/*
 *  linux/arch/cris/mm/fault.c
 *
 *  Copyright (C) 2000, 2001  Axis Communications AB
 *
 *  Authors:  Bjorn Wesen 
 * 
 *  $Log: fault.c,v $
 *  Revision 1.11  2004/05/14 07:58:05  starvik
 *  Merge of changes from 2.4
 *
 *  Revision 1.10  2003/10/27 14:51:24  starvik
 *  Removed debugcode
 *
 *  Revision 1.9  2003/10/27 14:50:42  starvik
 *  Changed do_page_fault signature
 *
 *  Revision 1.8  2003/07/04 13:02:48  tobiasa
 *  Moved code snippet from arch/cris/mm/fault.c that searches for fixup code
 *  to seperate function in arch-specific files.
 *
 *  Revision 1.7  2003/01/22 06:48:38  starvik
 *  Fixed warnings issued by GCC 3.2.1
 *
 *  Revision 1.6  2003/01/09 14:42:52  starvik
 *  Merge of Linux 2.5.55
 *
 *  Revision 1.5  2002/12/11 14:44:48  starvik
 *  Extracted v10 (ETRAX 100LX) specific stuff to arch/cris/arch-v10/mm
 *
 *  Revision 1.4  2002/11/13 15:10:28  starvik
 *  pte_offset has been renamed to pte_offset_kernel
 *
 *  Revision 1.3  2002/11/05 06:45:13  starvik
 *  Merge of Linux 2.5.45
 *
 *  Revision 1.2  2001/12/18 13:35:22  bjornw
 *  Applied the 2.4.13->2.4.16 CRIS patch to 2.5.1 (is a copy of 2.4.15).
 *
 *  Revision 1.20  2001/11/22 13:34:06  bjornw
 *  * Bug workaround (LX TR89): force a rerun of the whole of an interrupted
 *    unaligned write, because the second half of the write will be corrupted
 *    otherwise. Affected unaligned writes spanning not-yet mapped pages.
 *  * Optimization: use the wr_rd bit in R_MMU_CAUSE to know whether a miss
 *    was due to a read or a write (before we didn't know this until the next
 *    restart of the interrupted instruction, thus wasting one fault-irq)
 *
 *  Revision 1.19  2001/11/12 19:02:10  pkj
 *  Fixed compiler warnings.
 *
 *  Revision 1.18  2001/07/18 22:14:32  bjornw
 *  Enable interrupts in the bulk of do_page_fault
 *
 *  Revision 1.17  2001/07/18 13:07:23  bjornw
 *  * Detect non-existant PTE's in vmalloc pmd synchronization
 *  * Remove comment about fast-paths for VMALLOC_START etc, because all that
 *    was totally bogus anyway it turned out :)
 *  * Fix detection of vmalloc-area synchronization
 *  * Add some comments
 *
 *  Revision 1.16  2001/06/13 00:06:08  bjornw
 *  current_pgd should be volatile
 *
 *  Revision 1.15  2001/06/13 00:02:23  bjornw
 *  Use a separate variable to store the current pgd to avoid races in schedule
 *
 *  Revision 1.14  2001/05/16 17:41:07  hp
 *  Last comment tweak further tweaked.
 *
 *  Revision 1.13  2001/05/15 00:58:44  hp
 *  Expand a bit on the comment why we compare address >= TASK_SIZE rather
 *  than >= VMALLOC_START.
 *
 *  Revision 1.12  2001/04/04 10:51:14  bjornw
 *  mmap_sem is grabbed for reading
 *
 *  Revision 1.11  2001/03/23 07:36:07  starvik
 *  Corrected according to review remarks
 *
 *  Revision 1.10  2001/03/21 16:10:11  bjornw
 *  CRIS_FRAME_FIXUP not needed anymore, use FRAME_NORMAL
 *
 *  Revision 1.9  2001/03/05 13:22:20  bjornw
 *  Spell-fix and fix in vmalloc_fault handling
 *
 *  Revision 1.8  2000/11/22 14:45:31  bjornw
 *  * 2.4.0-test10 removed the set_pgdir instantaneous kernel global mapping
 *    into all processes. Instead we fill in the missing PTE entries on demand.
 *
 *  Revision 1.7  2000/11/21 16:39:09  bjornw
 *  fixup switches frametype
 *
 *  Revision 1.6  2000/11/17 16:54:08  bjornw
 *  More detailed siginfo reporting
 *
 *
 */

#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 */

volatile pgd_t *current_pgd;

/*
 * 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;

        D(printk("Page fault for %X at %X, prot %d write %d\n",
                 address, regs->erp, 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;

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

        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) {
                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.
         */

        switch (handle_mm_fault(mm, vma, address, writeaccess)) {
        case 1:
                tsk->min_flt++;
                break;
        case 2:
                tsk->maj_flt++;
                break;
        case 0:
                goto do_sigbus;
        default:
                goto out_of_memory;
        }

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

        die_if_kernel("Oops", regs, (writeaccess << 1) | protection);

        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;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                pgd = (pgd_t *)current_pgd + 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.
                 */

                pmd = pmd_offset(pgd, address);
                pmd_k = pmd_offset(pgd_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;
        }
}