vm/swap_pager.h>
#include <vm/vm_phys.h>

#include <machine/cpu.h>

#if VM_NRESERVLEVEL > 0
#define KVA_KSTACK_QUANTUM_SHIFT (VM_LEVEL_0_ORDER + PAGE_SHIFT)
#else
#define KVA_KSTACK_QUANTUM_SHIFT (8 + PAGE_SHIFT)
#endif
#define KVA_KSTACK_QUANTUM (1ul << KVA_KSTACK_QUANTUM_SHIFT)

/*
 * MPSAFE
 *
 * WARNING!  This code calls vm_map_check_protection() which only checks
 * the associated vm_map_entry range.  It does not determine whether the
 * contents of the memory is actually readable or writable.  In most cases
 * just checking the vm_map_entry is sufficient within the kernel's address
 * space.
 */
bool
kernacc(void *addr, int len, int rw)
{
	boolean_t rv;
	vm_offset_t saddr, eaddr;
	vm_prot_t prot;

	KASSERT((rw & ~VM_PROT_ALL) == 0,
	    ("illegal ``rw'' argument to kernacc (%x)\n", rw));

	if ((vm_offset_t)addr + len > vm_map_max(kernel_map) ||
	    (vm_offset_t)addr + len < (vm_offset_t)addr)
		return (false);

	prot = rw;
	saddr = trunc_page((vm_offset_t)addr);
	eaddr = round_page((vm_offset_t)addr + len);
	vm_map_lock_read(kernel_map);
	rv = vm_map_check_protection(kernel_map, saddr, eaddr, prot);
	vm_map_unlock_read(kernel_map);
	return (rv == TRUE);
}

/*
 * MPSAFE
 *
 * WARNING!  This code calls vm_map_check_protection() which only checks
 * the associated vm_map_entry range.  It does not determine whether the
 * contents of the memory is actually readable or writable.  vmapbuf(),
 * vm_fault_quick(), or copyin()/copout()/su*()/fu*() functions should be
 * used in conjunction with this call.
 */
bool
useracc(void *addr, int len, int rw)
{
	boolean_t rv;
	vm_prot_t prot;
	vm_map_t map;

	KASSERT((rw & ~VM_PROT_ALL) == 0,
	    ("illegal ``rw'' argument to useracc (%x)\n", rw));
	prot = rw;
	map = &curproc->p_vmspace->vm_map;
	if ((vm_offset_t)addr + len > vm_map_max(map) ||
	    (vm_offset_t)addr + len < (vm_offset_t)addr) {
		return (false);
	}
	vm_map_lock_read(map);
	rv = vm_map_check_protection(map, trunc_page((vm_offset_t)addr),
	    round_page((vm_offset_t)addr + len), prot);
	vm_map_unlock_read(map);
	return (rv == TRUE);
}

int
vslock(void *addr, size_t len)
{
	vm_offset_t end, last, start;
	vm_size_t npages;
	int error;

	last = (vm_offset_t)addr + len;
	start = trunc_page((vm_offset_t)addr);
	end = round_page(last);
	if (last < (vm_offset_t)addr || end < (vm_offset_t)addr)
		return (EINVAL);
	npages = atop(end - start);
	if (npages > vm_page_max_user_wired)
		return (ENOMEM);
	error = vm_map_wire(&curproc->p_vmspace->vm_map, start, end,
	    VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
	if (error == KERN_SUCCESS) {
		curthread->td_vslock_sz += len;
		return (0);
	}

	/*
	 * Return EFAULT on error to match copy{in,out}() behaviour
	 * rather than returning ENOMEM like mlock() would.
	 */
	return (EFAULT);
}

void
vsunlock(void *addr, size_t len)
{

	/* Rely on the parameter sanity checks performed by vslock(). */
	MPASS(curthread->td_vslock_sz >= len);
	curthread->td_vslock_sz -= len;
	(void)vm_map_unwire(&curproc->p_vmspace->vm_map,
	    trunc_page((vm_offset_t)addr), round_page((vm_offset_t)addr + len),
	    VM_MAP_WIRE_SYSTEM | VM_MAP_WIRE_NOHOLES);
}

/*
 * Pin the page contained within the given object at the given offset.  If the
 * page is not resident, allocate and load it using the given object's pager.
 * Return the pinned page if successful; otherwise, return NULL.
 */
static vm_page_t
vm_imgact_hold_page(vm_object_t object, vm_ooffset_t offset)
{
	vm_page_t m;
	vm_pindex_t pindex;

	pindex = OFF_TO_IDX(offset);
	(void)vm_page_grab_valid_unlocked(&m, object, pindex,
	    VM_ALLOC_NORMAL | VM_ALLOC_NOBUSY | VM_ALLOC_WIRED);
	return (m);
}

/*
 * Return a CPU private mapping to the page at the given offset within the
 * given object.  The page is pinned before it is mapped.
 */
struct sf_buf *
vm_imgact_map_page(vm_object_t object, vm_ooffset_t offset)
{
	vm_page_t m;

	m = vm_imgact_hold_page(object, offset);
	if (m == NULL)
		return (NULL);
	sched_pin();
	return (sf_buf_alloc(m, SFB_CPUPRIVATE));
}

/*
 * Destroy the given CPU private mapping and unpin the page that it mapped.
 */
void
vm_imgact_unmap_page(struct sf_buf *sf)
{
	vm_page_t m;

	m = sf_buf_page(sf);
	sf_buf_free(sf);
	sched_unpin();
	vm_page_unwire(m, PQ_ACTIVE);
}

void
vm_sync_icache(vm_map_t map, vm_offset_t va, vm_offset_t sz)
{

	pmap_sync_icache(map->pmap, va, sz);
}

static vm_object_t kstack_object;
static vm_object_t kstack_alt_object;
static uma_zone_t kstack_cache;
static int kstack_cache_size;
static vmem_t *vmd_kstack_arena[MAXMEMDOM];

static int
sysctl_kstack_cache_size(SYSCTL_HANDLER_ARGS)
{
	int error, oldsize;

	oldsize = kstack_cache_size;
	error = sysctl_handle_int(oidp, arg1, arg2, req);
	if (error == 0 && req->newptr && oldsize != kstack_cache_size)
		uma_zone_set_maxcache(kstack_cache, kstack_cache_size);
	return (error);
}
SYSCTL_PROC(_vm, OID_AUTO, kstack_cache_size,
    CTLTYPE_INT|CTLFLAG_MPSAFE|CTLFLAG_RW, &kstack_cache_size, 0,
    sysctl_kstack_cache_size, "IU", "Maximum number of cached kernel stacks");

/*
 *	Allocate a virtual address range from a domain kstack arena, following
 *	the specified NUMA policy.
 */
static vm_offset_t
vm_thread_alloc_kstack_kva(vm_size_t size, int domain)
{
#ifndef __ILP32__
	int rv;
	vmem_t *arena;
	vm_offset_t addr = 0;

	size = round_page(size);
	/* Allocate from the kernel arena for non-standard kstack sizes. */
	if (size != ptoa(kstack_pages + KSTACK_GUARD_PAGES)) {
		arena = vm_dom[domain].vmd_kernel_arena;
	} else {
		arena = vmd_kstack_arena[domain];
	}
	rv = vmem_alloc(arena, size, M_BESTFIT | M_NOWAIT, &addr);
	if (rv == ENOMEM)
		return (0);
	KASSERT(atop(addr - VM_MIN_KERNEL_ADDRESS) %
	    (kstack_pages + KSTACK_GUARD_PAGES) == 0,
	    ("%s: allocated kstack KVA not aligned to multiple of kstack size",
	    __func__));

	return (addr);
#else
	return (kva_alloc(size));
#endif
}

/*
 *	Release a region of kernel virtual memory
 *	allocated from the kstack arena.
 */
static __noinline void
vm_thread_free_kstack_kva(vm_offset_t addr, vm_size_t size, int domain)
{
	vmem_t *arena;

	size = round_page(size);
#ifdef __ILP32__
	arena = kernel_arena;
#else
	arena = vmd_kstack_arena[domain];
	if (size != ptoa(kstack_pages + KSTACK_GUARD_PAGES)) {
		arena = vm_dom[domain].vmd_kernel_arena;
	}
#endif
	vmem_free(arena, addr, size);
}

static vmem_size_t
vm_thread_kstack_import_quantum(void)
{
#ifndef __ILP32__
	/*
	 * The kstack_quantum is larger than KVA_QUANTUM to account
	 * for holes induced by guard pages.
	 */
	return (KVA_KSTACK_QUANTUM * (kstack_pages + KSTACK_GUARD_PAGES));
#else
	return (KVA_KSTACK_QUANTUM);
#endif
}

/*
 * Import KVA from a parent arena into the kstack arena. Imports must be
 * a multiple of kernel stack pages + guard pages in size.
 *
 * Kstack VA allocations need to be aligned so that the linear KVA pindex
 * is divisible by the total number of kstack VA pages. This is necessary to
 * make vm_kstack_pindex work properly.
 *
 * We import a multiple of KVA_KSTACK_QUANTUM-sized region from the parent
 * arena. The actual size used by the kstack arena is one kstack smaller to
 * allow for the necessary alignment adjustments to be made.
 */
static int
vm_thread_kstack_arena_import(void *arena, vmem_size_t size, int flags,
    vmem_addr_t *addrp)
{
	int error, rem;
	size_t kpages = kstack_pages + KSTACK_GUARD_PAGES;

	KASSERT(atop(size) % kpages == 0,
	    ("%s: Size %jd is not a multiple of kstack pages (%d)", __func__,
	    (intmax_t)size, (int)kpages));

	error = vmem_xalloc(arena, vm_thread_kstack_import_quantum(),
	    KVA_KSTACK_QUANTUM, 0, 0, VMEM_ADDR_MIN, VMEM_ADDR_MAX, flags,
	    addrp);
	if (error) {
		return (error);
	}

	rem = atop(*addrp - VM_MIN_KERNEL_ADDRESS) % kpages;
	if (rem != 0) {
		/* Bump addr to next aligned address */
		*addrp = *addrp + (kpages - rem) * PAGE_SIZE;
	}

	return (0);
}

/*
 * Release KVA from a parent arena into the kstack arena. Released imports must
 * be a multiple of kernel stack pages + guard pages in size.
 */
static void
vm_thread_kstack_arena_release(void *arena, vmem_addr_t addr, vmem_size_t size)
{
	int rem;
	size_t kpages __diagused = kstack_pages + KSTACK_GUARD_PAGES;

	KASSERT(size % kpages == 0,
	    ("%s: Size %jd is not a multiple of kstack pages (%d)", __func__,
	    (intmax_t)size, (int)kpages));

	KASSERT((addr - VM_MIN_KERNEL_ADDRESS) % kpages == 0,
	    ("%s: Address %p is not properly aligned (%p)", __func__,
		(void *)addr, (void *)VM_MIN_KERNEL_ADDRESS));
	/*
	 * If the address is not KVA_KSTACK_QUANTUM-aligned we have to decrement
	 * it to account for the shift in kva_import_kstack.
	 */
	rem = addr % KVA_KSTACK_QUANTUM;
	if (rem) {
		KASSERT(rem <= ptoa(kpages),
		    ("%s: rem > kpages (%d), (%d)", __func__, rem,
			(int)kpages));
		addr -= rem;
	}
	vmem_xfree(arena, addr, vm_thread_kstack_import_quantum());
}

/*
 * Create the kernel stack for a new thread.
 */
static vm_offset_t
vm_thread_stack_create(struct domainset *ds, int pages)
{
	vm_page_t ma[KSTACK_MAX_PAGES];
	struct vm_domainset_iter di;
	int req = VM_ALLOC_NORMAL;
	vm_object_t obj;
	vm_offset_t ks;
	int domain, i;

	obj = vm_thread_kstack_size_to_obj(pages);
	if (vm_ndomains > 1)
		obj->domain.dr_policy = ds;
	vm_domainset_iter_page_init(&di, obj, 0, &domain, &req);
	do {
		/*
		 * Get a kernel virtual address for this thread's kstack.
		 */
		ks = vm_thread_alloc_kstack_kva(ptoa(pages + KSTACK_GUARD_PAGES),
		    domain);
		if (ks == 0)
			continue;
		ks += ptoa(KSTACK_GUARD_PAGES);

		/*
		 * Allocate physical pages to back the stack.
		 */
		if (vm_thread_stack_back(ks, ma, pages, req, domain) != 0) {
			vm_thread_free_kstack_kva(ks - ptoa(KSTACK_GUARD_PAGES),
			    ptoa(pages + KSTACK_GUARD_PAGES), domain);
			continue;
		}
		if (KSTACK_GUARD_PAGES != 0) {
			pmap_qremove(ks - ptoa(KSTACK_GUARD_PAGES),
			    KSTACK_GUARD_PAGES);
		}
		for (i = 0; i < pages; i++)
			vm_page_valid(ma[i]);
		pmap_qenter(ks, ma, pages);
		return (ks);
	} while (vm_domainset_iter_page(&di, obj, &domain) == 0);

	return (0);
}

static __noinline void
vm_thread_stack_dispose(vm_offset_t ks, int pages)
{
	vm_page_t m;
	vm_pindex_t pindex;
	int i, domain;
	vm_object_t obj = vm_thread_kstack_size_to_obj(pages);

	pindex = vm_kstack_pindex(ks, pages);
	domain = vm_phys_domain(vtophys(ks));
	pmap_qremove(ks, pages);
	VM_OBJECT_WLOCK(obj);
	for (i = 0; i < pages; i++) {
		m = vm_page_lookup(obj, pindex + i);
		if (m == NULL)
			panic("%s: kstack already missing?", __func__);
		KASSERT(vm_page_domain(m) == domain,
		    ("%s: page %p domain mismatch, expected %d got %d",
		    __func__, m, domain, vm_page_domain(m)));
		vm_page_xbusy_claim(m);
		vm_page_unwire_noq(m);
		vm_page_free(m);
	}
	VM_OBJECT_WUNLOCK(obj);
	kasan_mark((void *)ks, ptoa(pages), ptoa(pages), 0);
	vm_thread_free_kstack_kva(ks - (KSTACK_GUARD_PAGES * PAGE_SIZE),
	    ptoa(pages + KSTACK_GUARD_PAGES), domain);
}

/*
 * Allocate the kernel stack for a new thread.
 */
int
vm_thread_new(struct thread *td, int pages)
{
	vm_offset_t ks;
	u_short ks_domain;

	/* Bounds check */
	if (pages <= 1)
		pages = kstack_pages;
	else if (pages > KSTACK_MAX_PAGES)
		pages = KSTACK_MAX_PAGES;

	ks = 0;
	if (pages == kstack_pages && kstack_cache != NULL)
		ks = (vm_offset_t)uma_zalloc(kstack_cache, M_NOWAIT);

	/*
	 * Ensure that kstack objects can draw pages from any memory
	 * domain.  Otherwise a local memory shortage can block a process
	 * swap-in.
	 */
	if (ks == 0)
		ks = vm_thread_stack_create(DOMAINSET_PREF(PCPU_GET(domain)),
		    pages);
	if (ks == 0)
		return (0);

	ks_domain = vm_phys_domain(vtophys(ks));
	KASSERT(ks_domain >= 0 && ks_domain < vm_ndomains,
	    ("%s: invalid domain for kstack %p", __func__, (void *)ks));
	td->td_kstack = ks;
	td->td_kstack_pages = pages;
	td->td_kstack_domain = ks_domain;
	return (1);
}

/*
 * Dispose of a thread's kernel stack.
 */
void
vm_thread_dispose(struct thread *td)
{
	vm_offset_t ks;
	int pages;

	pages = td->td_kstack_pages;
	ks = td->td_kstack;
	td->td_kstack = 0;
	td->td_kstack_pages = 0;
	td->td_kstack_domain = MAXMEMDOM;
	if (pages == kstack_pages) {
		kasan_mark((void *)ks, 0, ptoa(pages), KASAN_KSTACK_FREED);
		uma_zfree(kstack_cache, (void *)ks);
	} else {
		vm_thread_stack_dispose(ks, pages);
	}
}

/*
 * Calculate kstack pindex.
 *
 * Uses a non-identity mapping if guard pages are
 * active to avoid pindex holes in the kstack object.
 */
vm_pindex_t
vm_kstack_pindex(vm_offset_t ks, int kpages)
{
	vm_pindex_t pindex = atop(ks - VM_MIN_KERNEL_ADDRESS);

#ifdef __ILP32__
	return (pindex);
#else
	/*
	 * Return the linear pindex if guard pages aren't active or if we are
	 * allocating a non-standard kstack size.
	 */
	if (KSTACK_GUARD_PAGES == 0 || kpages != kstack_pages) {
		return (pindex);
	}
	KASSERT(pindex % (kpages + KSTACK_GUARD_PAGES) >= KSTACK_GUARD_PAGES,
	    ("%s: Attempting to calculate kstack guard page pindex", __func__));

	return (pindex -
	    (pindex / (kpages + KSTACK_GUARD_PAGES) + 1) * KSTACK_GUARD_PAGES);
#endif
}

/*
 * Allocate physical pages, following the specified NUMA policy, to back a
 * kernel stack.
 */
int
vm_thread_stack_back(vm_offset_t ks, vm_page_t ma[], int npages, int req_class,
    int domain)
{
	vm_object_t obj = vm_thread_kstack_size_to_obj(npages);
	vm_pindex_t pindex;
	vm_page_t m;
	int n;

	pindex = vm_kstack_pindex(ks, npages);

	VM_OBJECT_WLOCK(obj);
	for (n = 0; n < npages;) {
		m = vm_page_grab(obj, pindex + n,
		    VM_ALLOC_NOCREAT | VM_ALLOC_WIRED);
		if (m == NULL) {
			m = vm_page_alloc_domain(obj, pindex + n, domain,
			    req_class | VM_ALLOC_WIRED);
		}
		if (m == NULL)
			break;
		ma[n++] = m;
	}
	if (n < npages)
		goto cleanup;
	VM_OBJECT_WUNLOCK(obj);

	return (0);
cleanup:
	for (int i = 0; i < n; i++) {
		m = ma[i];
		(void)vm_page_unwire_noq(m);
		vm_page_free(m);
	}
	VM_OBJECT_WUNLOCK(obj);

	return (ENOMEM);
}

vm_object_t
vm_thread_kstack_size_to_obj(int npages)
{
	return (npages == kstack_pages ? kstack_object : kstack_alt_object);
}

static int
kstack_import(void *arg, void **store, int cnt, int domain, int flags)
{
	struct domainset *ds;
	int i;

	if (domain == UMA_ANYDOMAIN)
		ds = DOMAINSET_RR();
	else
		ds = DOMAINSET_PREF(domain);

	for (i = 0; i < cnt; i++) {
		store[i] = (void *)vm_thread_stack_create(ds, kstack_pages);
		if (store[i] == NULL)
			break;
	}
	return (i);
}

static void
kstack_release(void *arg, void **store, int cnt)
{
	vm_offset_t ks;
	int i;

	for (i = 0; i < cnt; i++) {
		ks = (vm_offset_t)store[i];
		vm_thread_stack_dispose(ks, kstack_pages);
	}
}

static void
kstack_cache_init(void *null)
{
	vm_size_t kstack_quantum;
	int domain;

	kstack_object = vm_object_allocate(OBJT_SWAP,
	    atop(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS));
	kstack_cache = uma_zcache_create("kstack_cache",
	    kstack_pages * PAGE_SIZE, NULL, NULL, NULL, NULL,
	    kstack_import, kstack_release, NULL,
	    UMA_ZONE_FIRSTTOUCH);
	kstack_cache_size = imax(128, mp_ncpus * 4);
	uma_zone_set_maxcache(kstack_cache, kstack_cache_size);

	kstack_alt_object = vm_object_allocate(OBJT_SWAP,
	    atop(VM_MAX_KERNEL_ADDRESS - VM_MIN_KERNEL_ADDRESS));

	kstack_quantum = vm_thread_kstack_import_quantum();
	/*
	 * Reduce size used by the kstack arena to allow for
	 * alignment adjustments in vm_thread_kstack_arena_import.
	 */
	kstack_quantum -= (kstack_pages + KSTACK_GUARD_PAGES) * PAGE_SIZE;
	/*
	 * Create the kstack_arena for each domain and set kernel_arena as
	 * parent.
	 */
	for (domain = 0; domain < vm_ndomains; domain++) {
		vmd_kstack_arena[domain] = vmem_create("kstack arena", 0, 0,
		    PAGE_SIZE, 0, M_WAITOK);
		KASSERT(vmd_kstack_arena[domain] != NULL,
		    ("%s: failed to create domain %d kstack_arena", __func__,
		    domain));
		vmem_set_import(vmd_kstack_arena[domain],
		    vm_thread_kstack_arena_import,
		    vm_thread_kstack_arena_release,
		    vm_dom[domain].vmd_kernel_arena, kstack_quantum);
	}
}
SYSINIT(vm_kstacks, SI_SUB_KMEM, SI_ORDER_ANY, kstack_cache_init, NULL);

#ifdef KSTACK_USAGE_PROF
/*
 * Track maximum stack used by a thread in kernel.
 */
static int max_kstack_used;

SYSCTL_INT(_debug, OID_AUTO, max_kstack_used, CTLFLAG_RD,
    &max_kstack_used, 0,
    "Maximum stack depth used by a thread in kernel");

void
intr_prof_stack_use(struct thread *td, struct trapframe *frame)
{
	vm_offset_t stack_top;
	vm_offset_t current;
	int used, prev_used;

	/*
	 * Testing for interrupted kernel mode isn't strictly
	 * needed. It optimizes the execution, since interrupts from
	 * usermode will have only the trap frame on the stack.
	 */
	if (TRAPF_USERMODE(frame))
		return;

	stack_top = td->td_kstack + td->td_kstack_pages * PAGE_SIZE;
	current = (vm_offset_t)(uintptr_t)&stack_top;

	/*
	 * Try to detect if interrupt is using kernel thread stack.
	 * Hardware could use a dedicated stack for interrupt handling.
	 */
	if (stack_top <= current || current < td->td_kstack)
		return;

	used = stack_top - current;
	for (;;) {
		prev_used = max_kstack_used;
		if (prev_used >= used)
			break;
		if (atomic_cmpset_int(&max_kstack_used, prev_used, used))
			break;
	}
}
#endif /* KSTACK_USAGE_PROF */

/*
 * Implement fork's actions on an address space.
 * Here we arrange for the address space to be copied or referenced,
 * allocate a user struct (pcb and kernel stack), then call the
 * machine-dependent layer to fill those in and make the new process
 * ready to run.  The new process is set up so that it returns directly
 * to user mode to avoid stack copying and relocation problems.
 */
int
vm_forkproc(struct thread *td, struct proc *p2, struct thread *td2,
    struct vmspace *vm2, int flags)
{
	struct proc *p1 = td->td_proc;
	struct domainset *dset;
	int error;

	if ((flags & RFPROC) == 0) {
		/*
		 * Divorce the memory, if it is shared, essentially
		 * this changes shared memory amongst threads, into
		 * COW locally.
		 */
		if ((flags & RFMEM) == 0) {
			error = vmspace_unshare(p1);
			if (error)
				return (error);
		}
		cpu_fork(td, p2, td2, flags);
		return (0);
	}

	if (flags & RFMEM) {
		p2->p_vmspace = p1->p_vmspace;
		refcount_acquire(&p1->p_vmspace->vm_refcnt);
	}
	dset = td2->td_domain.dr_policy;
	while (vm_page_count_severe_set(&dset->ds_mask)) {
		vm_wait_doms(&dset->ds_mask, 0);
	}

	if ((flags & RFMEM) == 0) {
		p2->p_vmspace = vm2;
		if (p1->p_vmspace->vm_shm)
			shmfork(p1, p2);
	}

	/*
	 * cpu_fork will copy and update the pcb, set up the kernel stack,
	 * and make the child ready to run.
	 */
	cpu_fork(td, p2, td2, flags);
	return (0);
}

/*
 * Called after process has been wait(2)'ed upon and is being reaped.
 * The idea is to reclaim resources that we could not reclaim while
 * the process was still executing.
 */
void
vm_waitproc(struct proc *p)
{

	vmspace_exitfree(p);		/* and clean-out the vmspace */
}

void
kick_proc0(void)
{

	wakeup(&proc0);
}