FreeBSD/Linux Kernel Cross Reference
sys/vm/vm_kern.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.
     *
     *      from: @(#)vm_kern.c     8.3 (Berkeley) 1/12/94
     *
     *
     * Copyright (c) 1987, 1990 Carnegie-Mellon University.
     * All rights reserved.
     *
     * Authors: Avadis Tevanian, Jr., Michael Wayne Young
     *
     * 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.
     */
    
    /*
     *      Kernel memory management.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>         /* for ticks and hz */
    #include <sys/domainset.h>
    #include <sys/eventhandler.h>
    #include <sys/lock.h>
    #include <sys/proc.h>
    #include <sys/malloc.h>
    #include <sys/rwlock.h>
    #include <sys/sysctl.h>
    #include <sys/vmem.h>
    #include <sys/vmmeter.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_domainset.h>
    #include <vm/vm_kern.h>
    #include <vm/pmap.h>
    #include <vm/vm_map.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pageout.h>
    #include <vm/vm_pagequeue.h>
    #include <vm/vm_phys.h>
    #include <vm/vm_radix.h>
    #include <vm/vm_extern.h>
    #include <vm/uma.h>
    
   struct vm_map kernel_map_store;
   struct vm_map exec_map_store;
   struct vm_map pipe_map_store;
   
   const void *zero_region;
   CTASSERT((ZERO_REGION_SIZE & PAGE_MASK) == 0);
   
   /* NB: Used by kernel debuggers. */
   const u_long vm_maxuser_address = VM_MAXUSER_ADDRESS;
   
   u_int exec_map_entry_size;
   u_int exec_map_entries;
   
   SYSCTL_ULONG(_vm, OID_AUTO, min_kernel_address, CTLFLAG_RD,
       SYSCTL_NULL_ULONG_PTR, VM_MIN_KERNEL_ADDRESS, "Min kernel address");
   
   SYSCTL_ULONG(_vm, OID_AUTO, max_kernel_address, CTLFLAG_RD,
   #if defined(__arm__)
       &vm_max_kernel_address, 0,
   #else
       SYSCTL_NULL_ULONG_PTR, VM_MAX_KERNEL_ADDRESS,
   #endif
       "Max kernel address");
   
   #if VM_NRESERVLEVEL > 0
   #define KVA_QUANTUM_SHIFT       (VM_LEVEL_0_ORDER + PAGE_SHIFT)
   #else
   /* On non-superpage architectures we want large import sizes. */
   #define KVA_QUANTUM_SHIFT       (8 + PAGE_SHIFT)
   #endif
   #define KVA_QUANTUM             (1ul << KVA_QUANTUM_SHIFT)
   #define KVA_NUMA_IMPORT_QUANTUM (KVA_QUANTUM * 128)
   
   extern void     uma_startup2(void);
   
   /*
    *      kva_alloc:
    *
    *      Allocate a virtual address range with no underlying object and
    *      no initial mapping to physical memory.  Any mapping from this
    *      range to physical memory must be explicitly created prior to
    *      its use, typically with pmap_qenter().  Any attempt to create
    *      a mapping on demand through vm_fault() will result in a panic. 
    */
   vm_offset_t
   kva_alloc(vm_size_t size)
   {
           vm_offset_t addr;
   
           size = round_page(size);
           if (vmem_alloc(kernel_arena, size, M_BESTFIT | M_NOWAIT, &addr))
                   return (0);
   
           return (addr);
   }
   
   /*
    *      kva_free:
    *
    *      Release a region of kernel virtual memory allocated
    *      with kva_alloc, and return the physical pages
    *      associated with that region.
    *
    *      This routine may not block on kernel maps.
    */
   void
   kva_free(vm_offset_t addr, vm_size_t size)
   {
   
           size = round_page(size);
           vmem_free(kernel_arena, addr, size);
   }
   
   static vm_page_t
   kmem_alloc_contig_pages(vm_object_t object, vm_pindex_t pindex, int domain,
       int pflags, u_long npages, vm_paddr_t low, vm_paddr_t high,
       u_long alignment, vm_paddr_t boundary, vm_memattr_t memattr)
   {
           vm_page_t m;
           int tries;
           bool wait;
   
           VM_OBJECT_ASSERT_WLOCKED(object);
   
           wait = (pflags & VM_ALLOC_WAITOK) != 0;
           pflags &= ~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL);
           pflags |= VM_ALLOC_NOWAIT;
           for (tries = wait ? 3 : 1;; tries--) {
                   m = vm_page_alloc_contig_domain(object, pindex, domain, pflags,
                       npages, low, high, alignment, boundary, memattr);
                   if (m != NULL || tries == 0)
                           break;
   
                   VM_OBJECT_WUNLOCK(object);
                   if (!vm_page_reclaim_contig_domain(domain, pflags, npages,
                       low, high, alignment, boundary) && wait)
                           vm_wait_domain(domain);
                   VM_OBJECT_WLOCK(object);
           }
           return (m);
   }
   
   /*
    *      Allocates a region from the kernel address map and physical pages
    *      within the specified address range to the kernel object.  Creates a
    *      wired mapping from this region to these pages, and returns the
    *      region's starting virtual address.  The allocated pages are not
    *      necessarily physically contiguous.  If M_ZERO is specified through the
    *      given flags, then the pages are zeroed before they are mapped.
    */
   static vm_offset_t
   kmem_alloc_attr_domain(int domain, vm_size_t size, int flags, vm_paddr_t low,
       vm_paddr_t high, vm_memattr_t memattr)
   {
           vmem_t *vmem;
           vm_object_t object;
           vm_offset_t addr, i, offset;
           vm_page_t m;
           int pflags;
           vm_prot_t prot;
   
           object = kernel_object;
           size = round_page(size);
           vmem = vm_dom[domain].vmd_kernel_arena;
           if (vmem_alloc(vmem, size, M_BESTFIT | flags, &addr))
                   return (0);
           offset = addr - VM_MIN_KERNEL_ADDRESS;
           pflags = malloc2vm_flags(flags) | VM_ALLOC_WIRED;
           prot = (flags & M_EXEC) != 0 ? VM_PROT_ALL : VM_PROT_RW;
           VM_OBJECT_WLOCK(object);
           for (i = 0; i < size; i += PAGE_SIZE) {
                   m = kmem_alloc_contig_pages(object, atop(offset + i),
                       domain, pflags, 1, low, high, PAGE_SIZE, 0, memattr);
                   if (m == NULL) {
                           VM_OBJECT_WUNLOCK(object);
                           kmem_unback(object, addr, i);
                           vmem_free(vmem, addr, size);
                           return (0);
                   }
                   KASSERT(vm_page_domain(m) == domain,
                       ("kmem_alloc_attr_domain: Domain mismatch %d != %d",
                       vm_page_domain(m), domain));
                   if ((flags & M_ZERO) && (m->flags & PG_ZERO) == 0)
                           pmap_zero_page(m);
                   vm_page_valid(m);
                   pmap_enter(kernel_pmap, addr + i, m, prot,
                       prot | PMAP_ENTER_WIRED, 0);
           }
           VM_OBJECT_WUNLOCK(object);
           return (addr);
   }
   
   vm_offset_t
   kmem_alloc_attr(vm_size_t size, int flags, vm_paddr_t low, vm_paddr_t high,
       vm_memattr_t memattr)
   {
   
           return (kmem_alloc_attr_domainset(DOMAINSET_RR(), size, flags, low,
               high, memattr));
   }
   
   vm_offset_t
   kmem_alloc_attr_domainset(struct domainset *ds, vm_size_t size, int flags,
       vm_paddr_t low, vm_paddr_t high, vm_memattr_t memattr)
   {
           struct vm_domainset_iter di;
           vm_offset_t addr;
           int domain;
   
           vm_domainset_iter_policy_init(&di, ds, &domain, &flags);
           do {
                   addr = kmem_alloc_attr_domain(domain, size, flags, low, high,
                       memattr);
                   if (addr != 0)
                           break;
           } while (vm_domainset_iter_policy(&di, &domain) == 0);
   
           return (addr);
   }
   
   /*
    *      Allocates a region from the kernel address map and physically
    *      contiguous pages within the specified address range to the kernel
    *      object.  Creates a wired mapping from this region to these pages, and
    *      returns the region's starting virtual address.  If M_ZERO is specified
    *      through the given flags, then the pages are zeroed before they are
    *      mapped.
    */
   static vm_offset_t
   kmem_alloc_contig_domain(int domain, vm_size_t size, int flags, vm_paddr_t low,
       vm_paddr_t high, u_long alignment, vm_paddr_t boundary,
       vm_memattr_t memattr)
   {
           vmem_t *vmem;
           vm_object_t object;
           vm_offset_t addr, offset, tmp;
           vm_page_t end_m, m;
           u_long npages;
           int pflags;
   
           object = kernel_object;
           size = round_page(size);
           vmem = vm_dom[domain].vmd_kernel_arena;
           if (vmem_alloc(vmem, size, flags | M_BESTFIT, &addr))
                   return (0);
           offset = addr - VM_MIN_KERNEL_ADDRESS;
           pflags = malloc2vm_flags(flags) | VM_ALLOC_WIRED;
           npages = atop(size);
           VM_OBJECT_WLOCK(object);
           m = kmem_alloc_contig_pages(object, atop(offset), domain,
               pflags, npages, low, high, alignment, boundary, memattr);
           if (m == NULL) {
                   VM_OBJECT_WUNLOCK(object);
                   vmem_free(vmem, addr, size);
                   return (0);
           }
           KASSERT(vm_page_domain(m) == domain,
               ("kmem_alloc_contig_domain: Domain mismatch %d != %d",
               vm_page_domain(m), domain));
           end_m = m + npages;
           tmp = addr;
           for (; m < end_m; m++) {
                   if ((flags & M_ZERO) && (m->flags & PG_ZERO) == 0)
                           pmap_zero_page(m);
                   vm_page_valid(m);
                   pmap_enter(kernel_pmap, tmp, m, VM_PROT_RW,
                       VM_PROT_RW | PMAP_ENTER_WIRED, 0);
                   tmp += PAGE_SIZE;
           }
           VM_OBJECT_WUNLOCK(object);
           return (addr);
   }
   
   vm_offset_t
   kmem_alloc_contig(vm_size_t size, int flags, vm_paddr_t low, vm_paddr_t high,
       u_long alignment, vm_paddr_t boundary, vm_memattr_t memattr)
   {
   
           return (kmem_alloc_contig_domainset(DOMAINSET_RR(), size, flags, low,
               high, alignment, boundary, memattr));
   }
   
   vm_offset_t
   kmem_alloc_contig_domainset(struct domainset *ds, vm_size_t size, int flags,
       vm_paddr_t low, vm_paddr_t high, u_long alignment, vm_paddr_t boundary,
       vm_memattr_t memattr)
   {
           struct vm_domainset_iter di;
           vm_offset_t addr;
           int domain;
   
           vm_domainset_iter_policy_init(&di, ds, &domain, &flags);
           do {
                   addr = kmem_alloc_contig_domain(domain, size, flags, low, high,
                       alignment, boundary, memattr);
                   if (addr != 0)
                           break;
           } while (vm_domainset_iter_policy(&di, &domain) == 0);
   
           return (addr);
   }
   
   /*
    *      kmem_subinit:
    *
    *      Initializes a map to manage a subrange
    *      of the kernel virtual address space.
    *
    *      Arguments are as follows:
    *
    *      parent          Map to take range from
    *      min, max        Returned endpoints of map
    *      size            Size of range to find
    *      superpage_align Request that min is superpage aligned
    */
   void
   kmem_subinit(vm_map_t map, vm_map_t parent, vm_offset_t *min, vm_offset_t *max,
       vm_size_t size, bool superpage_align)
   {
           int ret;
   
           size = round_page(size);
   
           *min = vm_map_min(parent);
           ret = vm_map_find(parent, NULL, 0, min, size, 0, superpage_align ?
               VMFS_SUPER_SPACE : VMFS_ANY_SPACE, VM_PROT_ALL, VM_PROT_ALL,
               MAP_ACC_NO_CHARGE);
           if (ret != KERN_SUCCESS)
                   panic("kmem_subinit: bad status return of %d", ret);
           *max = *min + size;
           vm_map_init(map, vm_map_pmap(parent), *min, *max);
           if (vm_map_submap(parent, *min, *max, map) != KERN_SUCCESS)
                   panic("kmem_subinit: unable to change range to submap");
   }
   
   /*
    *      kmem_malloc_domain:
    *
    *      Allocate wired-down pages in the kernel's address space.
    */
   static vm_offset_t
   kmem_malloc_domain(int domain, vm_size_t size, int flags)
   {
           vmem_t *arena;
           vm_offset_t addr;
           int rv;
   
           if (__predict_true((flags & M_EXEC) == 0))
                   arena = vm_dom[domain].vmd_kernel_arena;
           else
                   arena = vm_dom[domain].vmd_kernel_rwx_arena;
           size = round_page(size);
           if (vmem_alloc(arena, size, flags | M_BESTFIT, &addr))
                   return (0);
   
           rv = kmem_back_domain(domain, kernel_object, addr, size, flags);
           if (rv != KERN_SUCCESS) {
                   vmem_free(arena, addr, size);
                   return (0);
           }
           return (addr);
   }
   
   vm_offset_t
   kmem_malloc(vm_size_t size, int flags)
   {
   
           return (kmem_malloc_domainset(DOMAINSET_RR(), size, flags));
   }
   
   vm_offset_t
   kmem_malloc_domainset(struct domainset *ds, vm_size_t size, int flags)
   {
           struct vm_domainset_iter di;
           vm_offset_t addr;
           int domain;
   
           vm_domainset_iter_policy_init(&di, ds, &domain, &flags);
           do {
                   addr = kmem_malloc_domain(domain, size, flags);
                   if (addr != 0)
                           break;
           } while (vm_domainset_iter_policy(&di, &domain) == 0);
   
           return (addr);
   }
   
   /*
    *      kmem_back_domain:
    *
    *      Allocate physical pages from the specified domain for the specified
    *      virtual address range.
    */
   int
   kmem_back_domain(int domain, vm_object_t object, vm_offset_t addr,
       vm_size_t size, int flags)
   {
           vm_offset_t offset, i;
           vm_page_t m, mpred;
           vm_prot_t prot;
           int pflags;
   
           KASSERT(object == kernel_object,
               ("kmem_back_domain: only supports kernel object."));
   
           offset = addr - VM_MIN_KERNEL_ADDRESS;
           pflags = malloc2vm_flags(flags) | VM_ALLOC_WIRED;
           pflags &= ~(VM_ALLOC_NOWAIT | VM_ALLOC_WAITOK | VM_ALLOC_WAITFAIL);
           if (flags & M_WAITOK)
                   pflags |= VM_ALLOC_WAITFAIL;
           prot = (flags & M_EXEC) != 0 ? VM_PROT_ALL : VM_PROT_RW;
   
           i = 0;
           VM_OBJECT_WLOCK(object);
   retry:
           mpred = vm_radix_lookup_le(&object->rtree, atop(offset + i));
           for (; i < size; i += PAGE_SIZE, mpred = m) {
                   m = vm_page_alloc_domain_after(object, atop(offset + i),
                       domain, pflags, mpred);
   
                   /*
                    * Ran out of space, free everything up and return. Don't need
                    * to lock page queues here as we know that the pages we got
                    * aren't on any queues.
                    */
                   if (m == NULL) {
                           if ((flags & M_NOWAIT) == 0)
                                   goto retry;
                           VM_OBJECT_WUNLOCK(object);
                           kmem_unback(object, addr, i);
                           return (KERN_NO_SPACE);
                   }
                   KASSERT(vm_page_domain(m) == domain,
                       ("kmem_back_domain: Domain mismatch %d != %d",
                       vm_page_domain(m), domain));
                   if (flags & M_ZERO && (m->flags & PG_ZERO) == 0)
                           pmap_zero_page(m);
                   KASSERT((m->oflags & VPO_UNMANAGED) != 0,
                       ("kmem_malloc: page %p is managed", m));
                   vm_page_valid(m);
                   pmap_enter(kernel_pmap, addr + i, m, prot,
                       prot | PMAP_ENTER_WIRED, 0);
                   if (__predict_false((prot & VM_PROT_EXECUTE) != 0))
                           m->oflags |= VPO_KMEM_EXEC;
           }
           VM_OBJECT_WUNLOCK(object);
   
           return (KERN_SUCCESS);
   }
   
   /*
    *      kmem_back:
    *
    *      Allocate physical pages for the specified virtual address range.
    */
   int
   kmem_back(vm_object_t object, vm_offset_t addr, vm_size_t size, int flags)
   {
           vm_offset_t end, next, start;
           int domain, rv;
   
           KASSERT(object == kernel_object,
               ("kmem_back: only supports kernel object."));
   
           for (start = addr, end = addr + size; addr < end; addr = next) {
                   /*
                    * We must ensure that pages backing a given large virtual page
                    * all come from the same physical domain.
                    */
                   if (vm_ndomains > 1) {
                           domain = (addr >> KVA_QUANTUM_SHIFT) % vm_ndomains;
                           while (VM_DOMAIN_EMPTY(domain))
                                   domain++;
                           next = roundup2(addr + 1, KVA_QUANTUM);
                           if (next > end || next < start)
                                   next = end;
                   } else {
                           domain = 0;
                           next = end;
                   }
                   rv = kmem_back_domain(domain, object, addr, next - addr, flags);
                   if (rv != KERN_SUCCESS) {
                           kmem_unback(object, start, addr - start);
                           break;
                   }
           }
           return (rv);
   }
   
   /*
    *      kmem_unback:
    *
    *      Unmap and free the physical pages underlying the specified virtual
    *      address range.
    *
    *      A physical page must exist within the specified object at each index
    *      that is being unmapped.
    */
   static struct vmem *
   _kmem_unback(vm_object_t object, vm_offset_t addr, vm_size_t size)
   {
           struct vmem *arena;
           vm_page_t m, next;
           vm_offset_t end, offset;
           int domain;
   
           KASSERT(object == kernel_object,
               ("kmem_unback: only supports kernel object."));
   
           if (size == 0)
                   return (NULL);
           pmap_remove(kernel_pmap, addr, addr + size);
           offset = addr - VM_MIN_KERNEL_ADDRESS;
           end = offset + size;
           VM_OBJECT_WLOCK(object);
           m = vm_page_lookup(object, atop(offset)); 
           domain = vm_page_domain(m);
           if (__predict_true((m->oflags & VPO_KMEM_EXEC) == 0))
                   arena = vm_dom[domain].vmd_kernel_arena;
           else
                   arena = vm_dom[domain].vmd_kernel_rwx_arena;
           for (; offset < end; offset += PAGE_SIZE, m = next) {
                   next = vm_page_next(m);
                   vm_page_xbusy_claim(m);
                   vm_page_unwire_noq(m);
                   vm_page_free(m);
           }
           VM_OBJECT_WUNLOCK(object);
   
           return (arena);
   }
   
   void
   kmem_unback(vm_object_t object, vm_offset_t addr, vm_size_t size)
   {
   
           (void)_kmem_unback(object, addr, size);
   }
   
   /*
    *      kmem_free:
    *
    *      Free memory allocated with kmem_malloc.  The size must match the
    *      original allocation.
    */
   void
   kmem_free(vm_offset_t addr, vm_size_t size)
   {
           struct vmem *arena;
   
           size = round_page(size);
           arena = _kmem_unback(kernel_object, addr, size);
           if (arena != NULL)
                   vmem_free(arena, addr, size);
   }
   
   /*
    *      kmap_alloc_wait:
    *
    *      Allocates pageable memory from a sub-map of the kernel.  If the submap
    *      has no room, the caller sleeps waiting for more memory in the submap.
    *
    *      This routine may block.
    */
   vm_offset_t
   kmap_alloc_wait(vm_map_t map, vm_size_t size)
   {
           vm_offset_t addr;
   
           size = round_page(size);
           if (!swap_reserve(size))
                   return (0);
   
           for (;;) {
                   /*
                    * To make this work for more than one map, use the map's lock
                    * to lock out sleepers/wakers.
                    */
                   vm_map_lock(map);
                   addr = vm_map_findspace(map, vm_map_min(map), size);
                   if (addr + size <= vm_map_max(map))
                           break;
                   /* no space now; see if we can ever get space */
                   if (vm_map_max(map) - vm_map_min(map) < size) {
                           vm_map_unlock(map);
                           swap_release(size);
                           return (0);
                   }
                   map->needs_wakeup = TRUE;
                   vm_map_unlock_and_wait(map, 0);
           }
           vm_map_insert(map, NULL, 0, addr, addr + size, VM_PROT_RW, VM_PROT_RW,
               MAP_ACC_CHARGED);
           vm_map_unlock(map);
           return (addr);
   }
   
   /*
    *      kmap_free_wakeup:
    *
    *      Returns memory to a submap of the kernel, and wakes up any processes
    *      waiting for memory in that map.
    */
   void
   kmap_free_wakeup(vm_map_t map, vm_offset_t addr, vm_size_t size)
   {
   
           vm_map_lock(map);
           (void) vm_map_delete(map, trunc_page(addr), round_page(addr + size));
           if (map->needs_wakeup) {
                   map->needs_wakeup = FALSE;
                   vm_map_wakeup(map);
           }
           vm_map_unlock(map);
   }
   
   void
   kmem_init_zero_region(void)
   {
           vm_offset_t addr, i;
           vm_page_t m;
   
           /*
            * Map a single physical page of zeros to a larger virtual range.
            * This requires less looping in places that want large amounts of
            * zeros, while not using much more physical resources.
            */
           addr = kva_alloc(ZERO_REGION_SIZE);
           m = vm_page_alloc(NULL, 0, VM_ALLOC_NORMAL |
               VM_ALLOC_NOOBJ | VM_ALLOC_WIRED | VM_ALLOC_ZERO);
           if ((m->flags & PG_ZERO) == 0)
                   pmap_zero_page(m);
           for (i = 0; i < ZERO_REGION_SIZE; i += PAGE_SIZE)
                   pmap_qenter(addr + i, &m, 1);
           pmap_protect(kernel_pmap, addr, addr + ZERO_REGION_SIZE, VM_PROT_READ);
   
           zero_region = (const void *)addr;
   }
   
   /*
    * Import KVA from the kernel map into the kernel arena.
    */
   static int
   kva_import(void *unused, vmem_size_t size, int flags, vmem_addr_t *addrp)
   {
           vm_offset_t addr;
           int result;
   
           KASSERT((size % KVA_QUANTUM) == 0,
               ("kva_import: Size %jd is not a multiple of %d",
               (intmax_t)size, (int)KVA_QUANTUM));
           addr = vm_map_min(kernel_map);
           result = vm_map_find(kernel_map, NULL, 0, &addr, size, 0,
               VMFS_SUPER_SPACE, VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);
           if (result != KERN_SUCCESS)
                   return (ENOMEM);
   
           *addrp = addr;
   
           return (0);
   }
   
   /*
    * Import KVA from a parent arena into a per-domain arena.  Imports must be
    * KVA_QUANTUM-aligned and a multiple of KVA_QUANTUM in size.
    */
   static int
   kva_import_domain(void *arena, vmem_size_t size, int flags, vmem_addr_t *addrp)
   {
   
           KASSERT((size % KVA_QUANTUM) == 0,
               ("kva_import_domain: Size %jd is not a multiple of %d",
               (intmax_t)size, (int)KVA_QUANTUM));
           return (vmem_xalloc(arena, size, KVA_QUANTUM, 0, 0, VMEM_ADDR_MIN,
               VMEM_ADDR_MAX, flags, addrp));
   }
   
   /*
    *      kmem_init:
    *
    *      Create the kernel map; insert a mapping covering kernel text, 
    *      data, bss, and all space allocated thus far (`boostrap' data).  The 
    *      new map will thus map the range between VM_MIN_KERNEL_ADDRESS and 
    *      `start' as allocated, and the range between `start' and `end' as free.
    *      Create the kernel vmem arena and its per-domain children.
    */
   void
   kmem_init(vm_offset_t start, vm_offset_t end)
   {
           vm_size_t quantum;
           int domain;
   
           vm_map_init(kernel_map, kernel_pmap, VM_MIN_KERNEL_ADDRESS, end);
           kernel_map->system_map = 1;
           vm_map_lock(kernel_map);
           /* N.B.: cannot use kgdb to debug, starting with this assignment ... */
           (void)vm_map_insert(kernel_map, NULL, 0,
   #ifdef __amd64__
               KERNBASE,
   #else                
               VM_MIN_KERNEL_ADDRESS,
   #endif
               start, VM_PROT_ALL, VM_PROT_ALL, MAP_NOFAULT);
           /* ... and ending with the completion of the above `insert' */
   
   #ifdef __amd64__
           /*
            * Mark KVA used for the page array as allocated.  Other platforms
            * that handle vm_page_array allocation can simply adjust virtual_avail
            * instead.
            */
           (void)vm_map_insert(kernel_map, NULL, 0, (vm_offset_t)vm_page_array,
               (vm_offset_t)vm_page_array + round_2mpage(vm_page_array_size *
               sizeof(struct vm_page)),
               VM_PROT_RW, VM_PROT_RW, MAP_NOFAULT);
   #endif
           vm_map_unlock(kernel_map);
   
           /*
            * Use a large import quantum on NUMA systems.  This helps minimize
            * interleaving of superpages, reducing internal fragmentation within
            * the per-domain arenas.
            */
           if (vm_ndomains > 1 && PMAP_HAS_DMAP)
                   quantum = KVA_NUMA_IMPORT_QUANTUM;
           else
                   quantum = KVA_QUANTUM;
   
           /*
            * Initialize the kernel_arena.  This can grow on demand.
            */
           vmem_init(kernel_arena, "kernel arena", 0, 0, PAGE_SIZE, 0, 0);
           vmem_set_import(kernel_arena, kva_import, NULL, NULL, quantum);
   
           for (domain = 0; domain < vm_ndomains; domain++) {
                   /*
                    * Initialize the per-domain arenas.  These are used to color
                    * the KVA space in a way that ensures that virtual large pages
                    * are backed by memory from the same physical domain,
                    * maximizing the potential for superpage promotion.
                    */
                   vm_dom[domain].vmd_kernel_arena = vmem_create(
                       "kernel arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
                   vmem_set_import(vm_dom[domain].vmd_kernel_arena,
                       kva_import_domain, NULL, kernel_arena, quantum);
   
                   /*
                    * In architectures with superpages, maintain separate arenas
                    * for allocations with permissions that differ from the
                    * "standard" read/write permissions used for kernel memory,
                    * so as not to inhibit superpage promotion.
                    *
                    * Use the base import quantum since this arena is rarely used.
                    */
   #if VM_NRESERVLEVEL > 0
                   vm_dom[domain].vmd_kernel_rwx_arena = vmem_create(
                       "kernel rwx arena domain", 0, 0, PAGE_SIZE, 0, M_WAITOK);
                   vmem_set_import(vm_dom[domain].vmd_kernel_rwx_arena,
                       kva_import_domain, (vmem_release_t *)vmem_xfree,
                       kernel_arena, KVA_QUANTUM);
   #else
                   vm_dom[domain].vmd_kernel_rwx_arena =
                       vm_dom[domain].vmd_kernel_arena;
   #endif
           }
   
           /*
            * This must be the very first call so that the virtual address
            * space used for early allocations is properly marked used in
            * the map.
            */
           uma_startup2();
   }
   
   /*
    *      kmem_bootstrap_free:
    *
    *      Free pages backing preloaded data (e.g., kernel modules) to the
    *      system.  Currently only supported on platforms that create a
    *      vm_phys segment for preloaded data.
    */
   void
   kmem_bootstrap_free(vm_offset_t start, vm_size_t size)
   {
   #if defined(__i386__) || defined(__amd64__)
           struct vm_domain *vmd;
           vm_offset_t end, va;
           vm_paddr_t pa;
           vm_page_t m;
   
           end = trunc_page(start + size);
           start = round_page(start);
   
   #ifdef __amd64__
           /*
            * Preloaded files do not have execute permissions by default on amd64.
            * Restore the default permissions to ensure that the direct map alias
            * is updated.
            */
           pmap_change_prot(start, end - start, VM_PROT_RW);
   #endif
           for (va = start; va < end; va += PAGE_SIZE) {
                   pa = pmap_kextract(va);
                   m = PHYS_TO_VM_PAGE(pa);
   
                   vmd = vm_pagequeue_domain(m);
                   vm_domain_free_lock(vmd);
                   vm_phys_free_pages(m, 0);
                   vm_domain_free_unlock(vmd);
   
                   vm_domain_freecnt_inc(vmd, 1);
                   vm_cnt.v_page_count++;
           }
           pmap_remove(kernel_pmap, start, end);
           (void)vmem_add(kernel_arena, start, end - start, M_WAITOK);
   #endif
   }
   
   /*
    * Allow userspace to directly trigger the VM drain routine for testing
    * purposes.
    */
   static int
   debug_vm_lowmem(SYSCTL_HANDLER_ARGS)
   {
           int error, i;
   
           i = 0;
           error = sysctl_handle_int(oidp, &i, 0, req);
           if (error)
                   return (error);
           if ((i & ~(VM_LOW_KMEM | VM_LOW_PAGES)) != 0)
                   return (EINVAL);
           if (i != 0)
                   EVENTHANDLER_INVOKE(vm_lowmem, i);
           return (0);
   }
   
   SYSCTL_PROC(_debug, OID_AUTO, vm_lowmem, CTLTYPE_INT | CTLFLAG_MPSAFE | CTLFLAG_RW, 0, 0,
       debug_vm_lowmem, "I", "set to trigger vm_lowmem event with given flags");

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