/*
 * MMU fault handling support.
 *
 * Copyright (C) 1998-2002 Hewlett-Packard Co
 *      David Mosberger-Tang <davidm@hpl.hp.com>
 */
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>

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

extern int die(char *, struct pt_regs *, long);

#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
        int ret = 0;

        if (!user_mode(regs)) {
                /* kprobe_running() needs smp_processor_id() */
                preempt_disable();
                if (kprobe_running() && kprobe_fault_handler(regs, trap))
                        ret = 1;
                preempt_enable();
        }

        return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
        return 0;
}
#endif

/*
 * Return TRUE if ADDRESS points at a page in the kernel's mapped segment
 * (inside region 5, on ia64) and that page is present.
 */
static int
mapped_kernel_page_is_present (unsigned long address)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *ptep, pte;

        pgd = pgd_offset_k(address);
        if (pgd_none(*pgd) || pgd_bad(*pgd))
                return 0;

        pud = pud_offset(pgd, address);
        if (pud_none(*pud) || pud_bad(*pud))
                return 0;

        pmd = pmd_offset(pud, address);
        if (pmd_none(*pmd) || pmd_bad(*pmd))
                return 0;

        ptep = pte_offset_kernel(pmd, address);
        if (!ptep)
                return 0;

        pte = *ptep;
        return pte_present(pte);
}

void __kprobes
ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *regs)
{
        int signal = SIGSEGV, code = SEGV_MAPERR;
        struct vm_area_struct *vma, *prev_vma;
        struct mm_struct *mm = current->mm;
        struct siginfo si;
        unsigned long mask;
        int fault;

        /* mmap_sem is performance critical.... */
        prefetchw(&mm->mmap_sem);

        /*
         * If we're in an interrupt or have no user context, we must not take the fault..
         */
        if (in_atomic() || !mm)
                goto no_context;

#ifdef CONFIG_VIRTUAL_MEM_MAP
        /*
         * If fault is in region 5 and we are in the kernel, we may already
         * have the mmap_sem (pfn_valid macro is called during mmap). There
         * is no vma for region 5 addr's anyway, so skip getting the semaphore
         * and go directly to the exception handling code.
         */

        if ((REGION_NUMBER(address) == 5) && !user_mode(regs))
                goto bad_area_no_up;
#endif

        /*
         * This is to handle the kprobes on user space access instructions
         */
        if (notify_page_fault(regs, TRAP_BRKPT))
                return;

        down_read(&mm->mmap_sem);

        vma = find_vma_prev(mm, address, &prev_vma);
        if (!vma && !prev_vma )
                goto bad_area;

        /*
         * find_vma_prev() returns vma such that address < vma->vm_end or NULL
         *
         * May find no vma, but could be that the last vm area is the
         * register backing store that needs to expand upwards, in
         * this case vma will be null, but prev_vma will ne non-null
         */
        if (( !vma && prev_vma ) || (address < vma->vm_start) )
                goto check_expansion;

  good_area:
        code = SEGV_ACCERR;

        /* OK, we've got a good vm_area for this memory area.  Check the access permissions: */

#       define VM_READ_BIT      0
#       define VM_WRITE_BIT     1
#       define VM_EXEC_BIT      2

#       if (((1 << VM_READ_BIT) != VM_READ || (1 << VM_WRITE_BIT) != VM_WRITE) \
            || (1 << VM_EXEC_BIT) != VM_EXEC)
#               error File is out of sync with <linux/mm.h>.  Please update.
#       endif

        if (((isr >> IA64_ISR_R_BIT) & 1UL) && (!(vma->vm_flags & (VM_READ | VM_WRITE))))
                goto bad_area;

        mask = (  (((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
                | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));

        if ((vma->vm_flags & mask) != mask)
                goto bad_area;

  survive:
        /*
         * If for any reason at all we couldn't handle the fault, make
         * sure we exit gracefully rather than endlessly redo the
         * fault.
         */
        fault = handle_mm_fault(mm, vma, address, (mask & VM_WRITE) ? FAULT_FLAG_WRITE : 0);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                /*
                 * We ran out of memory, or some other thing happened
                 * to us that made us unable to handle the page fault
                 * gracefully.
                 */
                if (fault & VM_FAULT_OOM) {
                        goto out_of_memory;
                } else if (fault & VM_FAULT_SIGBUS) {
                        signal = SIGBUS;
                        goto bad_area;
                }
                BUG();
        }
        if (fault & VM_FAULT_MAJOR)
                current->maj_flt++;
        else
                current->min_flt++;
        up_read(&mm->mmap_sem);
        return;

  check_expansion:
        if (!(prev_vma && (prev_vma->vm_flags & VM_GROWSUP) && (address == prev_vma->vm_end))) {
                if (!vma)
                        goto bad_area;
                if (!(vma->vm_flags & VM_GROWSDOWN))
                        goto bad_area;
                if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
                    || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
                        goto bad_area;
                if (expand_stack(vma, address))
                        goto bad_area;
        } else {
                vma = prev_vma;
                if (REGION_NUMBER(address) != REGION_NUMBER(vma->vm_start)
                    || REGION_OFFSET(address) >= RGN_MAP_LIMIT)
                        goto bad_area;
                /*
                 * Since the register backing store is accessed sequentially,
                 * we disallow growing it by more than a page at a time.
                 */
                if (address > vma->vm_end + PAGE_SIZE - sizeof(long))
                        goto bad_area;
                if (expand_upwards(vma, address))
                        goto bad_area;
        }
        goto good_area;

  bad_area:
        up_read(&mm->mmap_sem);
#ifdef CONFIG_VIRTUAL_MEM_MAP
  bad_area_no_up:
#endif
        if ((isr & IA64_ISR_SP)
            || ((isr & IA64_ISR_NA) && (isr & IA64_ISR_CODE_MASK) == IA64_ISR_CODE_LFETCH))
        {
                /*
                 * This fault was due to a speculative load or lfetch.fault, set the "ed"
                 * bit in the psr to ensure forward progress.  (Target register will get a
                 * NaT for ld.s, lfetch will be canceled.)
                 */
                ia64_psr(regs)->ed = 1;
                return;
        }
        if (user_mode(regs)) {
                si.si_signo = signal;
                si.si_errno = 0;
                si.si_code = code;
                si.si_addr = (void __user *) address;
                si.si_isr = isr;
                si.si_flags = __ISR_VALID;
                force_sig_info(signal, &si, current);
                return;
        }

  no_context:
        if ((isr & IA64_ISR_SP)
            || ((isr & IA64_ISR_NA) && (isr & IA64_ISR_CODE_MASK) == IA64_ISR_CODE_LFETCH))
        {
                /*
                 * This fault was due to a speculative load or lfetch.fault, set the "ed"
                 * bit in the psr to ensure forward progress.  (Target register will get a
                 * NaT for ld.s, lfetch will be canceled.)
                 */
                ia64_psr(regs)->ed = 1;
                return;
        }

        /*
         * Since we have no vma's for region 5, we might get here even if the address is
         * valid, due to the VHPT walker inserting a non present translation that becomes
         * stale. If that happens, the non present fault handler already purged the stale
         * translation, which fixed the problem. So, we check to see if the translation is
         * valid, and return if it is.
         */
        if (REGION_NUMBER(address) == 5 && mapped_kernel_page_is_present(address))
                return;

        if (ia64_done_with_exception(regs))
                return;

        /*
         * Oops. The kernel tried to access some bad page. We'll have to terminate things
         * with extreme prejudice.
         */
        bust_spinlocks(1);

        if (address < PAGE_SIZE)
                printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference (address %016lx)\n", address);
        else
                printk(KERN_ALERT "Unable to handle kernel paging request at "
                       "virtual address %016lx\n", address);
        if (die("Oops", regs, isr))
                regs = NULL;
        bust_spinlocks(0);
        if (regs)
                do_exit(SIGKILL);
        return;

  out_of_memory:
        up_read(&mm->mmap_sem);
        if (is_global_init(current)) {
                yield();
                down_read(&mm->mmap_sem);
                goto survive;
        }
        printk(KERN_CRIT "VM: killing process %s\n", current->comm);
        if (user_mode(regs))
                do_group_exit(SIGKILL);
        goto no_context;
}