/* $NetBSD: uvm_loan.c,v 1.40 2003/03/04 06:18:54 thorpej 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 1.40 2003/03/04 06:18:54 thorpej 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 __P((struct uvm_faultinfo *, void ***, int, struct vm_anon *)); static int uvm_loanentry __P((struct uvm_faultinfo *, void ***, int)); static int uvm_loanuobj __P((struct uvm_faultinfo *, void ***, int, vaddr_t)); static int uvm_loanzero __P((struct uvm_faultinfo *, void ***, int)); static void uvm_unloananon __P((struct vm_anon **, int)); static void uvm_unloanpage __P((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 */ static __inline int uvm_loanentry(ufi, output, flags) 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; /* * lock us the rest of the way down (we unlock before return) */ if (aref->ar_amap) amap_lock(aref->ar_amap); if (uobj) simple_lock(&uobj->vmobjlock); /* * 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 { rv = -1; } /* locked: if (rv > 0) => map, amap, uobj [o.w. unlocked] */ /* total failure */ if (rv < 0) return (-1); /* relock failed, need to do another lookup */ if (rv == 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); if (uobj) simple_unlock(&uobj->vmobjlock); uvmfault_unlockmaps(ufi, FALSE); 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(map, start, len, v, flags) struct vm_map *map; vaddr_t start; vsize_t len; void *v; int flags; { struct uvm_faultinfo ufi; void **result, **output; int rv, error; /* * 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; } } 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); } } 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(ufi, output, flags, anon) struct uvm_faultinfo *ufi; void ***output; int flags; struct vm_anon *anon; { struct vm_page *pg; int error; /* * 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) { simple_lock(&anon->an_lock); pg = anon->u.an_page; if (pg && (pg->pqflags & PQ_ANON) != 0 && anon->an_ref == 1) { pmap_page_protect(pg, VM_PROT_READ); } anon->an_ref++; **output = anon; (*output)++; simple_unlock(&anon->an_lock); 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. */ simple_lock(&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) { /* 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->u.an_page; uvm_lock_pageq(); KASSERT(pg->wire_count == 0); if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pagedequeue(pg); uvm_unlock_pageq(); **output = pg; (*output)++; /* unlock anon and return success */ if (pg->uobject) /* XXXCDC: what if this is our uobj? bad */ simple_unlock(&pg->uobject->vmobjlock); simple_unlock(&anon->an_lock); return (1); } /* * 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(ufi, output, flags, va) 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; boolean_t locked; /* * first we must make sure the page is resident. * * XXXCDC: duplicate code with uvm_fault(). */ 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); simple_lock(&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) { uvm_lock_pageq(); uvm_pagefree(pg); uvm_unlock_pageq(); return (0); } uvm_lock_pageq(); uvm_pageactivate(pg); uvm_unlock_pageq(); pg->flags &= ~(PG_BUSY|PG_WANTED); UVM_PAGE_OWN(pg, NULL); simple_unlock(&uobj->vmobjlock); return (0); } } /* * 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) { uvm_lock_pageq(); if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pagedequeue(pg); uvm_unlock_pageq(); if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); **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; simple_lock(&anon->an_lock); anon->an_ref++; simple_unlock(&anon->an_lock); if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); **output = anon; (*output)++; return (1); } /* * need to allocate a new anon */ anon = uvm_analloc(); if (anon == NULL) { 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); } anon->u.an_page = pg; pg->uanon = anon; uvm_lock_pageq(); if (pg->loan_count == 0) { pmap_page_protect(pg, VM_PROT_READ); } pg->loan_count++; uvm_pageactivate(pg); uvm_unlock_pageq(); if (pg->flags & PG_WANTED) { wakeup(pg); } pg->flags &= ~(PG_WANTED|PG_BUSY); UVM_PAGE_OWN(pg, NULL); simple_unlock(&anon->an_lock); **output = anon; (*output)++; 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(ufi, output, flags) struct uvm_faultinfo *ufi; void ***output; int flags; { struct vm_anon *anon; struct vm_page *pg; struct uvm_object *uobj = ufi->entry->object.uvm_obj; struct vm_amap *amap = ufi->entry->aref.ar_amap; simple_lock(&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) { simple_unlock(&uvm_loanzero_object.vmobjlock); uvmfault_unlockall(ufi, amap, uobj, NULL); uvm_wait("loanzero"); if (!uvmfault_relock(ufi)) { return (0); } if (amap) { amap_lock(amap); } if (uobj) { simple_lock(&uobj->vmobjlock); } simple_lock(&uvm_loanzero_object.vmobjlock); } /* got a zero'd page. */ pg->flags &= ~(PG_WANTED|PG_BUSY|PG_FAKE); pg->flags |= PG_RDONLY; UVM_PAGE_OWN(pg, NULL); } if ((flags & UVM_LOAN_TOANON) == 0) { /* loaning to kernel-page */ uvm_lock_pageq(); pg->loan_count++; uvm_unlock_pageq(); simple_unlock(&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; simple_lock(&anon->an_lock); anon->an_ref++; simple_unlock(&anon->an_lock); simple_unlock(&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 */ simple_unlock(&uvm_loanzero_object.vmobjlock); uvmfault_unlockall(ufi, amap, uobj, NULL); return (-1); } anon->u.an_page = pg; pg->uanon = anon; uvm_lock_pageq(); pg->loan_count++; uvm_pageactivate(pg); uvm_unlock_pageq(); simple_unlock(&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(aloans, nanons) struct vm_anon **aloans; int nanons; { struct vm_anon *anon; while (nanons-- > 0) { int refs; anon = *aloans++; simple_lock(&anon->an_lock); refs = --anon->an_ref; simple_unlock(&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(ploans, npages) struct vm_page **ploans; int npages; { struct vm_page *pg; struct simplelock *slock; uvm_lock_pageq(); 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 (simple_lock_try(slock)) { break; } uvm_unlock_pageq(); uvm_lock_pageq(); 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) { if (pg->uobject == NULL && pg->uanon == NULL) { KASSERT((pg->flags & PG_BUSY) == 0); uvm_pagefree(pg); } else { uvm_pageactivate(pg); } } else if (pg->loan_count == 1 && pg->uobject != NULL && pg->uanon != NULL) { uvm_pageactivate(pg); } if (slock != NULL) { simple_unlock(slock); } } uvm_unlock_pageq(); } /* * 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); } } /* * uvm_loan_init(): initialize the uvm_loan() facility. */ void uvm_loan_init(void) { simple_lock_init(&uvm_loanzero_object.vmobjlock); TAILQ_INIT(&uvm_loanzero_object.memq); }