/*      $NetBSD: uvm_page_status.c,v 1.6 2020/08/14 09:06:15 chs Exp $  */

/*-
* Copyright (c)2011 YAMAMOTO Takashi,
* 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 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 AUTHOR 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.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_page_status.c,v 1.6 2020/08/14 09:06:15 chs Exp $");

#include <sys/param.h>
#include <sys/systm.h>

#include <uvm/uvm.h>

/*
* page dirtiness status tracking
*
* separated from uvm_page.c mainly for rump
*/

/*
* these constants are chosen to match so that we can convert between
* them quickly.
*/

__CTASSERT(UVM_PAGE_STATUS_UNKNOWN == 0);
__CTASSERT(UVM_PAGE_STATUS_DIRTY == PG_DIRTY);
__CTASSERT(UVM_PAGE_STATUS_CLEAN == PG_CLEAN);

/*
* uvm_pagegetdirty: return the dirtiness status (one of UVM_PAGE_STATUS_
* values) of the page.
*
* called with the owner locked.
*/

unsigned int
uvm_pagegetdirty(struct vm_page *pg)
{
       struct uvm_object * const uobj __diagused = pg->uobject;

       KASSERT((~pg->flags & (PG_CLEAN|PG_DIRTY)) != 0);
       KASSERT(uvm_page_owner_locked_p(pg, false));
       KASSERT(uobj == NULL || ((pg->flags & PG_CLEAN) == 0) ==
               uvm_obj_page_dirty_p(pg));
       return pg->flags & (PG_CLEAN|PG_DIRTY);
}

/*
* uvm_pagemarkdirty: set the dirtiness status (one of UVM_PAGE_STATUS_ values)
* of the page.
*
* called with the owner locked.
*
* update the radix tree tag for object-owned page.
*
* if new status is UVM_PAGE_STATUS_UNKNOWN, clear pmap-level dirty bit
* so that later uvm_pagecheckdirty() can notice modifications on the page.
*/

void
uvm_pagemarkdirty(struct vm_page *pg, unsigned int newstatus)
{
       struct uvm_object * const uobj = pg->uobject;
       const unsigned int oldstatus = uvm_pagegetdirty(pg);
       enum cpu_count base;

       KASSERT((~newstatus & (PG_CLEAN|PG_DIRTY)) != 0);
       KASSERT((newstatus & ~(PG_CLEAN|PG_DIRTY)) == 0);
       KASSERT(uvm_page_owner_locked_p(pg, true));
       KASSERT(uobj == NULL || ((pg->flags & PG_CLEAN) == 0) ==
               uvm_obj_page_dirty_p(pg));

       if (oldstatus == newstatus) {
               return;
       }

       /*
        * set UVM_PAGE_DIRTY_TAG tag unless known CLEAN so that putpages can
        * find possibly-dirty pages quickly.
        */

       if (uobj != NULL) {
               if (newstatus == UVM_PAGE_STATUS_CLEAN) {
                       uvm_obj_page_clear_dirty(pg);
               } else if (oldstatus == UVM_PAGE_STATUS_CLEAN) {
                       /*
                        * on first dirty page, mark the object dirty.
                        * for vnodes this inserts to the syncer worklist.
                        */
                       if (uvm_obj_clean_p(uobj) &&
                           uobj->pgops->pgo_markdirty != NULL) {
                               (*uobj->pgops->pgo_markdirty)(uobj);
                       }
                       uvm_obj_page_set_dirty(pg);
               }
       }
       if (newstatus == UVM_PAGE_STATUS_UNKNOWN) {
               /*
                * start relying on pmap-level dirtiness tracking.
                */
               pmap_clear_modify(pg);
       }
       pg->flags &= ~(PG_CLEAN|PG_DIRTY);
       pg->flags |= newstatus;
       KASSERT(uobj == NULL || ((pg->flags & PG_CLEAN) == 0) ==
               uvm_obj_page_dirty_p(pg));
       if ((pg->flags & PG_STAT) != 0) {
               if ((pg->flags & PG_SWAPBACKED) != 0) {
                       base = CPU_COUNT_ANONUNKNOWN;
               } else {
                       base = CPU_COUNT_FILEUNKNOWN;
               }
               kpreempt_disable();
               CPU_COUNT(base + oldstatus, -1);
               CPU_COUNT(base + newstatus, +1);
               kpreempt_enable();
       }
}

/*
* uvm_pagecheckdirty: check if page is dirty, and remove its dirty bit.
*
* called with the owner locked.
*
* returns if the page was dirty.
*
* if protected is true, mark the page CLEAN.  otherwise, mark the page UNKNOWN.
* ("mark" in the sense of uvm_pagemarkdirty().)
*/

bool
uvm_pagecheckdirty(struct vm_page *pg, bool pgprotected)
{
       const unsigned int oldstatus = uvm_pagegetdirty(pg);
       bool modified;

       KASSERT(uvm_page_owner_locked_p(pg, true));

       /*
        * if pgprotected is true, mark the page CLEAN.
        * otherwise mark the page UNKNOWN unless it's CLEAN.
        *
        * possible transitions:
        *
        *      CLEAN   -> CLEAN  , modified = false
        *      UNKNOWN -> UNKNOWN, modified = true
        *      UNKNOWN -> UNKNOWN, modified = false
        *      UNKNOWN -> CLEAN  , modified = true
        *      UNKNOWN -> CLEAN  , modified = false
        *      DIRTY   -> UNKNOWN, modified = true
        *      DIRTY   -> CLEAN  , modified = true
        *
        * pmap_clear_modify is necessary if either of
        * oldstatus or newstatus is UVM_PAGE_STATUS_UNKNOWN.
        */

       if (oldstatus == UVM_PAGE_STATUS_CLEAN) {
               modified = false;
       } else {
               const unsigned int newstatus = pgprotected ?
                   UVM_PAGE_STATUS_CLEAN : UVM_PAGE_STATUS_UNKNOWN;

               if (oldstatus == UVM_PAGE_STATUS_DIRTY) {
                       modified = true;
                       if (newstatus == UVM_PAGE_STATUS_UNKNOWN) {
                               pmap_clear_modify(pg);
                       }
               } else {
                       KASSERT(oldstatus == UVM_PAGE_STATUS_UNKNOWN);
                       modified = pmap_clear_modify(pg);
               }
               uvm_pagemarkdirty(pg, newstatus);
       }
       return modified;
}

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