linux 内核处理缺页异常函数：do_page_fault ，2.4.0版
关于内核地址空间如何和进程地址空间合在一起，下面函数能看出来。/* * This routine handles page faults.It determines the address, * and the problem, and then passes it off to one of the appropriate * routines. * * error_code: *bit 0 == 0 means no page found, 1 means protection fault *bit 1 == 0 means read, 1 means write *bit 2 == 0 means kernel, 1 means user-mode */asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code){struct task_struct *tsk;struct mm_struct *mm;struct vm_area_struct * vma;unsigned long address;unsigned long page;unsigned long fixup;int write;siginfo_t info;/* get the address */__asm__("movl %%cr2,%0":"=r" (address));tsk = current;/* * We fault-in kernel-space virtual memory on-demand. The * 'reference' page table is init_mm.pgd. * * NOTE! We MUST NOT take any locks for this case. We may * be in an interrupt or a critical region, and should * only copy the information from the master page table, * nothing more. */if (address >= TASK_SIZE)//关键地方就在这分叉了，如果是内核地址空间3G以上，那么···你懂的。goto vmalloc_fault;mm = tsk->mm;info.si_code = SEGV_MAPERR;/* * If we're in an interrupt or have no user * context, we must not take the fault.. */if (in_interrupt() || !mm)goto no_context;down(&mm->mmap_sem);vma = find_vma(mm, address);if (!vma)goto bad_area;if (vma->vm_start <= address)goto good_area;if (!(vma->vm_flags & VM_GROWSDOWN))goto bad_area;if (error_code & 4) {/* * accessing the stack below %esp is always a bug. * The "+ 32" is there due to some instructions (like * pusha) doing post-decrement on the stack and that * doesn't show up until later.. */if (address + 32 < regs->esp)goto bad_area;}if (expand_stack(vma, address))goto bad_area;/* * Ok, we have a good vm_area for this memory access, so * we can handle it.. */good_area:info.si_code = SEGV_ACCERR;write = 0;switch (error_code & 3) {default:/* 3: write, present */#ifdef TEST_VERIFY_AREAif (regs->cs == KERNEL_CS)printk("WP fault at %08lx\n", regs->eip);#endif/* fall through */case 2:/* write, not present */if (!(vma->vm_flags & VM_WRITE))goto bad_area;write++;break;case 1:/* read, present */goto bad_area;case 0:/* read, not present */if (!(vma->vm_flags & (VM_READ | VM_EXEC)))goto bad_area;}/* * If for any reason at all we couldn't handle the fault, * make sure we exit gracefully rather than endlessly redo * the fault. */switch (handle_mm_fault(mm, vma, address, write)) {case 1:tsk->min_flt++;break;case 2:tsk->maj_flt++;break;case 0:goto do_sigbus;default:goto out_of_memory;}/* * Did it hit the DOS screen memory VA from vm86 mode? */if (regs->eflags & VM_MASK) {unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;if (bit < 32)tsk->thread.screen_bitmap |= 1 << bit;}up(&mm->mmap_sem);return;/* * Something tried to access memory that isn't in our memory map.. * Fix it, but check if it's kernel or user first.. */bad_area:up(&mm->mmap_sem);bad_area_nosemaphore:/* User mode accesses just cause a SIGSEGV */if (error_code & 4) {tsk->thread.cr2 = address;tsk->thread.error_code = error_code;tsk->thread.trap_no = 14;info.si_signo = SIGSEGV;info.si_errno = 0;/* info.si_code has been set above */info.si_addr = (void *)address;force_sig_info(SIGSEGV, &info, tsk);return;}/* * Pentium F0 0F C7 C8 bug workaround. */if (boot_cpu_data.f00f_bug) {unsigned long nr;nr = (address - idt) >> 3;if (nr == 6) {do_invalid_op(regs, 0);return;}}no_context:/* Are we prepared to handle this kernel fault?*/if ((fixup = search_exception_table(regs->eip)) != 0) {regs->eip = fixup;return;}/* * Oops. The kernel tried to access some bad page. We'll have to * terminate things with extreme prejudice. */bust_spinlocks();if (address < PAGE_SIZE)printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");elseprintk(KERN_ALERT "Unable to handle kernel paging request");printk(" at virtual address %08lx\n",address);printk(" printing eip:\n");printk("%08lx\n", regs->eip);asm("movl %%cr3,%0":"=r" (page));page = ((unsigned long *) __va(page));printk(KERN_ALERT "*pde = %08lx\n", page);if (page & 1) {page &= PAGE_MASK;address &= 0x003ff000;page = ((unsigned long *) __va(page));printk(KERN_ALERT "*pte = %08lx\n", page);}die("Oops", regs, error_code);do_exit(SIGKILL);/* * We ran out of memory, or some other thing happened to us that made * us unable to handle the page fault gracefully. */out_of_memory:up(&mm->mmap_sem);printk("VM: killing process %s\n", tsk->comm);if (error_code & 4)do_exit(SIGKILL);goto no_context;do_sigbus:up(&mm->mmap_sem);/* * Send a sigbus, regardless of whether we were in kernel * or user mode. */tsk->thread.cr2 = address;tsk->thread.error_code = error_code;tsk->thread.trap_no = 14;info.si_code = SIGBUS;info.si_errno = 0;info.si_code = BUS_ADRERR;info.si_addr = (void *)address;force_sig_info(SIGBUS, &info, tsk);/* Kernel mode? Handle exceptions or die */if (!(error_code & 4))goto no_context;return;vmalloc_fault://下面就是如何处理内核地址空间的问题了。这里实现内核全局页目录表和进程页目录表同步{/* * Synchronize this task's top level page-table * with the 'reference' page table. */int offset = __pgd_offset(address);pgd_t *pgd, *pgd_k;pmd_t *pmd, *pmd_k;pgd = tsk->active_mm->pgd + offset;pgd_k = init_mm.pgd + offset;if (!pgd_present(*pgd)) {if (!pgd_present(*pgd_k))goto bad_area_nosemaphore;set_pgd(pgd, *pgd_k);return;}pmd = pmd_offset(pgd, address);pmd_k = pmd_offset(pgd_k, address);if (pmd_present(*pmd) || !pmd_present(*pmd_k))goto bad_area_nosemaphore;set_pmd(pmd, *pmd_k);return;}}
页:
[1]