/* $NetBSD: uvm_loan.c,v 1.69.2.1 2007/12/04 13:04:00 ad 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. * 3. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by Charles D. Cranor and * Washington University. * 4. The name of the author may not be used to endorse or promote products * derived from this software without specific prior written permission. * * 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. * * from: Id: uvm_loan.c,v 1.1.6.4 1998/02/06 05:08:43 chs Exp */ /* * uvm_loan.c: page loanout handler */ #include __KERNEL_RCSID(0, "$NetBSD: uvm_loan.c,v 1.69.2.1 2007/12/04 13:04:00 ad Exp $"); #include #include #include #include #include #include #include /* * "loaned" pages are pages which are (read-only, copy-on-write) loaned * from the VM system to other parts of the kernel. this allows page * copying to be avoided (e.g. you can loan pages from objs/anons to * the mbuf system). * * there are 3 types of loans possible: * O->K uvm_object page to wired kernel page (e.g. mbuf data area) * A->K anon page to wired kernel page (e.g. mbuf data area) * O->A uvm_object to anon loan (e.g. vnode page to an anon) * note that it possible to have an O page loaned to both an A and K * at the same time. * * loans are tracked by pg->loan_count. an O->A page will have both * a uvm_object and a vm_anon, but PQ_ANON will not be set. this sort * of page is considered "owned" by the uvm_object (not the anon). * * each loan of a page to the kernel bumps the pg->wire_count. the * kernel mappings for these pages will be read-only and wired. since * the page will also be wired, it will not be a candidate for pageout, * and thus will never be pmap_page_protect()'d with VM_PROT_NONE. a * write fault in the kernel to one of these pages will not cause * copy-on-write. instead, the page fault is considered fatal. this * is because the kernel mapping will have no way to look up the * object/anon which the page is owned by. this is a good side-effect, * since a kernel write to a loaned page is an error. * * owners that want to free their pages and discover that they are * loaned out simply "disown" them (the page becomes an orphan). these * pages should be freed when the last loan is dropped. in some cases * an anon may "adopt" an orphaned page. * * locking: to read pg->loan_count either the owner or the page queues * must be locked. to modify pg->loan_count, both the owner of the page * and the PQs must be locked. pg->flags is (as always) locked by * the owner of the page. * * note that locking from the "loaned" side is tricky since the object * getting the loaned page has no reference to the page's owner and thus * the owner could "die" at any time. in order to prevent the owner * from dying the page queues should be locked. this forces us to sometimes * use "try" locking. * * loans are typically broken by the following events: * 1. user-level xwrite fault to a loaned page * 2. pageout of clean+inactive O->A loaned page * 3. owner frees page (e.g. pager flush) * * note that loaning a page causes all mappings of the page to become * read-only (via pmap_page_protect). this could have an unexpected * effect on normal "wired" pages if one is not careful (XXX). */ /* * local prototypes */ static int uvm_loananon(struct uvm_faultinfo *, void ***, int, struct vm_anon *); static int uvm_loanuobj(struct uvm_faultinfo *, void ***, int, vaddr_t); static int uvm_loanzero(struct uvm_faultinfo *, void ***, int); static void uvm_unloananon(struct vm_anon **, int); static void uvm_unloanpage(struct vm_page **, int); static int uvm_loanpage(struct vm_page **, int); /* * inlines */ /* * uvm_loanentry: loan out pages in a map entry (helper fn for uvm_loan()) * * => "ufi" is the result of a successful map lookup (meaning that * on entry the map is locked by the caller) * => we may unlock and then relock the map if needed (for I/O) * => we put our output result in "output" * => we always return with the map unlocked * => possible return values: * -1 == error, map is unlocked * 0 == map relock error (try again!), map is unlocked * >0 == number of pages we loaned, map is unlocked * * NOTE: We can live with this being an inline, because it is only called * from one place. */ static inline int uvm_loanentry(struct uvm_faultinfo *ufi, void ***output, int flags) { vaddr_t curaddr = ufi->orig_rvaddr; vsize_t togo = ufi->size; struct vm_aref *aref = &ufi->entry->aref; struct uvm_object *uobj = ufi->entry->object.uvm_obj; struct vm_anon *anon; int rv, result = 0; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); /* * lock us the rest of the way down (we unlock before return) */ if (aref->ar_amap) amap_lock(aref->ar_amap); /* * loop until done */ while (togo) { /* * find the page we want. check the anon layer first. */ if (aref->ar_amap) { anon = amap_lookup(aref, curaddr - ufi->entry->start); } else { anon = NULL; } /* locked: map, amap, uobj */ if (anon) { rv = uvm_loananon(ufi, output, flags, anon); } else if (uobj) { rv = uvm_loanuobj(ufi, output, flags, curaddr); } else if (UVM_ET_ISCOPYONWRITE(ufi->entry)) { rv = uvm_loanzero(ufi, output, flags); } else { uvmfault_unlockall(ufi, aref->ar_amap, uobj, NULL); rv = -1; } /* locked: if (rv > 0) => map, amap, uobj [o.w. unlocked] */ KASSERT(rv > 0 || aref->ar_amap == NULL || !mutex_owned(&aref->ar_amap->am_l)); KASSERT(rv > 0 || uobj == NULL || !mutex_owned(&uobj->vmobjlock)); /* total failure */ if (rv < 0) { UVMHIST_LOG(loanhist, "failure %d", rv, 0,0,0); return (-1); } /* relock failed, need to do another lookup */ if (rv == 0) { UVMHIST_LOG(loanhist, "relock failure %d", result ,0,0,0); return (result); } /* * got it... advance to next page */ result++; togo -= PAGE_SIZE; curaddr += PAGE_SIZE; } /* * unlock what we locked, unlock the maps and return */ if (aref->ar_amap) amap_unlock(aref->ar_amap); uvmfault_unlockmaps(ufi, false); UVMHIST_LOG(loanhist, "done %d", result, 0,0,0); return (result); } /* * normal functions */ /* * uvm_loan: loan pages in a map out to anons or to the kernel * * => map should be unlocked * => start and len should be multiples of PAGE_SIZE * => result is either an array of anon's or vm_pages (depending on flags) * => flag values: UVM_LOAN_TOANON - loan to anons * UVM_LOAN_TOPAGE - loan to wired kernel page * one and only one of these flags must be set! * => returns 0 (success), or an appropriate error number */ int uvm_loan(struct vm_map *map, vaddr_t start, vsize_t len, void *v, int flags) { struct uvm_faultinfo ufi; void **result, **output; int rv, error; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); /* * ensure that one and only one of the flags is set */ KASSERT(((flags & UVM_LOAN_TOANON) == 0) ^ ((flags & UVM_LOAN_TOPAGE) == 0)); KASSERT((map->flags & VM_MAP_INTRSAFE) == 0); /* * "output" is a pointer to the current place to put the loaned page. */ result = v; output = &result[0]; /* start at the beginning ... */ /* * while we've got pages to do */ while (len > 0) { /* * fill in params for a call to uvmfault_lookup */ ufi.orig_map = map; ufi.orig_rvaddr = start; ufi.orig_size = len; /* * do the lookup, the only time this will fail is if we hit on * an unmapped region (an error) */ if (!uvmfault_lookup(&ufi, false)) { error = ENOENT; goto fail; } /* * map now locked. now do the loanout... */ rv = uvm_loanentry(&ufi, &output, flags); if (rv < 0) { /* all unlocked due to error */ error = EINVAL; goto fail; } /* * done! the map is unlocked. advance, if possible. * * XXXCDC: could be recoded to hold the map lock with * smarter code (but it only happens on map entry * boundaries, so it isn't that bad). */ if (rv) { rv <<= PAGE_SHIFT; len -= rv; start += rv; } } UVMHIST_LOG(loanhist, "success", 0,0,0,0); return 0; fail: /* * failed to complete loans. drop any loans and return failure code. * map is already unlocked. */ if (output - result) { if (flags & UVM_LOAN_TOANON) { uvm_unloananon((struct vm_anon **)result, output - result); } else { uvm_unloanpage((struct vm_page **)result, output - result); } } UVMHIST_LOG(loanhist, "error %d", error,0,0,0); return (error); } /* * uvm_loananon: loan a page from an anon out * * => called with map, amap, uobj locked * => return value: * -1 = fatal error, everything is unlocked, abort. * 0 = lookup in ufi went stale, everything unlocked, relookup and * try again * 1 = got it, everything still locked */ int uvm_loananon(struct uvm_faultinfo *ufi, void ***output, int flags, struct vm_anon *anon) { struct vm_page *pg; int error; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); /* * if we are loaning to "another" anon then it is easy, we just * bump the reference count on the current anon and return a * pointer to it (it becomes copy-on-write shared). */ if (flags & UVM_LOAN_TOANON) { mutex_enter(&anon->an_lock); pg = anon->an_page; if (pg && (pg->pqflags & PQ_ANON) != 0 && anon->an_ref == 1) { if (pg->wire_count > 0) { UVMHIST_LOG(loanhist, "->A wired %p", pg,0,0,0); uvmfault_unlockall(ufi, ufi->entry->aref.ar_amap, ufi->entry->object.uvm_obj, anon); return (-1); } pmap_page_protect(pg, VM_PROT_READ); } anon->an_ref++; **output = anon; (*output)++; mutex_exit(&anon->an_lock); UVMHIST_LOG(loanhist, "->A done", 0,0,0,0); return (1); } /* * we are loaning to a kernel-page. we need to get the page * resident so we can wire it. uvmfault_anonget will handle * this for us. */ mutex_enter(&anon->an_lock); error = uvmfault_anonget(ufi, ufi->entry->aref.ar_amap, anon); /* * if we were unable to get the anon, then uvmfault_anonget has * unlocked everything and returned an error code. */ if (error) { UVMHIST_LOG(loanhist, "error %d", error,0,0,0); /* need to refault (i.e. refresh our lookup) ? */ if (error == ERESTART) { return (0); } /* "try again"? sleep a bit and retry ... */ if (error == EAGAIN) { tsleep(&lbolt, PVM, "loanagain", 0); return (0); } /* otherwise flag it as an error */ return (-1); } /* * we have the page and its owner locked: do the loan now. */ pg = anon->an_page; mutex_enter(&uvm_pageqlock); if (pg->wire_count > 0) { mutex_exit(&uvm_pageqlock); UVMHIST_LOG(loanhist, "->K wired %p", pg,0,0,0); KASSERT(pg->uobject == NULL); uvmfault_unlockall(ufi, ufi->entry->aref.ar_amap, NULL, anon); return (-1); } if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); **output = pg; (*output)++; /* unlock anon and return success */ if (pg->uobject) mutex_exit(&pg->uobject->vmobjlock); mutex_exit(&anon->an_lock); UVMHIST_LOG(loanhist, "->K done", 0,0,0,0); return (1); } /* * uvm_loanpage: loan out pages to kernel (->K) * * => pages should be object-owned and the object should be locked. * => in the case of error, the object might be unlocked and relocked. * => caller should busy the pages beforehand. * => pages will be unbusied. * => fail with EBUSY if meet a wired page. */ static int uvm_loanpage(struct vm_page **pgpp, int npages) { int i; int error = 0; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); for (i = 0; i < npages; i++) { struct vm_page *pg = pgpp[i]; KASSERT(pg->uobject != NULL); KASSERT(pg->uobject == pgpp[0]->uobject); KASSERT(!(pg->flags & (PG_RELEASED|PG_PAGEOUT))); KASSERT(mutex_owned(&pg->uobject->vmobjlock)); KASSERT(pg->flags & PG_BUSY); mutex_enter(&uvm_pageqlock); if (pg->wire_count > 0) { mutex_exit(&uvm_pageqlock); UVMHIST_LOG(loanhist, "wired %p", pg,0,0,0); error = EBUSY; break; } if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); } uvm_page_unbusy(pgpp, npages); if (error) { /* * backout what we've done */ kmutex_t *slock = &pgpp[0]->uobject->vmobjlock; mutex_exit(slock); uvm_unloan(pgpp, i, UVM_LOAN_TOPAGE); mutex_enter(slock); } UVMHIST_LOG(loanhist, "done %d", error,0,0,0); return error; } /* * XXX UBC temp limit * number of pages to get at once. * should be <= MAX_READ_AHEAD in genfs_vnops.c */ #define UVM_LOAN_GET_CHUNK 16 /* * uvm_loanuobjpages: loan pages from a uobj out (O->K) * * => uobj shouldn't be locked. (we'll lock it) * => fail with EBUSY if we meet a wired page. */ int uvm_loanuobjpages(struct uvm_object *uobj, voff_t pgoff, int orignpages, struct vm_page **origpgpp) { int ndone; /* # of pages loaned out */ struct vm_page **pgpp; int error; int i; kmutex_t *slock; pgpp = origpgpp; for (ndone = 0; ndone < orignpages; ) { int npages; /* npendloan: # of pages busied but not loand out yet. */ int npendloan = 0xdead; /* XXX gcc */ reget: npages = MIN(UVM_LOAN_GET_CHUNK, orignpages - ndone); mutex_enter(&uobj->vmobjlock); error = (*uobj->pgops->pgo_get)(uobj, pgoff + (ndone << PAGE_SHIFT), pgpp, &npages, 0, VM_PROT_READ, 0, PGO_SYNCIO); if (error == EAGAIN) { tsleep(&lbolt, PVM, "nfsread", 0); continue; } if (error) goto fail; KASSERT(npages > 0); /* loan and unbusy pages */ slock = NULL; for (i = 0; i < npages; i++) { kmutex_t *nextslock; /* slock for next page */ struct vm_page *pg = *pgpp; /* XXX assuming that the page is owned by uobj */ KASSERT(pg->uobject != NULL); nextslock = &pg->uobject->vmobjlock; if (slock != nextslock) { if (slock) { KASSERT(npendloan > 0); error = uvm_loanpage(pgpp - npendloan, npendloan); mutex_exit(slock); if (error) goto fail; ndone += npendloan; KASSERT(origpgpp + ndone == pgpp); } slock = nextslock; npendloan = 0; mutex_enter(slock); } if ((pg->flags & PG_RELEASED) != 0) { /* * release pages and try again. */ mutex_exit(slock); for (; i < npages; i++) { pg = pgpp[i]; slock = &pg->uobject->vmobjlock; mutex_enter(slock); mutex_enter(&uvm_pageqlock); uvm_page_unbusy(&pg, 1); mutex_exit(&uvm_pageqlock); mutex_exit(slock); } goto reget; } npendloan++; pgpp++; KASSERT(origpgpp + ndone + npendloan == pgpp); } KASSERT(slock != NULL); KASSERT(npendloan > 0); error = uvm_loanpage(pgpp - npendloan, npendloan); mutex_exit(slock); if (error) goto fail; ndone += npendloan; KASSERT(origpgpp + ndone == pgpp); } return 0; fail: uvm_unloan(origpgpp, ndone, UVM_LOAN_TOPAGE); return error; } /* * uvm_loanuobj: loan a page from a uobj out * * => called with map, amap, uobj locked * => return value: * -1 = fatal error, everything is unlocked, abort. * 0 = lookup in ufi went stale, everything unlocked, relookup and * try again * 1 = got it, everything still locked */ static int uvm_loanuobj(struct uvm_faultinfo *ufi, void ***output, int flags, vaddr_t va) { struct vm_amap *amap = ufi->entry->aref.ar_amap; struct uvm_object *uobj = ufi->entry->object.uvm_obj; struct vm_page *pg; struct vm_anon *anon; int error, npages; bool locked; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); /* * first we must make sure the page is resident. * * XXXCDC: duplicate code with uvm_fault(). */ mutex_enter(&uobj->vmobjlock); if (uobj->pgops->pgo_get) { /* try locked pgo_get */ npages = 1; pg = NULL; error = (*uobj->pgops->pgo_get)(uobj, va - ufi->entry->start + ufi->entry->offset, &pg, &npages, 0, VM_PROT_READ, MADV_NORMAL, PGO_LOCKED); } else { error = EIO; /* must have pgo_get op */ } /* * check the result of the locked pgo_get. if there is a problem, * then we fail the loan. */ if (error && error != EBUSY) { uvmfault_unlockall(ufi, amap, uobj, NULL); return (-1); } /* * if we need to unlock for I/O, do so now. */ if (error == EBUSY) { uvmfault_unlockall(ufi, amap, NULL, NULL); /* locked: uobj */ npages = 1; error = (*uobj->pgops->pgo_get)(uobj, va - ufi->entry->start + ufi->entry->offset, &pg, &npages, 0, VM_PROT_READ, MADV_NORMAL, PGO_SYNCIO); /* locked: */ if (error) { if (error == EAGAIN) { tsleep(&lbolt, PVM, "fltagain2", 0); return (0); } return (-1); } /* * pgo_get was a success. attempt to relock everything. */ locked = uvmfault_relock(ufi); if (locked && amap) amap_lock(amap); uobj = pg->uobject; mutex_enter(&uobj->vmobjlock); /* * verify that the page has not be released and re-verify * that amap slot is still free. if there is a problem we * drop our lock (thus force a lookup refresh/retry). */ if ((pg->flags & PG_RELEASED) != 0 || (locked && amap && amap_lookup(&ufi->entry->aref, ufi->orig_rvaddr - ufi->entry->start))) { if (locked) uvmfault_unlockall(ufi, amap, NULL, NULL); locked = false; } /* * didn't get the lock? release the page and retry. */ if (locked == false) { if (pg->flags & PG_WANTED) { wakeup(pg); } if (pg->flags & PG_RELEASED) { mutex_enter(&uvm_pageqlock); uvm_pagefree(pg); mutex_exit(&uvm_pageqlock); mutex_exit(&uobj->vmobjlock); return (0); } mutex_enter(&uvm_pageqlock); uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); pg->flags &= ~(PG_BUSY|PG_WANTED); UVM_PAGE_OWN(pg, NULL); mutex_exit(&uobj->vmobjlock); return (0); } } KASSERT(uobj == pg->uobject); /* * at this point we have the page we want ("pg") marked PG_BUSY for us * and we have all data structures locked. do the loanout. page can * not be PG_RELEASED (we caught this above). */ if ((flags & UVM_LOAN_TOANON) == 0) { if (uvm_loanpage(&pg, 1)) { uvmfault_unlockall(ufi, amap, uobj, NULL); return (-1); } mutex_exit(&uobj->vmobjlock); **output = pg; (*output)++; return (1); } /* * must be a loan to an anon. check to see if there is already * an anon associated with this page. if so, then just return * a reference to this object. the page should already be * mapped read-only because it is already on loan. */ if (pg->uanon) { anon = pg->uanon; mutex_enter(&anon->an_lock); anon->an_ref++; mutex_exit(&anon->an_lock); if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); mutex_exit(&uobj->vmobjlock); **output = anon; (*output)++; return (1); } /* * need to allocate a new anon */ anon = uvm_analloc(); if (anon == NULL) { goto fail; } anon->an_page = pg; pg->uanon = anon; mutex_enter(&uvm_pageqlock); if (pg->wire_count > 0) { mutex_exit(&uvm_pageqlock); UVMHIST_LOG(loanhist, "wired %p", pg,0,0,0); pg->uanon = NULL; anon->an_page = NULL; anon->an_ref--; mutex_exit(&anon->an_lock); uvm_anfree(anon); goto fail; } if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); mutex_exit(&uobj->vmobjlock); mutex_exit(&anon->an_lock); **output = anon; (*output)++; return (1); fail: UVMHIST_LOG(loanhist, "fail", 0,0,0,0); /* * unlock everything and bail out. */ if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); uvmfault_unlockall(ufi, amap, uobj, NULL); return (-1); } /* * uvm_loanzero: loan a zero-fill page out * * => called with map, amap, uobj locked * => return value: * -1 = fatal error, everything is unlocked, abort. * 0 = lookup in ufi went stale, everything unlocked, relookup and * try again * 1 = got it, everything still locked */ static struct uvm_object uvm_loanzero_object; static int uvm_loanzero(struct uvm_faultinfo *ufi, void ***output, int flags) { struct vm_anon *anon; struct vm_page *pg; struct vm_amap *amap = ufi->entry->aref.ar_amap; UVMHIST_FUNC(__func__); UVMHIST_CALLED(loanhist); again: mutex_enter(&uvm_loanzero_object.vmobjlock); /* * first, get ahold of our single zero page. */ if (__predict_false((pg = TAILQ_FIRST(&uvm_loanzero_object.memq)) == NULL)) { while ((pg = uvm_pagealloc(&uvm_loanzero_object, 0, NULL, UVM_PGA_ZERO)) == NULL) { mutex_exit(&uvm_loanzero_object.vmobjlock); uvmfault_unlockall(ufi, amap, NULL, NULL); uvm_wait("loanzero"); if (!uvmfault_relock(ufi)) { return (0); } if (amap) { amap_lock(amap); } goto again; } /* got a zero'd page. */ pg->flags &= ~(PG_WANTED|PG_BUSY|PG_FAKE); pg->flags |= PG_RDONLY; mutex_enter(&uvm_pageqlock); uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); UVM_PAGE_OWN(pg, NULL); } if ((flags & UVM_LOAN_TOANON) == 0) { /* loaning to kernel-page */ mutex_enter(&uvm_pageqlock); pg->loan_count++; mutex_exit(&uvm_pageqlock); mutex_exit(&uvm_loanzero_object.vmobjlock); **output = pg; (*output)++; return (1); } /* * loaning to an anon. check to see if there is already an anon * associated with this page. if so, then just return a reference * to this object. */ if (pg->uanon) { anon = pg->uanon; mutex_enter(&anon->an_lock); anon->an_ref++; mutex_exit(&anon->an_lock); mutex_exit(&uvm_loanzero_object.vmobjlock); **output = anon; (*output)++; return (1); } /* * need to allocate a new anon */ anon = uvm_analloc(); if (anon == NULL) { /* out of swap causes us to fail */ mutex_exit(&uvm_loanzero_object.vmobjlock); uvmfault_unlockall(ufi, amap, NULL, NULL); return (-1); } anon->an_page = pg; pg->uanon = anon; mutex_enter(&uvm_pageqlock); pg->loan_count++; uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); mutex_exit(&anon->an_lock); mutex_exit(&uvm_loanzero_object.vmobjlock); **output = anon; (*output)++; return (1); } /* * uvm_unloananon: kill loans on anons (basically a normal ref drop) * * => we expect all our resources to be unlocked */ static void uvm_unloananon(struct vm_anon **aloans, int nanons) { struct vm_anon *anon; while (nanons-- > 0) { int refs; anon = *aloans++; mutex_enter(&anon->an_lock); refs = --anon->an_ref; mutex_exit(&anon->an_lock); if (refs == 0) { uvm_anfree(anon); } } } /* * uvm_unloanpage: kill loans on pages loaned out to the kernel * * => we expect all our resources to be unlocked */ static void uvm_unloanpage(struct vm_page **ploans, int npages) { struct vm_page *pg; kmutex_t *slock; mutex_enter(&uvm_pageqlock); while (npages-- > 0) { pg = *ploans++; /* * do a little dance to acquire the object or anon lock * as appropriate. we are locking in the wrong order, * so we have to do a try-lock here. */ slock = NULL; while (pg->uobject != NULL || pg->uanon != NULL) { if (pg->uobject != NULL) { slock = &pg->uobject->vmobjlock; } else { slock = &pg->uanon->an_lock; } if (mutex_tryenter(slock)) { break; } mutex_exit(&uvm_pageqlock); /* XXX Better than yielding but inadequate. */ kpause("livelock", false, 1, NULL); mutex_enter(&uvm_pageqlock); slock = NULL; } /* * drop our loan. if page is owned by an anon but * PQ_ANON is not set, the page was loaned to the anon * from an object which dropped ownership, so resolve * this by turning the anon's loan into real ownership * (ie. decrement loan_count again and set PQ_ANON). * after all this, if there are no loans left, put the * page back a paging queue (if the page is owned by * an anon) or free it (if the page is now unowned). */ KASSERT(pg->loan_count > 0); pg->loan_count--; if (pg->uobject == NULL && pg->uanon != NULL && (pg->pqflags & PQ_ANON) == 0) { KASSERT(pg->loan_count > 0); pg->loan_count--; pg->pqflags |= PQ_ANON; } if (pg->loan_count == 0 && pg->uobject == NULL && pg->uanon == NULL) { KASSERT((pg->flags & PG_BUSY) == 0); uvm_pagefree(pg); } if (slock != NULL) { mutex_exit(slock); } } mutex_exit(&uvm_pageqlock); } /* * uvm_unloan: kill loans on pages or anons. */ void uvm_unloan(void *v, int npages, int flags) { if (flags & UVM_LOAN_TOANON) { uvm_unloananon(v, npages); } else { uvm_unloanpage(v, npages); } } /* * Minimal pager for uvm_loanzero_object. We need to provide a "put" * method, because the page can end up on a paging queue, and the * page daemon will want to call pgo_put when it encounters the page * on the inactive list. */ static int ulz_put(struct uvm_object *uobj, voff_t start, voff_t stop, int flags) { struct vm_page *pg; KDASSERT(uobj == &uvm_loanzero_object); /* * Don't need to do any work here if we're not freeing pages. */ if ((flags & PGO_FREE) == 0) { mutex_exit(&uobj->vmobjlock); return 0; } /* * we don't actually want to ever free the uvm_loanzero_page, so * just reactivate or dequeue it. */ pg = TAILQ_FIRST(&uobj->memq); KASSERT(pg != NULL); KASSERT(TAILQ_NEXT(pg, listq) == NULL); mutex_enter(&uvm_pageqlock); if (pg->uanon) uvm_pageactivate(pg); else uvm_pagedequeue(pg); mutex_exit(&uvm_pageqlock); mutex_exit(&uobj->vmobjlock); return 0; } static const struct uvm_pagerops ulz_pager = { .pgo_put = ulz_put, }; /* * uvm_loan_init(): initialize the uvm_loan() facility. */ void uvm_loan_init(void) { mutex_init(&uvm_loanzero_object.vmobjlock, MUTEX_DEFAULT, IPL_NONE); TAILQ_INIT(&uvm_loanzero_object.memq); uvm_loanzero_object.pgops = &ulz_pager; UVMHIST_INIT(loanhist, 300); } /* * uvm_loanbreak: break loan on a uobj page * * => called with uobj locked * => the page should be busy * => return value: * newly allocated page if succeeded */ struct vm_page * uvm_loanbreak(struct vm_page *uobjpage) { struct vm_page *pg; #ifdef DIAGNOSTIC struct uvm_object *uobj = uobjpage->uobject; #endif KASSERT(uobj != NULL); KASSERT(mutex_owned(&uobj->vmobjlock)); KASSERT(uobjpage->flags & PG_BUSY); /* alloc new un-owned page */ pg = uvm_pagealloc(NULL, 0, NULL, 0); if (pg == NULL) return NULL; /* * copy the data from the old page to the new * one and clear the fake flags on the new page (keep it busy). * force a reload of the old page by clearing it from all * pmaps. * transfer dirtiness of the old page to the new page. * then lock the page queues to rename the pages. */ uvm_pagecopy(uobjpage, pg); /* old -> new */ pg->flags &= ~PG_FAKE; pmap_page_protect(uobjpage, VM_PROT_NONE); if ((uobjpage->flags & PG_CLEAN) != 0 && !pmap_clear_modify(uobjpage)) { pmap_clear_modify(pg); pg->flags |= PG_CLEAN; } else { /* uvm_pagecopy marked it dirty */ KASSERT((pg->flags & PG_CLEAN) == 0); /* a object with a dirty page should be dirty. */ KASSERT(!UVM_OBJ_IS_CLEAN(uobj)); } if (uobjpage->flags & PG_WANTED) wakeup(uobjpage); /* uobj still locked */ uobjpage->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(uobjpage, NULL); mutex_enter(&uvm_pageqlock); /* * replace uobjpage with new page. */ uvm_pagereplace(uobjpage, pg); /* * if the page is no longer referenced by * an anon (i.e. we are breaking an O->K * loan), then remove it from any pageq's. */ if (uobjpage->uanon == NULL) uvm_pagedequeue(uobjpage); /* * at this point we have absolutely no * control over uobjpage */ /* install new page */ uvm_pageactivate(pg); mutex_exit(&uvm_pageqlock); /* * done! loan is broken and "pg" is * PG_BUSY. it can now replace uobjpage. */ return pg; }