Skomentowany plik memory.c
polskie komentarze:
Jakub Posiadała (początek)
Jarosław Kowalski (błędy braku i ochrony strony)
/* * linux/mm/memory.c * * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds */ /* * demand-loading started 01.12.91 - seems it is high on the list of * things wanted, and it should be easy to implement. - Linus */ /* * Ok, demand-loading was easy, shared pages a little bit tricker. Shared * pages started 02.12.91, seems to work. - Linus. * * Tested sharing by executing about 30 /bin/sh: under the old kernel it * would have taken more than the 6M I have free, but it worked well as * far as I could see. * * Also corrected some "invalidate()"s - I wasn't doing enough of them. */ /* * Real VM (paging to/from disk) started 18.12.91. Much more work and * thought has to go into this. Oh, well.. * 19.12.91 - works, somewhat. Sometimes I get faults, don't know why. * Found it. Everything seems to work now. * 20.12.91 - Ok, making the swap-device changeable like the root. */ /* * 05.04.94 - Multi-page memory management added for v1.1. * Idea by Alex Bligh (alex@cconcepts.co.uk) */ //====================================================================================== // SŁOWNICZEK // ważniejszych TLS-ow (TrzyLiterowych Skrotow), które udało mi się rozszyfrować // znacznie ulatwiających szybsze zrozumienie kodu // // COW COPY ON WRITE - kopiuj przy pisaniu sposób kopiownia zapobiegający // bezsensownemu przepisywaniu pustych stron - strona // jest zapisywana przy pierwszej próbie pisania // na nią // PGD (PAGE ? DIRECTORY) - katalogu tablicy ramek // PMD (PAGE ? ?) - tablica ramek // PTE (PAGE TABLE ELEMENT) - element tablicy ramek, czyli ramka (page) // zap ( to nie jest skrót) - w żargonie: zabić, usunąć // // //===================================================================================== #include <linux/signal.h> #include <linux/sched.h> #include <linux/head.h> #include <linux/kernel.h> #include <linux/errno.h> #include <linux/string.h> #include <linux/types.h> #include <linux/ptrace.h> #include <linux/mman.h> #include <linux/mm.h> #include <linux/swap.h> #include <asm/system.h> #include <asm/segment.h> #include <asm/pgtable.h> #include <asm/string.h> unsigned long high_memory = 0; /* * We special-case the C-O-W ZERO_PAGE, because it's such * a common occurrence (no need to read the page to know * that it's zero - better for the cache and memory subsystem). */ //=============================================================================== // Funkcja kopiujaca ramkę ze szczegolnym potraktowaniem przypadku kopiowania // "ramki zerowej" // Ramka zerowa (ZERO_PAGE) służy do inicjowania pamięci //=============================================================================== static inline void copy_page(unsigned long from, unsigned long to) { if (from == ZERO_PAGE) { memset((void *) to, 0, PAGE_SIZE); return; } memcpy((void *) to, (void *) from, PAGE_SIZE); } //============================================================================ // USER_PTRS_PER_PGD określa ile elementów katalogu tablicy stron (pgd) // jest przyporządkowanych danemu procesowi //============================================================================ #define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE) mem_map_t * mem_map = NULL; /* * oom() prints a message (so that the user knows why the process died), * and gives the process an untrappable SIGKILL. */
//=================================================================================== // Funkcja wypisuje komunikat i wysyła nieprzechwytywalny sygnał // SIGKILL do procesu, który jest argumentem //==================================================================================== void oom(struct task_struct * task) { printk("\nOut of memory for %s.\n", task->comm); task->sig->action[SIGKILL-1].sa_handler = NULL; task->blocked &= ~(1<<(SIGKILL-1)); send_sig(SIGKILL,task,1); } /* * Note: this doesn't free the actual pages themselves. That * has been handled earlier when unmapping all the memory regions. */ //=================================================================================== // Po sprawdzeniu poprawności ramki zwalnia ją wywołując // pte_free z pliku pgtable.h , która z kolei nie robi nic innego, // tylko wywołuje free_page z page_alloc.c - funkcję rzeczywiście // zwalnijącą ramki //============================================================================== static inline void free_one_pmd(pmd_t * dir) { pte_t * pte; if (pmd_none(*dir)) return; if (pmd_bad(*dir)) { printk("free_one_pmd: bad directory entry %08lx\n", pmd_val(*dir)); pmd_clear(dir); return; } pte = pte_offset(dir, 0); pmd_clear(dir); pte_free(pte); } //================================================================================= // Funkcja działa analogicznie jak poprzednia, z tym, że zwalnia strukturę // o poziom wyższą. // Z pliku pgtable.h,możemy się dowiedzieć,że na procesorze i386 podział na // trzy poziomy pamięci jest jedynie markowany, więc funkcje, które rozróżniają^Ú // PMD i PGD są zaprojektowane na przyszłość. //================================================================================= static inline void free_one_pgd(pgd_t * dir) { int j; pmd_t * pmd; if (pgd_none(*dir)) return; if (pgd_bad(*dir)) { printk("free_one_pgd: bad directory entry %08lx\n", pgd_val(*dir)); pgd_clear(dir); return; } pmd = pmd_offset(dir, 0); pgd_clear(dir); for (j = 0; j < PTRS_PER_PMD ; j++) free_one_pmd(pmd+j); pmd_free(pmd); } /* * This function clears all user-level page tables of a process - this * is needed by execve(), so that old pages aren't in the way. */ //============================================================================== // // Zwalnia (spławia) wszystkie ramki (z poziomu użytkownika) // danego procesu. Funkcje zwalniające pamięć podręczną flush_xxx // na proscesorze i386 są puste, procesor sam ją czyści // //============================================================================= void clear_page_tables(struct task_struct * tsk) { int i; pgd_t * page_dir; page_dir = tsk->mm->pgd; if (!page_dir || page_dir == swapper_pg_dir) { printk("%s trying to clear kernel page-directory: not good\n", tsk->comm); return; } flush_cache_mm(tsk->mm); for (i = 0 ; i < USER_PTRS_PER_PGD ; i++) free_one_pgd(page_dir + i); flush_tlb_mm(tsk->mm); } /* * This function frees up all page tables of a process when it exits. It * is the same as "clear_page_tables()", except it also changes the process' * page table directory to the kernel page tables and then frees the old * page table directory. */ //================================================================================ // Zachowuje się analogicznie jak poprzednia, z tym, że dodatkowo // zmienia elementy katalogu ramek procesu ( proses może mieć więcej // niż jeden pgd, ich liczba jest określona przez USER_PTRS_PER_PGD) // na element katalogu ramek jądra i zwalnia dotychczas zajmowany. // Używana przy kończeniu procesu. // //============================================================================= void free_page_tables(struct mm_struct * mm) { int i; pgd_t * page_dir; page_dir = mm->pgd; if (!page_dir || page_dir == swapper_pg_dir) { printk("Trying to free kernel page-directory: not good\n"); return; } for (i = 0 ; i < USER_PTRS_PER_PGD ; i++) free_one_pgd(page_dir + i); pgd_free(page_dir); } //============================================================================= // Tworzy nowy katalog stron dla procesu //============================================================================ int new_page_tables(struct task_struct * tsk) { pgd_t * page_dir, * new_pg; if (!(new_pg = pgd_alloc())) return -ENOMEM; page_dir = pgd_offset(&init_mm, 0); flush_cache_mm(tsk->mm); memcpy(new_pg + USER_PTRS_PER_PGD, page_dir + USER_PTRS_PER_PGD, (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof (pgd_t)); flush_tlb_mm(tsk->mm); SET_PAGE_DIR(tsk, new_pg); tsk->mm->pgd = new_pg; return 0; } //============================================================================= // Kilka poniższych funkcji służy do kopiowania,usuwania i zaznaczania // struktur pamięci.Zasada ich działania jest podobna i szczegółowe // opisywanie każdej z osobna byłoby niecelowe. // Schemat działania tych funkcji: // - sprawdzenie statusu danych; // - podjęcie adekwatnego do statusu danych i zadania funkcji działania // (kopiowania,usuwnia,bądź oznaczania danych) najczęściej przez // odwołanie się do funkcji odnoszącej się do prostszej struktury // danych // // Nagminnie używane funkcje typu pte_none, pte_present, pmd_bad, pmd_present // służą do określenia statusu ramki są zdefiniowane w pliku pgtable.h. //============================================================================= //============================================================================ // copy_one_pte - kopiuje pojedynczą ramkę. Jeśli funkcja zostanie wywołana // z argumentem cow różnym od zera ramka do której kopiujemy // zostanie oznaczona jako tylko-do-odczytu i ewentualna // próba pisania do niej spowoduje wywołanie błędu ochrony // strony. //============================================================================= static inline void copy_one_pte(pte_t * old_pte, pte_t * new_pte, int cow) { pte_t pte = *old_pte; unsigned long page_nr; if (pte_none(pte)) return; if (!pte_present(pte)) { swap_duplicate(pte_val(pte)); set_pte(new_pte, pte); return; } page_nr = MAP_NR(pte_page(pte)); if (page_nr >= MAP_NR(high_memory) || PageReserved(mem_map+page_nr)) { set_pte(new_pte, pte); return; } if (cow) pte = pte_wrprotect(pte); if (delete_from_swap_cache(page_nr)) pte = pte_mkdirty(pte); set_pte(new_pte, pte_mkold(pte)); set_pte(old_pte, pte); mem_map[page_nr].count++; } //================================================================================ // copy_pte_range - kopiuje ramki z podanego przedziału // Adres ramki nie jest podany jawnie jak w poprzedniej funkcji, podany // jest adres tablicy ramek do której ramka należy (*src_pmd) i // przesunięcie (offset) początkowej ramki względem tego adresu. // Wielkość fragmentu do skopiowania określona jest argumentem size. // Kopiujemy pojedyncze ramki uzywając poprzedniej funkcji do której jest // też przekazywany argument "cow". // Dziwne jest zachowanie tej funkcji w przypadku gdy obszar do skopiowania // jest zbyt duży - wtedy, zamiast zgłosić błąd funkcja kopiuje tyle ile // się da w obrębie aktualnego pmd i kończy działanie. // W przypadku błędu - niemożliwości zapisania do *dst_pmd // zwraca -ENOMEM (=-12). //=============================================================================== static inline int copy_pte_range(pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long address, unsigned long size, int cow) { pte_t * src_pte, * dst_pte; unsigned long end; if (pmd_none(*src_pmd)) return 0; if (pmd_bad(*src_pmd)) { printk("copy_pte_range: bad pmd (%08lx)\n", pmd_val(*src_pmd)); pmd_clear(src_pmd); return 0; } src_pte = pte_offset(src_pmd, address); if (pmd_none(*dst_pmd)) { if (!pte_alloc(dst_pmd, 0)) return -ENOMEM; } dst_pte = pte_offset(dst_pmd, address); address &= ~PMD_MASK; end = address + size; if (end >= PMD_SIZE) end = PMD_SIZE; do { /* I would like to switch arguments here, to make it * consistent with copy_xxx_range and memcpy syntax. */ copy_one_pte(src_pte++, dst_pte++, cow); address += PAGE_SIZE; } while (address < end); return 0; } //================================================================================= // copy_pmd_range - działa analogicznie jak poprzednia, z tym, że kopiowane // są nie strony, a tablice stron (pmd). // W przypadku poprawnego działania zwraca 0 w przypadu // błędu -ENOMEM (=-12) //================================================================================= static inline int copy_pmd_range(pgd_t *dst_pgd, pgd_t *src_pgd, unsigned long address, unsigned long size, int cow) { pmd_t * src_pmd, * dst_pmd; unsigned long end; int error = 0; if (pgd_none(*src_pgd)) return 0; if (pgd_bad(*src_pgd)) { printk("copy_pmd_range: bad pgd (%08lx)\n", pgd_val(*src_pgd)); pgd_clear(src_pgd); return 0; } src_pmd = pmd_offset(src_pgd, address); if (pgd_none(*dst_pgd)) { if (!pmd_alloc(dst_pgd, 0)) return -ENOMEM; } dst_pmd = pmd_offset(dst_pgd, address); address &= ~PGDIR_MASK; end = address + size; if (end > PGDIR_SIZE) end = PGDIR_SIZE; do { error = copy_pte_range(dst_pmd++, src_pmd++, address, end - address, cow); if (error) break; address = (address + PMD_SIZE) & PMD_MASK; } while (address < end); return error; } /* * copy one vm_area from one task to the other. Assumes the page tables * already present in the new task to be cleared in the whole range * covered by this vma. */ //============================================================================= // // Funkcja kopiuje strony jednego procesu innemu. // Funkcja pgd_offset znajduje pozycję mm_struct w katalogu tablicy ramek, // a później zadany obszar jest kopiowany za pomocą funkcji copy_pmd_range. // //============================================================================= int copy_page_range(struct mm_struct *dst, struct mm_struct *src, struct vm_area_struct *vma) { pgd_t * src_pgd, * dst_pgd; unsigned long address = vma->vm_start; unsigned long end = vma->vm_end; int error = 0, cow; cow = (vma->vm_flags & (VM_SHARED | VM_WRITE)) == VM_WRITE; src_pgd = pgd_offset(src, address); dst_pgd = pgd_offset(dst, address); flush_cache_range(src, vma->vm_start, vma->vm_end); flush_cache_range(dst, vma->vm_start, vma->vm_end); while (address < end) { error = copy_pmd_range(dst_pgd++, src_pgd++, address, end - address, cow); if (error) break; address = (address + PGDIR_SIZE) & PGDIR_MASK; } /* Note that the src ptes get c-o-w treatment, so they change too. */ flush_tlb_range(src, vma->vm_start, vma->vm_end); flush_tlb_range(dst, vma->vm_start, vma->vm_end); return error; } //=============================================================================== // // Funkcja zwalnia ramkę (wywołując free_page) jeżeli ramka istnieje // (page.pte <> 0) i ma ustawiony bit _PAGE_PRESENT, następnie // zmniejszana jest liczba ramek procesu, do którego ta ramka należała // (rs--), jeśli proces miał jeszcze jakieś ramki. // Ramka zostaje usuwana z pamięci w każdym przypadku. // //============================================================================== static inline void free_pte(pte_t page) { if (pte_present(page)) { unsigned long addr = pte_page(page); if (addr >= high_memory || PageReserved(mem_map+MAP_NR(addr))) return; free_page(addr); if (current->mm->rss <= 0) return; current->mm->rss--; return; } swap_free(pte_val(page)); } //============================================================================= // W przypadku gdy bit _PAGE_PRESENT nie jest zapalony tylko wypisuje // ostrzeżenie i usuwa stronę z pamięci. //============================================================================ static inline void forget_pte(pte_t page) { if (!pte_none(page)) { printk("forget_pte: old mapping existed!\n"); free_pte(page); } } //========================================================================================= // // Usuwa wszystkie ramki z podanego przedziału. Przedział określony jak // w funkcji copy_pte_range. // //================================================================================ static inline void zap_pte_range(pmd_t * pmd, unsigned long address, unsigned long size) { pte_t * pte; if (pmd_none(*pmd)) return; if (pmd_bad(*pmd)) { printk("zap_pte_range: bad pmd (%08lx)\n", pmd_val(*pmd)); pmd_clear(pmd); return; } pte = pte_offset(pmd, address); address &= ~PMD_MASK; if (address + size > PMD_SIZE) size = PMD_SIZE - address; size >>= PAGE_SHIFT; for (;;) { pte_t page; if (!size) break; page = *pte; pte++; size--; if (pte_none(page)) continue; pte_clear(pte-1); free_pte(page); } } //================================================================================== // // Zupełnie analogiczna do copy_pmd_range. // //================================================================================== static inline void zap_pmd_range(pgd_t * dir, unsigned long address, unsigned long size) { pmd_t * pmd; unsigned long end; if (pgd_none(*dir)) return; if (pgd_bad(*dir)) { printk("zap_pmd_range: bad pgd (%08lx)\n", pgd_val(*dir)); pgd_clear(dir); return; } pmd = pmd_offset(dir, address); address &= ~PGDIR_MASK; end = address + size; if (end > PGDIR_SIZE) end = PGDIR_SIZE; do { zap_pte_range(pmd, address, end - address); address = (address + PMD_SIZE) & PMD_MASK; pmd++; } while (address < end); } /* * remove user pages in a given range. */ //============================================================================== // // Usuwa z pamięci strony procesu z podanego zakresu // Uwaga: funkcje flush_xxx, zdefiniowane w pgtable.h , // służące do zwalniania pamięci podręcznej // są dla procesora i386 puste, ich rolę przejmuje procesor //============================================================================== int zap_page_range(struct mm_struct *mm, unsigned long address, unsigned long size) { pgd_t * dir; unsigned long end = address + size; dir = pgd_offset(mm, address); flush_cache_range(mm, end - size, end); while (address < end) { zap_pmd_range(dir, address, end - address); address = (address + PGDIR_SIZE) & PGDIR_MASK; dir++; } flush_tlb_range(mm, end - size, end); return 0; } //================================================================================= // // Funkcje zeromap_xxx_range ustawiają ramki pamięci z danego przedziału // na ramki zerowe. Oznacza to, że te fragmenty pamięci fizycznej // nie zawierające stron żadnego procesu. // //============================================================================== static inline void zeromap_pte_range(pte_t * pte, unsigned long address, unsigned long size, pte_t zero_pte) { unsigned long end; address &= ~PMD_MASK; end = address + size; if (end > PMD_SIZE) end = PMD_SIZE; do { pte_t oldpage = *pte; set_pte(pte, zero_pte); forget_pte(oldpage); address += PAGE_SIZE; pte++; } while (address < end); } static inline int zeromap_pmd_range(pmd_t * pmd, unsigned long address, unsigned long size, pte_t zero_pte) { unsigned long end; address &= ~PGDIR_MASK; end = address + size; if (end > PGDIR_SIZE) end = PGDIR_SIZE; do { pte_t * pte = pte_alloc(pmd, address); if (!pte) return -ENOMEM; zeromap_pte_range(pte, address, end - address, zero_pte); address = (address + PMD_SIZE) & PMD_MASK; pmd++; } while (address < end); return 0; } int zeromap_page_range(unsigned long address, unsigned long size, pgprot_t prot) { int error = 0; pgd_t * dir; unsigned long beg = address; unsigned long end = address + size; pte_t zero_pte; zero_pte = pte_wrprotect(mk_pte(ZERO_PAGE, prot)); dir = pgd_offset(current->mm, address); flush_cache_range(current->mm, beg, end); while (address < end) { pmd_t *pmd = pmd_alloc(dir, address); error = -ENOMEM; if (!pmd) break; error = zeromap_pmd_range(pmd, address, end - address, zero_pte); if (error) break; address = (address + PGDIR_SIZE) & PGDIR_MASK; dir++; } flush_tlb_range(current->mm, beg, end); return error; } /* * maps a range of physical memory into the requested pages. the old * mappings are removed. any references to nonexistent pages results * in null mappings (currently treated as "copy-on-access") */ //============================================================================== // // Funkcje remap_xxx_range odwzorowywują podany przedział pamięci fizycznej // w zadane strony. // //============================================================================== static inline void remap_pte_range(pte_t * pte, unsigned long address, unsigned long size, unsigned long offset, pgprot_t prot) { unsigned long end; address &= ~PMD_MASK; end = address + size; if (end > PMD_SIZE) end = PMD_SIZE; do { pte_t oldpage = *pte; pte_clear(pte); if (offset >= high_memory || PageReserved(mem_map+MAP_NR(offset))) set_pte(pte, mk_pte(offset, prot)); forget_pte(oldpage); address += PAGE_SIZE; offset += PAGE_SIZE; pte++; } while (address < end); } static inline int remap_pmd_range(pmd_t * pmd, unsigned long address, unsigned long size, unsigned long offset, pgprot_t prot) { unsigned long end; address &= ~PGDIR_MASK; end = address + size; if (end > PGDIR_SIZE) end = PGDIR_SIZE; offset -= address; do { pte_t * pte = pte_alloc(pmd, address); if (!pte) return -ENOMEM; remap_pte_range(pte, address, end - address, address + offset, prot); address = (address + PMD_SIZE) & PMD_MASK; pmd++; } while (address < end); return 0; } int remap_page_range(unsigned long from, unsigned long offset, unsigned long size, pgprot_t prot) { int error = 0; pgd_t * dir; unsigned long beg = from; unsigned long end = from + size; offset -= from; dir = pgd_offset(current->mm, from); flush_cache_range(current->mm, beg, end); while (from < end) { pmd_t *pmd = pmd_alloc(dir, from); error = -ENOMEM; if (!pmd) break; error = remap_pmd_range(pmd, from, end - from, offset + from, prot); if (error) break; from = (from + PGDIR_SIZE) & PGDIR_MASK; dir++; } flush_tlb_range(current->mm, beg, end); return error; } /* * sanity-check function.. */ //=========================================================================== // Wstawia ramkę do tablicy ramek //=========================================================================== static void put_page(pte_t * page_table, pte_t pte) { if (!pte_none(*page_table)) { free_page(pte_page(pte)); return; } /* no need for flush_tlb */ set_pte(page_table, pte); } /* * This routine is used to map in a page into an address space: needed by * execve() for the initial stack and environment pages. */ //================================================================================= // // Wkłada ramkę (arument page) do przestrzeni adresowej procesu (tsk) // pod wskazany adres.Jeżeli warunki sa sprzyjające tzn. uda się // odnaleźć katalog stron procesu i utworzyć w nim tablicę ramek // oraz nie istnieje juz ramka o tym adresie, to ramka zostaje zapisana // z zapalonymi bitami DIRTY i RW // //================================================================================= unsigned long put_dirty_page(struct task_struct * tsk, unsigned long page, unsigned long address) { pgd_t * pgd; pmd_t * pmd; pte_t * pte; if (page >= high_memory) printk("put_dirty_page: trying to put page %08lx at %08lx\n",page,address); if (mem_map[MAP_NR(page)].count != 1) printk("mem_map disagrees with %08lx at %08lx\n",page,address); pgd = pgd_offset(tsk->mm,address); pmd = pmd_alloc(pgd, address); if (!pmd) { free_page(page); oom(tsk); return 0; } pte = pte_alloc(pmd, address); if (!pte) { free_page(page); oom(tsk); return 0; } if (!pte_none(*pte)) { printk("put_dirty_page: page already exists\n"); free_page(page); return 0; } flush_page_to_ram(page); set_pte(pte, pte_mkwrite(pte_mkdirty(mk_pte(page, PAGE_COPY)))); /* no need for invalidate */ return page; } //============================================================================= // // FUNKCJE DOTYCZĄCE BŁĘDOW BRAKU I OCHRONY STRONY // // Skomentował: Jarosław Kowalski // //============================================================================= // ***************************************************************** // Funkcja do_wp_page // // jest wywolywana przez niskopoziomowy handler "do_page_fault" // w przypadku gdy wystapilo odwolanie do strony, do ktorej // proces nie ma praw zapisu. Ma to miejsce w przypadku // gdy strona pamieci jest dzielona lub zostala niedawno // wykonana operacja fork() i nie zostaly fizycznie skopiowane // strony procesu macierzystego do potomnego. // // ***************************************************************** /* * This routine handles present pages, when users try to write * to a shared page. It is done by copying the page to a new address * and decrementing the shared-page counter for the old page. * * Goto-purists beware: the only reason for goto's here is that it results * in better assembly code.. The "default" path will see no jumps at all. * * Note that this routine assumes that the protection checks have been * done by the caller (the low-level page fault routine in most cases). * Thus we can safely just mark it writable once we've done any necessary * COW. * * We also mark the page dirty at this point even though the page will * change only once the write actually happens. This avoids a few races, * and potentially makes it more efficient. */ void do_wp_page(struct task_struct * tsk, struct vm_area_struct * vma, unsigned long address, int write_access) { pgd_t *page_dir; pmd_t *page_middle; pte_t *page_table, pte; unsigned long old_page, new_page; // pobranie nowej strony na ktora skopiujemy nasza new_page = __get_free_page(GFP_KERNEL); // sprawdzenie i uaktualnienie struktur tablicy stron i // katalogu tablic stron page_dir = pgd_offset(vma->vm_mm, address); if (pgd_none(*page_dir)) goto end_wp_page; if (pgd_bad(*page_dir)) goto bad_wp_pagedir; page_middle = pmd_offset(page_dir, address); if (pmd_none(*page_middle)) goto end_wp_page; if (pmd_bad(*page_middle)) goto bad_wp_pagemiddle; page_table = pte_offset(page_middle, address); pte = *page_table; if (!pte_present(pte)) goto end_wp_page; if (pte_write(pte)) goto end_wp_page; old_page = pte_page(pte); // uaktualnienie statystyk if (old_page >= high_memory) goto bad_wp_page; tsk->min_flt++; // ********************************************************* // kopiujemy strone wtedy, kiedy liczba odwolan do niej // jest rozna od 1. W takim przypadku usuwamy tylko atrybut // COW - copy on write // ********************************************************* /* * Do we need to copy? */ if (mem_map[MAP_NR(old_page)].count != 1) { if (new_page) { if (PageReserved(mem_map + MAP_NR(old_page))) ++vma->vm_mm->rss; // // tutaj fizyczne kopiowanie pamieci // copy_page(old_page,new_page); flush_page_to_ram(old_page); flush_page_to_ram(new_page); flush_cache_page(vma, address); set_pte(page_table, pte_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot)))); free_page(old_page); flush_tlb_page(vma, address); return; } // // je6li nie uda3o sij przydzielif strony do skopiowania // traktujemy to jako blad i wychodzimy z bledem OUT OF // MEMORY // flush_cache_page(vma, address); set_pte(page_table, BAD_PAGE); flush_tlb_page(vma, address); free_page(old_page); oom(tsk); return; } // sprz1tamy po sobie flush_cache_page(vma, address); set_pte(page_table, pte_mkdirty(pte_mkwrite(pte))); flush_tlb_page(vma, address); if (new_page) free_page(new_page); return; // // przypadki b3jdne // bad_wp_page: printk("do_wp_page: bogus page at address %08lx (%08lx)\n",address,old_page); send_sig(SIGKILL, tsk, 1); goto end_wp_page; bad_wp_pagemiddle: printk("do_wp_page: bogus page-middle at address %08lx (%08lx)\n", address, pmd_val(*page_middle)); send_sig(SIGKILL, tsk, 1); goto end_wp_page; bad_wp_pagedir: printk("do_wp_page: bogus page-dir entry at address %08lx (%08lx)\n", address, pgd_val(*page_dir)); send_sig(SIGKILL, tsk, 1); end_wp_page: if (new_page) free_page(new_page); return; } /* * Ugly, ugly, but the goto's result in better assembly.. */ int verify_area(int type, const void * addr, unsigned long size) { struct vm_area_struct * vma; unsigned long start = (unsigned long) addr; /* If the current user space is mapped to kernel space (for the * case where we use a fake user buffer with get_fs/set_fs()) we * don't expect to find the address in the user vm map. */ if (!size || get_fs() == KERNEL_DS) return 0; vma = find_vma(current->mm, start); if (!vma) goto bad_area; if (vma->vm_start > start) goto check_stack; good_area: if (type == VERIFY_WRITE) goto check_write; for (;;) { struct vm_area_struct * next; if (!(vma->vm_flags & VM_READ)) goto bad_area; if (vma->vm_end - start >= size) return 0; next = vma->vm_next; if (!next || vma->vm_end != next->vm_start) goto bad_area; vma = next; } check_write: if (!(vma->vm_flags & VM_WRITE)) goto bad_area; if (!wp_works_ok) goto check_wp_fault_by_hand; for (;;) { if (vma->vm_end - start >= size) break; if (!vma->vm_next || vma->vm_end != vma->vm_next->vm_start) goto bad_area; vma = vma->vm_next; if (!(vma->vm_flags & VM_WRITE)) goto bad_area; } return 0; check_wp_fault_by_hand: size--; size += start & ~PAGE_MASK; size >>= PAGE_SHIFT; start &= PAGE_MASK; for (;;) { do_wp_page(current, vma, start, 1); if (!size) break; size--; start += PAGE_SIZE; if (start < vma->vm_end) continue; vma = vma->vm_next; if (!vma || vma->vm_start != start) goto bad_area; if (!(vma->vm_flags & VM_WRITE)) goto bad_area;; } return 0; check_stack: if (!(vma->vm_flags & VM_GROWSDOWN)) goto bad_area; if (expand_stack(vma, start) == 0) goto good_area; bad_area: return -EFAULT; } /* * This function zeroes out partial mmap'ed pages at truncation time.. */ static void partial_clear(struct vm_area_struct *vma, unsigned long address) { pgd_t *page_dir; pmd_t *page_middle; pte_t *page_table, pte; page_dir = pgd_offset(vma->vm_mm, address); if (pgd_none(*page_dir)) return; if (pgd_bad(*page_dir)) { printk("bad page table directory entry %p:[%lx]\n", page_dir, pgd_val(*page_dir)); pgd_clear(page_dir); return; } page_middle = pmd_offset(page_dir, address); if (pmd_none(*page_middle)) return; if (pmd_bad(*page_middle)) { printk("bad page table directory entry %p:[%lx]\n", page_dir, pgd_val(*page_dir)); pmd_clear(page_middle); return; } page_table = pte_offset(page_middle, address); pte = *page_table; if (!pte_present(pte)) return; flush_cache_page(vma, address); address &= ~PAGE_MASK; address += pte_page(pte); if (address >= high_memory) return; memset((void *) address, 0, PAGE_SIZE - (address & ~PAGE_MASK)); flush_page_to_ram(pte_page(pte)); } /* * Handle all mappings that got truncated by a "truncate()" * system call. * * NOTE! We have to be ready to update the memory sharing * between the file and the memory map for a potential last * incomplete page. Ugly, but necessary. */ void vmtruncate(struct inode * inode, unsigned long offset) { struct vm_area_struct * mpnt; truncate_inode_pages(inode, offset); if (!inode->i_mmap) return; mpnt = inode->i_mmap; do { unsigned long start = mpnt->vm_start; unsigned long len = mpnt->vm_end - start; unsigned long diff; /* mapping wholly truncated? */ if (mpnt->vm_offset >= offset) { zap_page_range(mpnt->vm_mm, start, len); continue; } /* mapping wholly unaffected? */ diff = offset - mpnt->vm_offset; if (diff >= len) continue; /* Ok, partially affected.. */ start += diff; len = (len - diff) & PAGE_MASK; if (start & ~PAGE_MASK) { partial_clear(mpnt, start); start = (start + ~PAGE_MASK) & PAGE_MASK; } zap_page_range(mpnt->vm_mm, start, len); } while ((mpnt = mpnt->vm_next_share) != inode->i_mmap); } // ********************************************************************** // funkcja wczytuje strone odpowiadajaca adresowi z urzadzenia wymiany // // jesli zdefiniowana jest specjalna procedura do tego celu w // vm_ops to jest ona wykorzystywana zamiast standardowej // ********************************************************************** static inline void do_swap_page(struct task_struct * tsk, struct vm_area_struct * vma, unsigned long address, pte_t * page_table, pte_t entry, int write_access) { pte_t page; if (!vma->vm_ops || !vma->vm_ops->swapin) { swap_in(tsk, vma, page_table, pte_val(entry), write_access); flush_page_to_ram(pte_page(*page_table)); return; } page = vma->vm_ops->swapin(vma, address - vma->vm_start + vma->vm_offset, pte_val(entry)); if (pte_val(*page_table) != pte_val(entry)) { free_page(pte_page(page)); return; } if (mem_map[MAP_NR(pte_page(page))].count > 1 && !(vma->vm_flags & VM_SHARED)) page = pte_wrprotect(page); ++vma->vm_mm->rss; ++tsk->maj_flt; flush_page_to_ram(pte_page(page)); set_pte(page_table, page); return; } // ***************************************************************** // Funkcja do_no_page // // jest wywolywana przez niskopoziomowy handler "do_page_fault" // w przypadku gdy wystapilo odwolanie do strony, ktorej // jeszcze nie ma w pamieci. Jest to wielka rozdzielnia, ktora // sprawdza stan ramki w pamieci i w zaleznosci od tego wywoluje // odpowiednie akcje: // // 1. is_present - strona znajduje sie w pamieci // (przydzielona innemu procesowi). // - uaktualnienie deskryptora strony // 2. swap_page - strona dostepna na urzadzeniu wymiany // - wczytanie z dysku // 3. anonymous_page - strona niezainicjalizowana // - pobranie nowej strony z puli systemu i uaktualnienie // deskryptorow // 4. sig_bus - nie udalo sie wczytac/przydzielic strony // - blad krytyczny // 5. oom - brak pamieci // // ***************************************************************** /* * do_no_page() tries to create a new page mapping. It aggressively * tries to share with existing pages, but makes a separate copy if * the "write_access" parameter is true in order to avoid the next * page fault. * * As this is called only for pages that do not currently exist, we * do not need to flush old virtual caches or the TLB. */ void do_no_page(struct task_struct * tsk, struct vm_area_struct * vma, unsigned long address, int write_access) { pgd_t * pgd; pmd_t * pmd; pte_t * page_table; pte_t entry; unsigned long page; // // odczytanie i ewentualne przydzielenie elementow katalogu // katalogu posredniego i tablicy stron (moglo sie zdarzyc, // ze jest to pierwsze odwolanie do strony, do ktorej nie istnieje // pozycja w katalogu ktoregos poziomu // pgd = pgd_offset(tsk->mm, address); pmd = pmd_alloc(pgd, address); if (!pmd) goto no_memory; page_table = pte_alloc(pmd, address); if (!page_table) goto no_memory; entry = *page_table; // *********************************************************** // tutaj przypadek, kiedy mamy pamiec dzielona do odczytu i // okazalo sie ze strona jest juz w pamieci // poprzednie operacje zalatwily juz uaktualnienie tablic // wiec mozemy spokojnie wyjsc nie zglaszajac bledu // *********************************************************** if (pte_present(entry)) goto is_present; // *********************************************************** // strone trzeba wczytac z dysku // *********************************************************** if (!pte_none(entry)) goto swap_page; // *********************************************************** // tutaj mamy przypadek strony anonimowej. Albo pobieramy // nowa, czysta strone z puli systemu, albo wykorzystujemy // specjalna funkcje "nopage" zwiazana z obszarem pamieci // o ile jest ona zdefiniowana // *********************************************************** address &= PAGE_MASK; if (!vma->vm_ops || !vma->vm_ops->nopage) goto anonymous_page; /* * The third argument is "no_share", which tells the low-level code * to copy, not share the page even if sharing is possible. It's * essentially an early COW detection */ page = vma->vm_ops->nopage(vma, address, (vma->vm_flags & VM_SHARED)?0:write_access); if (!page) goto sigbus; ++tsk->maj_flt; ++vma->vm_mm->rss; /* * This silly early PAGE_DIRTY setting removes a race * due to the bad i386 page protection. But it's valid * for other architectures too. * * Note that if write_access is true, we either now have * a exclusive copy of the page, or this is a shared mapping, * so we can make it writable and dirty to avoid having to * handle that later. */ flush_page_to_ram(page); entry = mk_pte(page, vma->vm_page_prot); if (write_access) { entry = pte_mkwrite(pte_mkdirty(entry)); } else if (mem_map[MAP_NR(page)].count > 1 && !(vma->vm_flags & VM_SHARED)) entry = pte_wrprotect(entry); put_page(page_table, entry); /* no need to invalidate: a not-present page shouldn't be cached */ return; anonymous_page: // ************************************************************** // pobranie strony z puli systemu // ************************************************************** entry = pte_wrprotect(mk_pte(ZERO_PAGE, vma->vm_page_prot)); if (write_access) { unsigned long page = __get_free_page(GFP_KERNEL); if (!page) goto sigbus; memset((void *) page, 0, PAGE_SIZE); entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot))); vma->vm_mm->rss++; tsk->min_flt++; flush_page_to_ram(page); } put_page(page_table, entry); return; sigbus: // ********************************************************** // przerwanie procesu jesli nie udalo sie wczytac/przydzielic // strony // ********************************************************** force_sig(SIGBUS, current); put_page(page_table, BAD_PAGE); /* no need to invalidate, wasn't present */ return; swap_page: // *********************************************************** // wczytanie strony z dysku // *********************************************************** do_swap_page(tsk, vma, address, page_table, entry, write_access); return; no_memory: // *********************************************************** // brak pamieci // *********************************************************** oom(tsk); is_present: return; } // *********************************************************************** // W przyszlych wersjach systemu Linux funkcje do_no_page i do_wp_page // zostana polaczone w jedna funkcje handle_mm_fault. Ma to na celu // unifikacje ich dzialania na roznych procesorach oraz uproszczenie. // *********************************************************************** /* * The above separate functions for the no-page and wp-page * cases will go away (they mostly do the same thing anyway), * and we'll instead use only a general "handle_mm_fault()". * * These routines also need to handle stuff like marking pages dirty * and/or accessed for architectures that don't do it in hardware (most * RISC architectures). The early dirtying is also good on the i386. * * There is also a hook called "update_mmu_cache()" that architectures * with external mmu caches can use to update those (ie the Sparc or * PowerPC hashed page tables that act as extended TLBs). */ static inline void handle_pte_fault(struct vm_area_struct * vma, unsigned long address, int write_access, pte_t * pte) { if (!pte_present(*pte)) { do_no_page(current, vma, address, write_access); return; } set_pte(pte, pte_mkyoung(*pte)); flush_tlb_page(vma, address); if (!write_access) return; if (pte_write(*pte)) { set_pte(pte, pte_mkdirty(*pte)); flush_tlb_page(vma, address); return; } do_wp_page(current, vma, address, write_access); } void handle_mm_fault(struct vm_area_struct * vma, unsigned long address, int write_access) { pgd_t *pgd; pmd_t *pmd; pte_t *pte; pgd = pgd_offset(vma->vm_mm, address); pmd = pmd_alloc(pgd, address); if (!pmd) goto no_memory; pte = pte_alloc(pmd, address); if (!pte) goto no_memory; handle_pte_fault(vma, address, write_access, pte); update_mmu_cache(vma, address, *pte); return; no_memory: oom(current); }