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);
}