The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/uvm/uvm_loan.c

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    1 /*      $NetBSD: uvm_loan.c,v 1.52 2004/11/23 04:51:56 yamt Exp $       */
    2 
    3 /*
    4  *
    5  * Copyright (c) 1997 Charles D. Cranor and Washington University.
    6  * All rights reserved.
    7  *
    8  * Redistribution and use in source and binary forms, with or without
    9  * modification, are permitted provided that the following conditions
   10  * are met:
   11  * 1. Redistributions of source code must retain the above copyright
   12  *    notice, this list of conditions and the following disclaimer.
   13  * 2. Redistributions in binary form must reproduce the above copyright
   14  *    notice, this list of conditions and the following disclaimer in the
   15  *    documentation and/or other materials provided with the distribution.
   16  * 3. All advertising materials mentioning features or use of this software
   17  *    must display the following acknowledgement:
   18  *      This product includes software developed by Charles D. Cranor and
   19  *      Washington University.
   20  * 4. The name of the author may not be used to endorse or promote products
   21  *    derived from this software without specific prior written permission.
   22  *
   23  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   24  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   25  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   26  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   27  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   28  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   29  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   30  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   31  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   32  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   33  *
   34  * from: Id: uvm_loan.c,v 1.1.6.4 1998/02/06 05:08:43 chs Exp
   35  */
   36 
   37 /*
   38  * uvm_loan.c: page loanout handler
   39  */
   40 
   41 #include <sys/cdefs.h>
   42 __KERNEL_RCSID(0, "$NetBSD: uvm_loan.c,v 1.52 2004/11/23 04:51:56 yamt Exp $");
   43 
   44 #include <sys/param.h>
   45 #include <sys/systm.h>
   46 #include <sys/kernel.h>
   47 #include <sys/proc.h>
   48 #include <sys/malloc.h>
   49 #include <sys/mman.h>
   50 
   51 #include <uvm/uvm.h>
   52 
   53 /*
   54  * "loaned" pages are pages which are (read-only, copy-on-write) loaned
   55  * from the VM system to other parts of the kernel.   this allows page
   56  * copying to be avoided (e.g. you can loan pages from objs/anons to
   57  * the mbuf system).
   58  *
   59  * there are 3 types of loans possible:
   60  *  O->K  uvm_object page to wired kernel page (e.g. mbuf data area)
   61  *  A->K  anon page to wired kernel page (e.g. mbuf data area)
   62  *  O->A  uvm_object to anon loan (e.g. vnode page to an anon)
   63  * note that it possible to have an O page loaned to both an A and K
   64  * at the same time.
   65  *
   66  * loans are tracked by pg->loan_count.  an O->A page will have both
   67  * a uvm_object and a vm_anon, but PQ_ANON will not be set.   this sort
   68  * of page is considered "owned" by the uvm_object (not the anon).
   69  *
   70  * each loan of a page to the kernel bumps the pg->wire_count.  the
   71  * kernel mappings for these pages will be read-only and wired.  since
   72  * the page will also be wired, it will not be a candidate for pageout,
   73  * and thus will never be pmap_page_protect()'d with VM_PROT_NONE.  a
   74  * write fault in the kernel to one of these pages will not cause
   75  * copy-on-write.  instead, the page fault is considered fatal.  this
   76  * is because the kernel mapping will have no way to look up the
   77  * object/anon which the page is owned by.  this is a good side-effect,
   78  * since a kernel write to a loaned page is an error.
   79  *
   80  * owners that want to free their pages and discover that they are
   81  * loaned out simply "disown" them (the page becomes an orphan).  these
   82  * pages should be freed when the last loan is dropped.   in some cases
   83  * an anon may "adopt" an orphaned page.
   84  *
   85  * locking: to read pg->loan_count either the owner or the page queues
   86  * must be locked.   to modify pg->loan_count, both the owner of the page
   87  * and the PQs must be locked.   pg->flags is (as always) locked by
   88  * the owner of the page.
   89  *
   90  * note that locking from the "loaned" side is tricky since the object
   91  * getting the loaned page has no reference to the page's owner and thus
   92  * the owner could "die" at any time.   in order to prevent the owner
   93  * from dying the page queues should be locked.   this forces us to sometimes
   94  * use "try" locking.
   95  *
   96  * loans are typically broken by the following events:
   97  *  1. user-level xwrite fault to a loaned page
   98  *  2. pageout of clean+inactive O->A loaned page
   99  *  3. owner frees page (e.g. pager flush)
  100  *
  101  * note that loaning a page causes all mappings of the page to become
  102  * read-only (via pmap_page_protect).   this could have an unexpected
  103  * effect on normal "wired" pages if one is not careful (XXX).
  104  */
  105 
  106 /*
  107  * local prototypes
  108  */
  109 
  110 static int      uvm_loananon(struct uvm_faultinfo *, void ***,
  111                              int, struct vm_anon *);
  112 static int      uvm_loanentry(struct uvm_faultinfo *, void ***, int);
  113 static int      uvm_loanuobj(struct uvm_faultinfo *, void ***,
  114                              int, vaddr_t);
  115 static int      uvm_loanzero(struct uvm_faultinfo *, void ***, int);
  116 static void     uvm_unloananon(struct vm_anon **, int);
  117 static void     uvm_unloanpage(struct vm_page **, int);
  118 static int      uvm_loanpage(struct vm_page **, int);
  119 
  120 
  121 /*
  122  * inlines
  123  */
  124 
  125 /*
  126  * uvm_loanentry: loan out pages in a map entry (helper fn for uvm_loan())
  127  *
  128  * => "ufi" is the result of a successful map lookup (meaning that
  129  *      on entry the map is locked by the caller)
  130  * => we may unlock and then relock the map if needed (for I/O)
  131  * => we put our output result in "output"
  132  * => we always return with the map unlocked
  133  * => possible return values:
  134  *      -1 == error, map is unlocked
  135  *       0 == map relock error (try again!), map is unlocked
  136  *      >0 == number of pages we loaned, map is unlocked
  137  */
  138 
  139 static __inline int
  140 uvm_loanentry(ufi, output, flags)
  141         struct uvm_faultinfo *ufi;
  142         void ***output;
  143         int flags;
  144 {
  145         vaddr_t curaddr = ufi->orig_rvaddr;
  146         vsize_t togo = ufi->size;
  147         struct vm_aref *aref = &ufi->entry->aref;
  148         struct uvm_object *uobj = ufi->entry->object.uvm_obj;
  149         struct vm_anon *anon;
  150         int rv, result = 0;
  151 
  152         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  153 
  154         /*
  155          * lock us the rest of the way down (we unlock before return)
  156          */
  157         if (aref->ar_amap)
  158                 amap_lock(aref->ar_amap);
  159         if (uobj)
  160                 simple_lock(&uobj->vmobjlock);
  161 
  162         /*
  163          * loop until done
  164          */
  165         while (togo) {
  166 
  167                 /*
  168                  * find the page we want.   check the anon layer first.
  169                  */
  170 
  171                 if (aref->ar_amap) {
  172                         anon = amap_lookup(aref, curaddr - ufi->entry->start);
  173                 } else {
  174                         anon = NULL;
  175                 }
  176 
  177                 /* locked: map, amap, uobj */
  178                 if (anon) {
  179                         rv = uvm_loananon(ufi, output, flags, anon);
  180                 } else if (uobj) {
  181                         rv = uvm_loanuobj(ufi, output, flags, curaddr);
  182                 } else if (UVM_ET_ISCOPYONWRITE(ufi->entry)) {
  183                         rv = uvm_loanzero(ufi, output, flags);
  184                 } else {
  185                         uvmfault_unlockall(ufi, aref->ar_amap, uobj, NULL);
  186                         rv = -1;
  187                 }
  188                 /* locked: if (rv > 0) => map, amap, uobj  [o.w. unlocked] */
  189                 LOCK_ASSERT(rv > 0 || aref->ar_amap == NULL ||
  190                     !simple_lock_held(&aref->ar_amap->am_l));
  191                 LOCK_ASSERT(rv > 0 || uobj == NULL ||
  192                     !simple_lock_held(&uobj->vmobjlock));
  193 
  194                 /* total failure */
  195                 if (rv < 0) {
  196                         UVMHIST_LOG(loanhist, "failure %d", rv, 0,0,0);
  197                         return (-1);
  198                 }
  199 
  200                 /* relock failed, need to do another lookup */
  201                 if (rv == 0) {
  202                         UVMHIST_LOG(loanhist, "relock failure %d", result
  203                             ,0,0,0);
  204                         return (result);
  205                 }
  206 
  207                 /*
  208                  * got it... advance to next page
  209                  */
  210 
  211                 result++;
  212                 togo -= PAGE_SIZE;
  213                 curaddr += PAGE_SIZE;
  214         }
  215 
  216         /*
  217          * unlock what we locked, unlock the maps and return
  218          */
  219 
  220         if (aref->ar_amap)
  221                 amap_unlock(aref->ar_amap);
  222         if (uobj)
  223                 simple_unlock(&uobj->vmobjlock);
  224         uvmfault_unlockmaps(ufi, FALSE);
  225         UVMHIST_LOG(loanhist, "done %d", result, 0,0,0);
  226         return (result);
  227 }
  228 
  229 /*
  230  * normal functions
  231  */
  232 
  233 /*
  234  * uvm_loan: loan pages in a map out to anons or to the kernel
  235  *
  236  * => map should be unlocked
  237  * => start and len should be multiples of PAGE_SIZE
  238  * => result is either an array of anon's or vm_pages (depending on flags)
  239  * => flag values: UVM_LOAN_TOANON - loan to anons
  240  *                 UVM_LOAN_TOPAGE - loan to wired kernel page
  241  *    one and only one of these flags must be set!
  242  * => returns 0 (success), or an appropriate error number
  243  */
  244 
  245 int
  246 uvm_loan(map, start, len, v, flags)
  247         struct vm_map *map;
  248         vaddr_t start;
  249         vsize_t len;
  250         void *v;
  251         int flags;
  252 {
  253         struct uvm_faultinfo ufi;
  254         void **result, **output;
  255         int rv, error;
  256 
  257         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  258 
  259         /*
  260          * ensure that one and only one of the flags is set
  261          */
  262 
  263         KASSERT(((flags & UVM_LOAN_TOANON) == 0) ^
  264                 ((flags & UVM_LOAN_TOPAGE) == 0));
  265         KASSERT((map->flags & VM_MAP_INTRSAFE) == 0);
  266 
  267         /*
  268          * "output" is a pointer to the current place to put the loaned page.
  269          */
  270 
  271         result = v;
  272         output = &result[0];    /* start at the beginning ... */
  273 
  274         /*
  275          * while we've got pages to do
  276          */
  277 
  278         while (len > 0) {
  279 
  280                 /*
  281                  * fill in params for a call to uvmfault_lookup
  282                  */
  283 
  284                 ufi.orig_map = map;
  285                 ufi.orig_rvaddr = start;
  286                 ufi.orig_size = len;
  287 
  288                 /*
  289                  * do the lookup, the only time this will fail is if we hit on
  290                  * an unmapped region (an error)
  291                  */
  292 
  293                 if (!uvmfault_lookup(&ufi, FALSE)) {
  294                         error = ENOENT;
  295                         goto fail;
  296                 }
  297 
  298                 /*
  299                  * map now locked.  now do the loanout...
  300                  */
  301 
  302                 rv = uvm_loanentry(&ufi, &output, flags);
  303                 if (rv < 0) {
  304                         /* all unlocked due to error */
  305                         error = EINVAL;
  306                         goto fail;
  307                 }
  308 
  309                 /*
  310                  * done!  the map is unlocked.  advance, if possible.
  311                  *
  312                  * XXXCDC: could be recoded to hold the map lock with
  313                  *         smarter code (but it only happens on map entry
  314                  *         boundaries, so it isn't that bad).
  315                  */
  316 
  317                 if (rv) {
  318                         rv <<= PAGE_SHIFT;
  319                         len -= rv;
  320                         start += rv;
  321                 }
  322         }
  323         UVMHIST_LOG(loanhist, "success", 0,0,0,0);
  324         return 0;
  325 
  326 fail:
  327         /*
  328          * failed to complete loans.  drop any loans and return failure code.
  329          * map is already unlocked.
  330          */
  331 
  332         if (output - result) {
  333                 if (flags & UVM_LOAN_TOANON) {
  334                         uvm_unloananon((struct vm_anon **)result,
  335                             output - result);
  336                 } else {
  337                         uvm_unloanpage((struct vm_page **)result,
  338                             output - result);
  339                 }
  340         }
  341         UVMHIST_LOG(loanhist, "error %d", error,0,0,0);
  342         return (error);
  343 }
  344 
  345 /*
  346  * uvm_loananon: loan a page from an anon out
  347  *
  348  * => called with map, amap, uobj locked
  349  * => return value:
  350  *      -1 = fatal error, everything is unlocked, abort.
  351  *       0 = lookup in ufi went stale, everything unlocked, relookup and
  352  *              try again
  353  *       1 = got it, everything still locked
  354  */
  355 
  356 int
  357 uvm_loananon(ufi, output, flags, anon)
  358         struct uvm_faultinfo *ufi;
  359         void ***output;
  360         int flags;
  361         struct vm_anon *anon;
  362 {
  363         struct vm_page *pg;
  364         int error;
  365 
  366         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  367 
  368         /*
  369          * if we are loaning to "another" anon then it is easy, we just
  370          * bump the reference count on the current anon and return a
  371          * pointer to it (it becomes copy-on-write shared).
  372          */
  373 
  374         if (flags & UVM_LOAN_TOANON) {
  375                 simple_lock(&anon->an_lock);
  376                 pg = anon->u.an_page;
  377                 if (pg && (pg->pqflags & PQ_ANON) != 0 && anon->an_ref == 1) {
  378                         if (pg->wire_count > 0) {
  379                                 UVMHIST_LOG(loanhist, "->A wired %p", pg,0,0,0);
  380                                 uvmfault_unlockall(ufi,
  381                                     ufi->entry->aref.ar_amap,
  382                                     ufi->entry->object.uvm_obj, anon);
  383                                 return (-1);
  384                         }
  385                         pmap_page_protect(pg, VM_PROT_READ);
  386                 }
  387                 anon->an_ref++;
  388                 **output = anon;
  389                 (*output)++;
  390                 simple_unlock(&anon->an_lock);
  391                 UVMHIST_LOG(loanhist, "->A done", 0,0,0,0);
  392                 return (1);
  393         }
  394 
  395         /*
  396          * we are loaning to a kernel-page.   we need to get the page
  397          * resident so we can wire it.   uvmfault_anonget will handle
  398          * this for us.
  399          */
  400 
  401         simple_lock(&anon->an_lock);
  402         error = uvmfault_anonget(ufi, ufi->entry->aref.ar_amap, anon);
  403 
  404         /*
  405          * if we were unable to get the anon, then uvmfault_anonget has
  406          * unlocked everything and returned an error code.
  407          */
  408 
  409         if (error) {
  410                 UVMHIST_LOG(loanhist, "error %d", error,0,0,0);
  411 
  412                 /* need to refault (i.e. refresh our lookup) ? */
  413                 if (error == ERESTART) {
  414                         return (0);
  415                 }
  416 
  417                 /* "try again"?   sleep a bit and retry ... */
  418                 if (error == EAGAIN) {
  419                         tsleep(&lbolt, PVM, "loanagain", 0);
  420                         return (0);
  421                 }
  422 
  423                 /* otherwise flag it as an error */
  424                 return (-1);
  425         }
  426 
  427         /*
  428          * we have the page and its owner locked: do the loan now.
  429          */
  430 
  431         pg = anon->u.an_page;
  432         uvm_lock_pageq();
  433         if (pg->wire_count > 0) {
  434                 uvm_unlock_pageq();
  435                 UVMHIST_LOG(loanhist, "->K wired %p", pg,0,0,0);
  436                 KASSERT(pg->uobject == NULL);
  437                 uvmfault_unlockall(ufi, ufi->entry->aref.ar_amap,
  438                     ufi->entry->object.uvm_obj, anon);
  439                 return (-1);
  440         }
  441         if (pg->loan_count == 0) {
  442                 pmap_page_protect(pg, VM_PROT_READ);
  443         }
  444         pg->loan_count++;
  445         uvm_pagedequeue(pg);
  446         uvm_unlock_pageq();
  447         **output = pg;
  448         (*output)++;
  449 
  450         /* unlock anon and return success */
  451         if (pg->uobject)        /* XXXCDC: what if this is our uobj? bad */
  452                 simple_unlock(&pg->uobject->vmobjlock);
  453         simple_unlock(&anon->an_lock);
  454         UVMHIST_LOG(loanhist, "->K done", 0,0,0,0);
  455         return (1);
  456 }
  457 
  458 /*
  459  * uvm_loanpage: loan out pages to kernel (->K)
  460  *
  461  * => pages should be object-owned and the object should be locked.
  462  * => in the case of error, the object might be unlocked and relocked.
  463  * => caller should busy the pages beforehand.
  464  * => pages will be unbusied.
  465  * => fail with EBUSY if meet a wired page.
  466  */
  467 static int
  468 uvm_loanpage(pgpp, npages)
  469         struct vm_page **pgpp;
  470         int npages;
  471 {
  472         int i;
  473         int error = 0;
  474 
  475         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  476 
  477         for (i = 0; i < npages; i++) {
  478                 struct vm_page *pg = pgpp[i];
  479 
  480                 KASSERT(pg->uobject != NULL);
  481                 KASSERT(pg->uobject == pgpp[0]->uobject);
  482                 KASSERT(!(pg->flags & (PG_RELEASED|PG_PAGEOUT)));
  483                 LOCK_ASSERT(simple_lock_held(&pg->uobject->vmobjlock));
  484                 KASSERT(pg->flags & PG_BUSY);
  485 
  486                 uvm_lock_pageq();
  487                 if (pg->wire_count > 0) {
  488                         uvm_unlock_pageq();
  489                         UVMHIST_LOG(loanhist, "wired %p", pg,0,0,0);
  490                         error = EBUSY;
  491                         break;
  492                 }
  493                 if (pg->loan_count == 0) {
  494                         pmap_page_protect(pg, VM_PROT_READ);
  495                 }
  496                 pg->loan_count++;
  497                 uvm_pagedequeue(pg);
  498                 uvm_unlock_pageq();
  499         }
  500 
  501         uvm_page_unbusy(pgpp, npages);
  502 
  503         if (error) {
  504                 /*
  505                  * backout what we've done
  506                  */
  507                 struct simplelock *slock = &pgpp[0]->uobject->vmobjlock;
  508 
  509                 simple_unlock(slock);
  510                 uvm_unloan(pgpp, i, UVM_LOAN_TOPAGE);
  511                 simple_lock(slock);
  512         }
  513 
  514         UVMHIST_LOG(loanhist, "done %d", error,0,0,0);
  515         return error;
  516 }
  517 
  518 /*
  519  * XXX UBC temp limit
  520  * number of pages to get at once.
  521  * should be <= MAX_READ_AHEAD in genfs_vnops.c
  522  */
  523 #define UVM_LOAN_GET_CHUNK      16
  524 
  525 /*
  526  * uvm_loanuobjpages: loan pages from a uobj out (O->K)
  527  *
  528  * => uobj shouldn't be locked.  (we'll lock it)
  529  * => fail with EBUSY if we meet a wired page.
  530  */
  531 int
  532 uvm_loanuobjpages(uobj, pgoff, orignpages, origpgpp)
  533         struct uvm_object *uobj;
  534         voff_t pgoff;
  535         int orignpages;
  536         struct vm_page **origpgpp;
  537 {
  538         int ndone; /* # of pages loaned out */
  539         struct vm_page **pgpp;
  540         int error;
  541         int i;
  542         struct simplelock *slock;
  543 
  544         pgpp = origpgpp;
  545         for (ndone = 0; ndone < orignpages; ) {
  546                 int npages;
  547                 /* npendloan: # of pages busied but not loand out yet. */
  548                 int npendloan = 0xdead; /* XXX gcc */
  549 reget:
  550                 npages = MIN(UVM_LOAN_GET_CHUNK, orignpages - ndone);
  551                 simple_lock(&uobj->vmobjlock);
  552                 error = (*uobj->pgops->pgo_get)(uobj,
  553                     pgoff + (ndone << PAGE_SHIFT), pgpp, &npages, 0,
  554                     VM_PROT_READ, 0, PGO_SYNCIO);
  555                 if (error == EAGAIN) {
  556                         tsleep(&lbolt, PVM, "nfsread", 0);
  557                         continue;
  558                 }
  559                 if (error)
  560                         goto fail;
  561 
  562                 KASSERT(npages > 0);
  563 
  564                 /* loan and unbusy pages */
  565                 slock = NULL;
  566                 for (i = 0; i < npages; i++) {
  567                         struct simplelock *nextslock; /* slock for next page */
  568                         struct vm_page *pg = *pgpp;
  569 
  570                         /* XXX assuming that the page is owned by uobj */
  571                         KASSERT(pg->uobject != NULL);
  572                         nextslock = &pg->uobject->vmobjlock;
  573 
  574                         if (slock != nextslock) {
  575                                 if (slock) {
  576                                         KASSERT(npendloan > 0);
  577                                         error = uvm_loanpage(pgpp - npendloan,
  578                                             npendloan);
  579                                         simple_unlock(slock);
  580                                         if (error)
  581                                                 goto fail;
  582                                         ndone += npendloan;
  583                                         KASSERT(origpgpp + ndone == pgpp);
  584                                 }
  585                                 slock = nextslock;
  586                                 npendloan = 0;
  587                                 simple_lock(slock);
  588                         }
  589 
  590                         if ((pg->flags & PG_RELEASED) != 0) {
  591                                 /*
  592                                  * release pages and try again.
  593                                  */
  594                                 simple_unlock(slock);
  595                                 for (; i < npages; i++) {
  596                                         pg = pgpp[i];
  597                                         slock = &pg->uobject->vmobjlock;
  598 
  599                                         simple_lock(slock);
  600                                         uvm_lock_pageq();
  601                                         uvm_page_unbusy(&pg, 1);
  602                                         uvm_unlock_pageq();
  603                                         simple_unlock(slock);
  604                                 }
  605                                 goto reget;
  606                         }
  607 
  608                         npendloan++;
  609                         pgpp++;
  610                         KASSERT(origpgpp + ndone + npendloan == pgpp);
  611                 }
  612                 KASSERT(slock != NULL);
  613                 KASSERT(npendloan > 0);
  614                 error = uvm_loanpage(pgpp - npendloan, npendloan);
  615                 simple_unlock(slock);
  616                 if (error)
  617                         goto fail;
  618                 ndone += npendloan;
  619                 KASSERT(origpgpp + ndone == pgpp);
  620         }
  621 
  622         return 0;
  623 
  624 fail:
  625         uvm_unloan(origpgpp, ndone, UVM_LOAN_TOPAGE);
  626 
  627         return error;
  628 }
  629 
  630 /*
  631  * uvm_loanuobj: loan a page from a uobj out
  632  *
  633  * => called with map, amap, uobj locked
  634  * => return value:
  635  *      -1 = fatal error, everything is unlocked, abort.
  636  *       0 = lookup in ufi went stale, everything unlocked, relookup and
  637  *              try again
  638  *       1 = got it, everything still locked
  639  */
  640 
  641 static int
  642 uvm_loanuobj(ufi, output, flags, va)
  643         struct uvm_faultinfo *ufi;
  644         void ***output;
  645         int flags;
  646         vaddr_t va;
  647 {
  648         struct vm_amap *amap = ufi->entry->aref.ar_amap;
  649         struct uvm_object *uobj = ufi->entry->object.uvm_obj;
  650         struct vm_page *pg;
  651         struct vm_anon *anon;
  652         int error, npages;
  653         boolean_t locked;
  654 
  655         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  656 
  657         /*
  658          * first we must make sure the page is resident.
  659          *
  660          * XXXCDC: duplicate code with uvm_fault().
  661          */
  662 
  663         if (uobj->pgops->pgo_get) {     /* try locked pgo_get */
  664                 npages = 1;
  665                 pg = NULL;
  666                 error = (*uobj->pgops->pgo_get)(uobj,
  667                     va - ufi->entry->start + ufi->entry->offset,
  668                     &pg, &npages, 0, VM_PROT_READ, MADV_NORMAL, PGO_LOCKED);
  669         } else {
  670                 error = EIO;            /* must have pgo_get op */
  671         }
  672 
  673         /*
  674          * check the result of the locked pgo_get.  if there is a problem,
  675          * then we fail the loan.
  676          */
  677 
  678         if (error && error != EBUSY) {
  679                 uvmfault_unlockall(ufi, amap, uobj, NULL);
  680                 return (-1);
  681         }
  682 
  683         /*
  684          * if we need to unlock for I/O, do so now.
  685          */
  686 
  687         if (error == EBUSY) {
  688                 uvmfault_unlockall(ufi, amap, NULL, NULL);
  689 
  690                 /* locked: uobj */
  691                 npages = 1;
  692                 error = (*uobj->pgops->pgo_get)(uobj,
  693                     va - ufi->entry->start + ufi->entry->offset,
  694                     &pg, &npages, 0, VM_PROT_READ, MADV_NORMAL, PGO_SYNCIO);
  695                 /* locked: <nothing> */
  696 
  697                 if (error) {
  698                         if (error == EAGAIN) {
  699                                 tsleep(&lbolt, PVM, "fltagain2", 0);
  700                                 return (0);
  701                         }
  702                         return (-1);
  703                 }
  704 
  705                 /*
  706                  * pgo_get was a success.   attempt to relock everything.
  707                  */
  708 
  709                 locked = uvmfault_relock(ufi);
  710                 if (locked && amap)
  711                         amap_lock(amap);
  712                 simple_lock(&uobj->vmobjlock);
  713 
  714                 /*
  715                  * verify that the page has not be released and re-verify
  716                  * that amap slot is still free.   if there is a problem we
  717                  * drop our lock (thus force a lookup refresh/retry).
  718                  */
  719 
  720                 if ((pg->flags & PG_RELEASED) != 0 ||
  721                     (locked && amap && amap_lookup(&ufi->entry->aref,
  722                     ufi->orig_rvaddr - ufi->entry->start))) {
  723                         if (locked)
  724                                 uvmfault_unlockall(ufi, amap, NULL, NULL);
  725                         locked = FALSE;
  726                 }
  727 
  728                 /*
  729                  * didn't get the lock?   release the page and retry.
  730                  */
  731 
  732                 if (locked == FALSE) {
  733                         if (pg->flags & PG_WANTED) {
  734                                 wakeup(pg);
  735                         }
  736                         if (pg->flags & PG_RELEASED) {
  737                                 uvm_lock_pageq();
  738                                 uvm_pagefree(pg);
  739                                 uvm_unlock_pageq();
  740                                 return (0);
  741                         }
  742                         uvm_lock_pageq();
  743                         uvm_pageactivate(pg);
  744                         uvm_unlock_pageq();
  745                         pg->flags &= ~(PG_BUSY|PG_WANTED);
  746                         UVM_PAGE_OWN(pg, NULL);
  747                         simple_unlock(&uobj->vmobjlock);
  748                         return (0);
  749                 }
  750         }
  751 
  752         /*
  753          * at this point we have the page we want ("pg") marked PG_BUSY for us
  754          * and we have all data structures locked.  do the loanout.  page can
  755          * not be PG_RELEASED (we caught this above).
  756          */
  757 
  758         if ((flags & UVM_LOAN_TOANON) == 0) {
  759                 if (uvm_loanpage(&pg, 1)) {
  760                         uvmfault_unlockall(ufi, amap, uobj, NULL);
  761                         return (-1);
  762                 }
  763                 **output = pg;
  764                 (*output)++;
  765                 return (1);
  766         }
  767 
  768         /*
  769          * must be a loan to an anon.   check to see if there is already
  770          * an anon associated with this page.  if so, then just return
  771          * a reference to this object.   the page should already be
  772          * mapped read-only because it is already on loan.
  773          */
  774 
  775         if (pg->uanon) {
  776                 anon = pg->uanon;
  777                 simple_lock(&anon->an_lock);
  778                 anon->an_ref++;
  779                 simple_unlock(&anon->an_lock);
  780                 if (pg->flags & PG_WANTED) {
  781                         wakeup(pg);
  782                 }
  783                 pg->flags &= ~(PG_WANTED|PG_BUSY);
  784                 UVM_PAGE_OWN(pg, NULL);
  785                 **output = anon;
  786                 (*output)++;
  787                 return (1);
  788         }
  789 
  790         /*
  791          * need to allocate a new anon
  792          */
  793 
  794         anon = uvm_analloc();
  795         if (anon == NULL) {
  796                 goto fail;
  797         }
  798         anon->u.an_page = pg;
  799         pg->uanon = anon;
  800         uvm_lock_pageq();
  801         if (pg->wire_count > 0) {
  802                 uvm_unlock_pageq();
  803                 UVMHIST_LOG(loanhist, "wired %p", pg,0,0,0);
  804                 pg->uanon = NULL;
  805                 anon->u.an_page = NULL;
  806                 anon->an_ref--;
  807                 simple_unlock(&anon->an_lock);
  808                 uvm_anfree(anon);
  809                 goto fail;
  810         }
  811         if (pg->loan_count == 0) {
  812                 pmap_page_protect(pg, VM_PROT_READ);
  813         }
  814         pg->loan_count++;
  815         uvm_pageactivate(pg);
  816         uvm_unlock_pageq();
  817         if (pg->flags & PG_WANTED) {
  818                 wakeup(pg);
  819         }
  820         pg->flags &= ~(PG_WANTED|PG_BUSY);
  821         UVM_PAGE_OWN(pg, NULL);
  822         simple_unlock(&anon->an_lock);
  823         **output = anon;
  824         (*output)++;
  825         return (1);
  826 
  827 fail:
  828         UVMHIST_LOG(loanhist, "fail", 0,0,0,0);
  829         /*
  830          * unlock everything and bail out.
  831          */
  832         if (pg->flags & PG_WANTED) {
  833                 wakeup(pg);
  834         }
  835         pg->flags &= ~(PG_WANTED|PG_BUSY);
  836         UVM_PAGE_OWN(pg, NULL);
  837         uvmfault_unlockall(ufi, amap, uobj, NULL);
  838         return (-1);
  839 }
  840 
  841 /*
  842  * uvm_loanzero: loan a zero-fill page out
  843  *
  844  * => called with map, amap, uobj locked
  845  * => return value:
  846  *      -1 = fatal error, everything is unlocked, abort.
  847  *       0 = lookup in ufi went stale, everything unlocked, relookup and
  848  *              try again
  849  *       1 = got it, everything still locked
  850  */
  851 
  852 static struct uvm_object uvm_loanzero_object;
  853 
  854 static int
  855 uvm_loanzero(ufi, output, flags)
  856         struct uvm_faultinfo *ufi;
  857         void ***output;
  858         int flags;
  859 {
  860         struct vm_anon *anon;
  861         struct vm_page *pg;
  862         struct uvm_object *uobj = ufi->entry->object.uvm_obj;
  863         struct vm_amap *amap = ufi->entry->aref.ar_amap;
  864 
  865         UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist);
  866 again:
  867         simple_lock(&uvm_loanzero_object.vmobjlock);
  868 
  869         /*
  870          * first, get ahold of our single zero page.
  871          */
  872 
  873         if (__predict_false((pg =
  874                              TAILQ_FIRST(&uvm_loanzero_object.memq)) == NULL)) {
  875                 while ((pg = uvm_pagealloc(&uvm_loanzero_object, 0, NULL,
  876                                            UVM_PGA_ZERO)) == NULL) {
  877                         simple_unlock(&uvm_loanzero_object.vmobjlock);
  878                         uvmfault_unlockall(ufi, amap, uobj, NULL);
  879                         uvm_wait("loanzero");
  880                         if (!uvmfault_relock(ufi)) {
  881                                 return (0);
  882                         }
  883                         if (amap) {
  884                                 amap_lock(amap);
  885                         }
  886                         if (uobj) {
  887                                 simple_lock(&uobj->vmobjlock);
  888                         }
  889                         goto again;
  890                 }
  891 
  892                 /* got a zero'd page. */
  893                 pg->flags &= ~(PG_WANTED|PG_BUSY|PG_FAKE);
  894                 pg->flags |= PG_RDONLY;
  895                 uvm_lock_pageq();
  896                 uvm_pageactivate(pg);
  897                 uvm_unlock_pageq();
  898                 UVM_PAGE_OWN(pg, NULL);
  899         }
  900 
  901         if ((flags & UVM_LOAN_TOANON) == 0) {   /* loaning to kernel-page */
  902                 uvm_lock_pageq();
  903                 pg->loan_count++;
  904                 uvm_pagedequeue(pg);
  905                 uvm_unlock_pageq();
  906                 simple_unlock(&uvm_loanzero_object.vmobjlock);
  907                 **output = pg;
  908                 (*output)++;
  909                 return (1);
  910         }
  911 
  912         /*
  913          * loaning to an anon.  check to see if there is already an anon
  914          * associated with this page.  if so, then just return a reference
  915          * to this object.
  916          */
  917 
  918         if (pg->uanon) {
  919                 anon = pg->uanon;
  920                 simple_lock(&anon->an_lock);
  921                 anon->an_ref++;
  922                 simple_unlock(&anon->an_lock);
  923                 simple_unlock(&uvm_loanzero_object.vmobjlock);
  924                 **output = anon;
  925                 (*output)++;
  926                 return (1);
  927         }
  928 
  929         /*
  930          * need to allocate a new anon
  931          */
  932 
  933         anon = uvm_analloc();
  934         if (anon == NULL) {
  935                 /* out of swap causes us to fail */
  936                 simple_unlock(&uvm_loanzero_object.vmobjlock);
  937                 uvmfault_unlockall(ufi, amap, uobj, NULL);
  938                 return (-1);
  939         }
  940         anon->u.an_page = pg;
  941         pg->uanon = anon;
  942         uvm_lock_pageq();
  943         pg->loan_count++;
  944         uvm_pageactivate(pg);
  945         uvm_unlock_pageq();
  946         simple_unlock(&uvm_loanzero_object.vmobjlock);
  947         **output = anon;
  948         (*output)++;
  949         return (1);
  950 }
  951 
  952 
  953 /*
  954  * uvm_unloananon: kill loans on anons (basically a normal ref drop)
  955  *
  956  * => we expect all our resources to be unlocked
  957  */
  958 
  959 static void
  960 uvm_unloananon(aloans, nanons)
  961         struct vm_anon **aloans;
  962         int nanons;
  963 {
  964         struct vm_anon *anon;
  965 
  966         while (nanons-- > 0) {
  967                 int refs;
  968 
  969                 anon = *aloans++;
  970                 simple_lock(&anon->an_lock);
  971                 refs = --anon->an_ref;
  972                 simple_unlock(&anon->an_lock);
  973 
  974                 if (refs == 0) {
  975                         uvm_anfree(anon);
  976                 }
  977         }
  978 }
  979 
  980 /*
  981  * uvm_unloanpage: kill loans on pages loaned out to the kernel
  982  *
  983  * => we expect all our resources to be unlocked
  984  */
  985 
  986 static void
  987 uvm_unloanpage(ploans, npages)
  988         struct vm_page **ploans;
  989         int npages;
  990 {
  991         struct vm_page *pg;
  992         struct simplelock *slock;
  993 
  994         uvm_lock_pageq();
  995         while (npages-- > 0) {
  996                 pg = *ploans++;
  997 
  998                 /*
  999                  * do a little dance to acquire the object or anon lock
 1000                  * as appropriate.  we are locking in the wrong order,
 1001                  * so we have to do a try-lock here.
 1002                  */
 1003 
 1004                 slock = NULL;
 1005                 while (pg->uobject != NULL || pg->uanon != NULL) {
 1006                         if (pg->uobject != NULL) {
 1007                                 slock = &pg->uobject->vmobjlock;
 1008                         } else {
 1009                                 slock = &pg->uanon->an_lock;
 1010                         }
 1011                         if (simple_lock_try(slock)) {
 1012                                 break;
 1013                         }
 1014                         uvm_unlock_pageq();
 1015                         uvm_lock_pageq();
 1016                         slock = NULL;
 1017                 }
 1018 
 1019                 /*
 1020                  * drop our loan.  if page is owned by an anon but
 1021                  * PQ_ANON is not set, the page was loaned to the anon
 1022                  * from an object which dropped ownership, so resolve
 1023                  * this by turning the anon's loan into real ownership
 1024                  * (ie. decrement loan_count again and set PQ_ANON).
 1025                  * after all this, if there are no loans left, put the
 1026                  * page back a paging queue (if the page is owned by
 1027                  * an anon) or free it (if the page is now unowned).
 1028                  */
 1029 
 1030                 KASSERT(pg->loan_count > 0);
 1031                 pg->loan_count--;
 1032                 if (pg->uobject == NULL && pg->uanon != NULL &&
 1033                     (pg->pqflags & PQ_ANON) == 0) {
 1034                         KASSERT(pg->loan_count > 0);
 1035                         pg->loan_count--;
 1036                         pg->pqflags |= PQ_ANON;
 1037                 }
 1038                 if (pg->loan_count == 0) {
 1039                         if (pg->uobject == NULL && pg->uanon == NULL) {
 1040                                 KASSERT((pg->flags & PG_BUSY) == 0);
 1041                                 uvm_pagefree(pg);
 1042                         } else {
 1043                                 uvm_pageactivate(pg);
 1044                         }
 1045                 } else if (pg->loan_count == 1 && pg->uobject != NULL &&
 1046                            pg->uanon != NULL) {
 1047                         uvm_pageactivate(pg);
 1048                 }
 1049                 if (slock != NULL) {
 1050                         simple_unlock(slock);
 1051                 }
 1052         }
 1053         uvm_unlock_pageq();
 1054 }
 1055 
 1056 /*
 1057  * uvm_unloan: kill loans on pages or anons.
 1058  */
 1059 
 1060 void
 1061 uvm_unloan(void *v, int npages, int flags)
 1062 {
 1063         if (flags & UVM_LOAN_TOANON) {
 1064                 uvm_unloananon(v, npages);
 1065         } else {
 1066                 uvm_unloanpage(v, npages);
 1067         }
 1068 }
 1069 
 1070 /*
 1071  * Minimal pager for uvm_loanzero_object.  We need to provide a "put"
 1072  * method, because the page can end up on a paging queue, and the
 1073  * page daemon will want to call pgo_put when it encounters the page
 1074  * on the inactive list.
 1075  */
 1076 
 1077 static int
 1078 ulz_put(struct uvm_object *uobj, voff_t start, voff_t stop, int flags)
 1079 {
 1080         struct vm_page *pg;
 1081 
 1082         KDASSERT(uobj == &uvm_loanzero_object);
 1083 
 1084         /*
 1085          * Don't need to do any work here if we're not freeing pages.
 1086          */
 1087 
 1088         if ((flags & PGO_FREE) == 0) {
 1089                 simple_unlock(&uobj->vmobjlock);
 1090                 return 0;
 1091         }
 1092 
 1093         /*
 1094          * we don't actually want to ever free the uvm_loanzero_page, so
 1095          * just reactivate or dequeue it.
 1096          */
 1097 
 1098         pg = TAILQ_FIRST(&uobj->memq);
 1099         KASSERT(pg != NULL);
 1100         KASSERT(TAILQ_NEXT(pg, listq) == NULL);
 1101 
 1102         uvm_lock_pageq();
 1103         if (pg->uanon)
 1104                 uvm_pageactivate(pg);
 1105         else
 1106                 uvm_pagedequeue(pg);
 1107         uvm_unlock_pageq();
 1108 
 1109         simple_unlock(&uobj->vmobjlock);
 1110         return 0;
 1111 }
 1112 
 1113 static struct uvm_pagerops ulz_pager = {
 1114         NULL,           /* init */
 1115         NULL,           /* reference */
 1116         NULL,           /* detach */
 1117         NULL,           /* fault */
 1118         NULL,           /* get */
 1119         ulz_put,        /* put */
 1120 };
 1121 
 1122 /*
 1123  * uvm_loan_init(): initialize the uvm_loan() facility.
 1124  */
 1125 
 1126 void
 1127 uvm_loan_init(void)
 1128 {
 1129 
 1130         simple_lock_init(&uvm_loanzero_object.vmobjlock);
 1131         TAILQ_INIT(&uvm_loanzero_object.memq);
 1132         uvm_loanzero_object.pgops = &ulz_pager;
 1133 
 1134         UVMHIST_INIT(loanhist, 300);
 1135 }
 1136 
 1137 /*
 1138  * uvm_loanbreak: break loan on a uobj page
 1139  *
 1140  * => called with uobj locked
 1141  * => the page should be busy
 1142  * => return value:
 1143  *      newly allocated page if succeeded
 1144  */
 1145 struct vm_page *
 1146 uvm_loanbreak(struct vm_page *uobjpage)
 1147 {
 1148         struct vm_page *pg;
 1149 #ifdef DIAGNOSTIC
 1150         struct uvm_object *uobj = uobjpage->uobject;
 1151 #endif
 1152 
 1153         KASSERT(uobj != NULL);
 1154         LOCK_ASSERT(simple_lock_held(&uobj->vmobjlock));
 1155         KASSERT(uobjpage->flags & PG_BUSY);
 1156 
 1157         /* alloc new un-owned page */
 1158         pg = uvm_pagealloc(NULL, 0, NULL, 0);
 1159         if (pg == NULL)
 1160                 return NULL;
 1161 
 1162         /*
 1163          * copy the data from the old page to the new
 1164          * one and clear the fake/clean flags on the
 1165          * new page (keep it busy).  force a reload
 1166          * of the old page by clearing it from all
 1167          * pmaps.  then lock the page queues to
 1168          * rename the pages.
 1169          */
 1170 
 1171         uvm_pagecopy(uobjpage, pg);     /* old -> new */
 1172         pg->flags &= ~(PG_FAKE|PG_CLEAN);
 1173         pmap_page_protect(uobjpage, VM_PROT_NONE);
 1174         if (uobjpage->flags & PG_WANTED)
 1175                 wakeup(uobjpage);
 1176         /* uobj still locked */
 1177         uobjpage->flags &= ~(PG_WANTED|PG_BUSY);
 1178         UVM_PAGE_OWN(uobjpage, NULL);
 1179 
 1180         uvm_lock_pageq();
 1181 
 1182         /*
 1183          * replace uobjpage with new page.
 1184          */
 1185 
 1186         uvm_pagereplace(uobjpage, pg);
 1187 
 1188         /*
 1189          * if the page is no longer referenced by
 1190          * an anon (i.e. we are breaking an O->K
 1191          * loan), then remove it from any pageq's.
 1192          */
 1193         if (uobjpage->uanon == NULL)
 1194                 uvm_pagedequeue(uobjpage);
 1195 
 1196         /*
 1197          * at this point we have absolutely no
 1198          * control over uobjpage
 1199          */
 1200 
 1201         /* install new page */
 1202         uvm_pageactivate(pg);
 1203         uvm_unlock_pageq();
 1204 
 1205         /*
 1206          * done!  loan is broken and "pg" is
 1207          * PG_BUSY.   it can now replace uobjpage.
 1208          */
 1209 
 1210         return pg;
 1211 }

Cache object: a18044c7f381d6ea4ddc290d45ee003d


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