/*
 *  linux/arch/i386/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#include <linux/signal.h>
#include <linux/sched.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/smp.h>
#include <linux/smp_lock.h>
#include <linux/interrupt.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/hardirq.h>

extern void die(const char *,struct pt_regs *,long);

/*
 * Ugly, ugly, but the goto's result in better assembly..
 */
int __verify_write(const void * addr, unsigned long size)
{
	struct vm_area_struct * vma;
	unsigned long start = (unsigned long) addr;

	if (!size)
		return 1;

	vma = find_vma(current->mm, start);
	if (!vma)
		goto bad_area;
	if (vma->vm_start > start)
		goto check_stack;

good_area:
	if (!(vma->vm_flags & VM_WRITE))
		goto bad_area;
	size--;
	size += start & ~PAGE_MASK;
	size >>= PAGE_SHIFT;
	start &= PAGE_MASK;

	for (;;) {
	survive:
		{
			int fault = handle_mm_fault(current,vma, start, 1);
			if (!fault)
				goto do_sigbus;
			if (fault < 0)
				goto out_of_memory;
		}
		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 1;

check_stack:
	if (!(vma->vm_flags & VM_GROWSDOWN))
		goto bad_area;
	if (expand_stack(vma, start) == 0)
		goto good_area;

bad_area:
	return 0;

do_sigbus:
	force_sig(SIGBUS, current);
	goto bad_area;

out_of_memory:
	if (current->pid == 1)
	{
		current->policy |= SCHED_YIELD;
		schedule();
		goto survive;
	}
	goto bad_area;
}

asmlinkage void do_invalid_op(struct pt_regs *, unsigned long);
extern unsigned long idt;

/*
 * 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;

	/* get the address */
	__asm__("movl %%cr2,%0":"=r" (address));

	tsk = current;
	mm = tsk->mm;

	/*
	 * If we're in an interrupt or have no user
	 * context, we must not take the fault..
	 */
	if (in_interrupt() || mm == &init_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:
	write = 0;
	switch (error_code & 3) {
		default:	/* 3: write, present */
#ifdef TEST_VERIFY_AREA
			if (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.
	 */
survive:
	{
		int fault = handle_mm_fault(tsk, vma, address, write);
		if (!fault)
			goto do_sigbus;
		if (fault < 0)
			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->tss.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);

	/* User mode accesses just cause a SIGSEGV */
	if (error_code & 4) {
		tsk->tss.cr2 = address;
		tsk->tss.error_code = error_code;
		tsk->tss.trap_no = 14;
		force_sig(SIGSEGV, 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.
 *
 * First we check if it was the bootup rw-test, though..
 */
	if (boot_cpu_data.wp_works_ok < 0 &&
	    address == PAGE_OFFSET && (error_code & 1)) {
		boot_cpu_data.wp_works_ok = 1;
		pg0[0] = pte_val(mk_pte(PAGE_OFFSET, PAGE_KERNEL));
		local_flush_tlb();
		/*
		 * Beware: Black magic here. The printk is needed here to flush
		 * CPU state on certain buggy processors.
		 */
		printk("Ok");
		return;
	}

	if (address < PAGE_SIZE)
		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
	else
		printk(KERN_ALERT "Unable to handle kernel paging request");
	printk(" at virtual address %08lx\n",address);
	__asm__("movl %%cr3,%0" : "=r" (page));
	printk(KERN_ALERT "current->tss.cr3 = %08lx, %%cr3 = %08lx\n",
		tsk->tss.cr3, page);
	page = ((unsigned long *) __va(page))[address >> 22];
	printk(KERN_ALERT "*pde = %08lx\n", page);
	if (page & 1) {
		page &= PAGE_MASK;
		address &= 0x003ff000;
		page = ((unsigned long *) __va(page))[address >> PAGE_SHIFT];
		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:
	if (tsk->pid == 1)
	{
		tsk->policy |= SCHED_YIELD;
		schedule();
		goto survive;
	}
	up(&mm->mmap_sem);
	if (error_code & 4)
	{
		if (tsk->oom_kill_try++ > 10 ||
		    !((regs->eflags >> 12) & 3))
		{
			printk("VM: killing process %s\n", tsk->comm);
			do_exit(SIGKILL);
		}
		else
		{
			/*
			 * The task is running with privilegies and so we
			 * trust it and we give it a chance to die gracefully.
			 */
			printk("VM: terminating process %s\n", tsk->comm);
			force_sig(SIGTERM, current);
			if (tsk->oom_kill_try > 1)
			{
				tsk->policy |= SCHED_YIELD;
				schedule();
			}
			return;
		}
	}
	goto no_context;

do_sigbus:
	up(&mm->mmap_sem);

	/*
	 * Send a sigbus, regardless of whether we were in kernel
	 * or user mode.
	 */
	tsk->tss.cr2 = address;
	tsk->tss.error_code = error_code;
	tsk->tss.trap_no = 14;
	force_sig(SIGBUS, tsk);

	/* Kernel mode? Handle exceptions or die */
	if (!(error_code & 4))
		goto no_context;
}
