/*
 *  linux/arch/cris/mm/fault.c
 *
 *  Copyright (C) 2000-2006  Axis Communications AB
 *
 *  Authors:  Bjorn Wesen
 *
 */

#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <asm/uaccess.h>

extern int find_fixup_code(struct pt_regs *);
extern void die_if_kernel(const char *, struct pt_regs *, long);

/* debug of low-level TLB reload */
#undef DEBUG

#ifdef DEBUG
#define D(x) x
#else
#define D(x)
#endif

/* debug of higher-level faults */
#define DPG(x)

/* current active page directory */

DEFINE_PER_CPU(pgd_t *, current_pgd);
unsigned long cris_signal_return_page;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Notice that the address we're given is aligned to the page the fault
 * occurred in, since we only get the PFN in R_MMU_CAUSE not the complete
 * address.
 *
 * error_code:
 *      bit 0 == 0 means no page found, 1 means protection fault
 *      bit 1 == 0 means read, 1 means write
 *
 * If this routine detects a bad access, it returns 1, otherwise it
 * returns 0.
 */

asmlinkage void
do_page_fault(unsigned long address, struct pt_regs *regs,
              int protection, int writeaccess)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct * vma;
        siginfo_t info;
        int fault;

        D(printk(KERN_DEBUG
                 "Page fault for %lX on %X at %lX, prot %d write %d\n",
                 address, smp_processor_id(), instruction_pointer(regs),
                 protection, writeaccess));

        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.
         *
         * NOTE2: This is done so that, when updating the vmalloc
         * mappings we don't have to walk all processes pgdirs and
         * add the high mappings all at once. Instead we do it as they
         * are used. However vmalloc'ed page entries have the PAGE_GLOBAL
         * bit set so sometimes the TLB can use a lingering entry.
         *
         * This verifies that the fault happens in kernel space
         * and that the fault was not a protection error (error_code & 1).
         */

        if (address >= VMALLOC_START &&
            !protection &&
            !user_mode(regs))
                goto vmalloc_fault;

        /* When stack execution is not allowed we store the signal
         * trampolines in the reserved cris_signal_return_page.
         * Handle this in the exact same way as vmalloc (we know
         * that the mapping is there and is valid so no need to
         * call handle_mm_fault).
         */
        if (cris_signal_return_page &&
            address == cris_signal_return_page &&
            !protection && user_mode(regs))
                goto vmalloc_fault;

        /* we can and should enable interrupts at this point */
        local_irq_enable();

        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_read(&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 (user_mode(regs)) {
                /*
                 * accessing the stack below usp is always a bug.
                 * we get page-aligned addresses so we can only check
                 * if we're within a page from usp, but that might be
                 * enough to catch brutal errors at least.
                 */
                if (address + PAGE_SIZE < rdusp())
                        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;

        /* first do some preliminary protection checks */

        if (writeaccess == 2){
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
        } else if (writeaccess == 1) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
        } else {
                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.
         */

        fault = handle_mm_fault(mm, vma, address, (writeaccess & 1) ? FAULT_FLAG_WRITE : 0);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
                        goto out_of_memory;
                else if (fault & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
        }
        if (fault & VM_FAULT_MAJOR)
                tsk->maj_flt++;
        else
                tsk->min_flt++;

        up_read(&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_read(&mm->mmap_sem);

 bad_area_nosemaphore:
        DPG(show_registers(regs));

        /* User mode accesses just cause a SIGSEGV */

        if (user_mode(regs)) {
                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);
                printk(KERN_NOTICE "%s (pid %d) segfaults for page "
                       "address %08lx at pc %08lx\n",
                       tsk->comm, tsk->pid, address, instruction_pointer(regs));
                return;
        }

 no_context:

        /* Are we prepared to handle this kernel fault?
         *
         * (The kernel has valid exception-points in the source
         *  when it acesses user-memory. When it fails in one
         *  of those points, we find it in a table and do a jump
         *  to some fixup code that loads an appropriate error
         *  code)
         */

        if (find_fixup_code(regs))
                return;

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

        if (!oops_in_progress) {
                oops_in_progress = 1;
                if ((unsigned long) (address) < PAGE_SIZE)
                        printk(KERN_ALERT "Unable to handle kernel NULL "
                                "pointer dereference");
                else
                        printk(KERN_ALERT "Unable to handle kernel access"
                                " at virtual address %08lx\n", address);

                die_if_kernel("Oops", regs, (writeaccess << 1) | protection);
                oops_in_progress = 0;
        }

        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_read(&mm->mmap_sem);
        printk("VM: killing process %s\n", tsk->comm);
        if (user_mode(regs))
                do_exit(SIGKILL);
        goto no_context;

 do_sigbus:
        up_read(&mm->mmap_sem);

        /*
         * Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        info.si_signo = 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 (!user_mode(regs))
                goto no_context;
        return;

vmalloc_fault:
        {
                /*
                 * Synchronize this task's top level page-table
                 * with the 'reference' page table.
                 *
                 * Use current_pgd instead of tsk->active_mm->pgd
                 * since the latter might be unavailable if this
                 * code is executed in a misfortunately run irq
                 * (like inside schedule() between switch_mm and
                 *  switch_to...).
                 */

                int offset = pgd_index(address);
                pgd_t *pgd, *pgd_k;
                pud_t *pud, *pud_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                pgd = (pgd_t *)per_cpu(current_pgd, smp_processor_id()) + offset;
                pgd_k = init_mm.pgd + offset;

                /* Since we're two-level, we don't need to do both
                 * set_pgd and set_pmd (they do the same thing). If
                 * we go three-level at some point, do the right thing
                 * with pgd_present and set_pgd here.
                 *
                 * Also, since the vmalloc area is global, we don't
                 * need to copy individual PTE's, it is enough to
                 * copy the pgd pointer into the pte page of the
                 * root task. If that is there, we'll find our pte if
                 * it exists.
                 */

                pud = pud_offset(pgd, address);
                pud_k = pud_offset(pgd_k, address);
                if (!pud_present(*pud_k))
                        goto no_context;

                pmd = pmd_offset(pud, address);
                pmd_k = pmd_offset(pud_k, address);

                if (!pmd_present(*pmd_k))
                        goto bad_area_nosemaphore;

                set_pmd(pmd, *pmd_k);

                /* Make sure the actual PTE exists as well to
                 * catch kernel vmalloc-area accesses to non-mapped
                 * addresses. If we don't do this, this will just
                 * silently loop forever.
                 */

                pte_k = pte_offset_kernel(pmd_k, address);
                if (!pte_present(*pte_k))
                        goto no_context;

                return;
        }
}

/* Find fixup code. */
int
find_fixup_code(struct pt_regs *regs)
{
        const struct exception_table_entry *fixup;

        if ((fixup = search_exception_tables(instruction_pointer(regs))) != 0) {
                /* Adjust the instruction pointer in the stackframe. */
                instruction_pointer(regs) = fixup->fixup;
                arch_fixup(regs);
                return 1;
        }

        return 0;
}