/*      $NetBSD: uvm_anon.c,v 1.80 2020/10/25 00:05:26 chs Exp $        */

/*
* Copyright (c) 1997 Charles D. Cranor and Washington University.
* All rights reserved.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/

/*
* uvm_anon.c: uvm anon ops
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_anon.c,v 1.80 2020/10/25 00:05:26 chs Exp $");

#include "opt_uvmhist.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/pool.h>
#include <sys/kernel.h>
#include <sys/atomic.h>

#include <uvm/uvm.h>
#include <uvm/uvm_swap.h>
#include <uvm/uvm_pdpolicy.h>

static struct pool_cache        uvm_anon_cache;

static int                      uvm_anon_ctor(void *, void *, int);

void
uvm_anon_init(void)
{

       pool_cache_bootstrap(&uvm_anon_cache, sizeof(struct vm_anon), 0, 0,
           PR_LARGECACHE, "anonpl", NULL, IPL_NONE, uvm_anon_ctor,
           NULL, NULL);
}

static int
uvm_anon_ctor(void *arg, void *object, int flags)
{
       struct vm_anon *anon = object;

       anon->an_ref = 0;
       anon->an_lock = NULL;
       anon->an_page = NULL;
#if defined(VMSWAP)
       anon->an_swslot = 0;
#endif
       return 0;
}

/*
* uvm_analloc: allocate a new anon.
*
* => anon will have no lock associated.
*/
struct vm_anon *
uvm_analloc(void)
{
       struct vm_anon *anon;

       anon = pool_cache_get(&uvm_anon_cache, PR_NOWAIT);
       if (anon) {
               KASSERT(anon->an_ref == 0);
               KASSERT(anon->an_lock == NULL);
               KASSERT(anon->an_page == NULL);
#if defined(VMSWAP)
               KASSERT(anon->an_swslot == 0);
#endif
               anon->an_ref = 1;
       }
       return anon;
}

/*
* uvm_anfree: free a single anon structure
*
* => anon must be removed from the amap (if anon was in an amap).
* => amap must be locked, if anon was owned by amap.
* => we may drop and re-acquire the lock here (to break loans).
*/
void
uvm_anfree(struct vm_anon *anon)
{
       struct vm_page *pg = anon->an_page, *pg2 __diagused;

       UVMHIST_FUNC(__func__);
       UVMHIST_CALLARGS(maphist,"(anon=%#jx)", (uintptr_t)anon, 0,0,0);

       KASSERT(anon->an_lock == NULL || rw_write_held(anon->an_lock));
       KASSERT(anon->an_ref == 0);

       /*
        * Dispose of the page, if it is resident.
        */

       if (__predict_true(pg != NULL)) {
               KASSERT(anon->an_lock != NULL);

               /*
                * If there is a resident page and it is loaned, then anon
                * may not own it.  Call out to uvm_anon_lockloanpg() to
                * identify and lock the real owner of the page.
                */

               if (__predict_false(pg->loan_count != 0)) {
                       pg2 = uvm_anon_lockloanpg(anon);
                       KASSERT(pg2 == pg);
               }

               /*
                * If the page is owned by a UVM object (now locked),
                * then kill the loan on the page rather than free it,
                * and release the object lock.
                */

               if (__predict_false(pg->uobject != NULL)) {
                       mutex_enter(&pg->interlock);
                       KASSERT(pg->loan_count > 0);
                       pg->loan_count--;
                       pg->uanon = NULL;
                       mutex_exit(&pg->interlock);
                       rw_exit(pg->uobject->vmobjlock);
               } else {

                       /*
                        * If page has no UVM object, then anon is the owner,
                        * and it is already locked.
                        */

                       KASSERT((pg->flags & PG_RELEASED) == 0);
                       pmap_page_protect(pg, VM_PROT_NONE);

                       /*
                        * If the page is busy, mark it as PG_RELEASED, so
                        * that uvm_anon_release(9) would release it later.
                        */

                       if (__predict_false((pg->flags & PG_BUSY) != 0)) {
                               pg->flags |= PG_RELEASED;
                               rw_obj_hold(anon->an_lock);
                               return;
                       }
                       uvm_pagefree(pg);
                       UVMHIST_LOG(maphist, "anon %#jx, page %#jx: "
                           "freed now!", (uintptr_t)anon, (uintptr_t)pg,
                           0, 0);
               }
       } else {
#if defined(VMSWAP)
               if (anon->an_swslot > 0) {
                       /* This page is no longer only in swap. */
                       KASSERT(uvmexp.swpgonly > 0);
                       atomic_dec_uint(&uvmexp.swpgonly);
               }
#endif
       }
       anon->an_lock = NULL;

       /*
        * Free any swap resources, leave a page replacement hint.
        */

       uvm_anon_dropswap(anon);
       uvmpdpol_anfree(anon);
       UVMHIST_LOG(maphist,"<- done!",0,0,0,0);
       pool_cache_put(&uvm_anon_cache, anon);
}

/*
* uvm_anon_lockloanpg: given a locked anon, lock its resident page owner.
*
* => anon is locked by caller
* => on return: anon is locked
*               if there is a resident page:
*                      if it has a uobject, it is locked by us
*                      if it is ownerless, we take over as owner
*               we return the resident page (it can change during
*               this function)
* => note that the only time an anon has an ownerless resident page
*      is if the page was loaned from a uvm_object and the uvm_object
*      disowned it
* => this only needs to be called when you want to do an operation
*      on an anon's resident page and that page has a non-zero loan
*      count.
*/
struct vm_page *
uvm_anon_lockloanpg(struct vm_anon *anon)
{
       struct vm_page *pg;
       krw_t op;

       KASSERT(rw_lock_held(anon->an_lock));

       /*
        * loop while we have a resident page that has a non-zero loan count.
        * if we successfully get our lock, we will "break" the loop.
        * note that the test for pg->loan_count is not protected -- this
        * may produce false positive results.   note that a false positive
        * result may cause us to do more work than we need to, but it will
        * not produce an incorrect result.
        */

       while (((pg = anon->an_page) != NULL) && pg->loan_count != 0) {
               mutex_enter(&pg->interlock);
               if (pg->uobject) {
                       /*
                        * if we didn't get a lock (try lock failed), then we
                        * toggle our anon lock and try again
                        */

                       if (!rw_tryenter(pg->uobject->vmobjlock, RW_WRITER)) {
                               /*
                                * someone locking the object has a chance to
                                * lock us right now
                                *
                                * XXX Better than yielding but inadequate.
                                */
                               mutex_exit(&pg->interlock);
                               op = rw_lock_op(anon->an_lock);
                               rw_exit(anon->an_lock);
                               kpause("lkloanpg", false, 1, NULL);
                               rw_enter(anon->an_lock, op);
                               continue;
                       }
               }

               /*
                * If page is un-owned i.e. the object dropped its ownership,
                * then we have to take the ownership.
                */

               if (pg->uobject == NULL && (pg->flags & PG_ANON) == 0) {
                       pg->flags |= PG_ANON;
                       pg->loan_count--;
               }
               mutex_exit(&pg->interlock);
               break;
       }
       return pg;
}

#if defined(VMSWAP)

/*
* uvm_anon_pagein: fetch an anon's page.
*
* => anon must be locked, and is unlocked upon return.
* => returns true if pagein was aborted due to lack of memory.
*/

bool
uvm_anon_pagein(struct vm_amap *amap, struct vm_anon *anon)
{
       struct vm_page *pg;
       struct uvm_object *uobj;

       KASSERT(rw_write_held(anon->an_lock));
       KASSERT(anon->an_lock == amap->am_lock);

       /*
        * Get the page of the anon.
        */

       switch (uvmfault_anonget(NULL, amap, anon)) {
       case 0:
               /* Success - we have the page. */
               KASSERT(rw_write_held(anon->an_lock));
               break;
       case EIO:
       case ERESTART:
               /*
                * Nothing more to do on errors.  ERESTART means that the
                * anon was freed.
                */
               return false;
       case ENOLCK:
               panic("uvm_anon_pagein");
       default:
               return true;
       }

       /*
        * Mark the page as dirty and clear its swslot.
        */

       pg = anon->an_page;
       uobj = pg->uobject;
       if (anon->an_swslot > 0) {
               uvm_swap_free(anon->an_swslot, 1);
       }
       anon->an_swslot = 0;
       uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_DIRTY);

       /*
        * Deactivate the page (to put it on a page queue).
        */

       uvm_pagelock(pg);
       uvm_pagedeactivate(pg);
       uvm_pageunlock(pg);
       rw_exit(anon->an_lock);
       if (uobj) {
               rw_exit(uobj->vmobjlock);
       }
       return false;
}

/*
* uvm_anon_dropswap: release any swap resources from this anon.
*
* => anon must be locked or have a reference count of 0.
*/
void
uvm_anon_dropswap(struct vm_anon *anon)
{
       UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

       if (anon->an_swslot == 0)
               return;

       UVMHIST_LOG(maphist,"freeing swap for anon %#jx, paged to swslot %#jx",
                   (uintptr_t)anon, anon->an_swslot, 0, 0);
       uvm_swap_free(anon->an_swslot, 1);
       anon->an_swslot = 0;
}

#endif

/*
* uvm_anon_release: release an anon and its page.
*
* => anon should not have any references.
* => anon must be locked.
*/

void
uvm_anon_release(struct vm_anon *anon)
{
       struct vm_page *pg = anon->an_page;
       krwlock_t *lock;

       KASSERT(rw_write_held(anon->an_lock));
       KASSERT(pg != NULL);
       KASSERT((pg->flags & PG_RELEASED) != 0);
       KASSERT((pg->flags & PG_BUSY) != 0);
       KASSERT(pg->uobject == NULL);
       KASSERT(pg->uanon == anon);
       KASSERT(pg->loan_count == 0);
       KASSERT(anon->an_ref == 0);

       if ((pg->flags & PG_PAGEOUT) != 0) {
               pg->flags &= ~PG_PAGEOUT;
               uvm_pageout_done(1);
       }

       uvm_pagefree(pg);
       KASSERT(anon->an_page == NULL);
       lock = anon->an_lock;
       uvm_anfree(anon);
       rw_exit(lock);
       /* Note: extra reference is held for PG_RELEASED case. */
       rw_obj_free(lock);
}

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