/*
 *  linux/arch/cris/mm/fault.c
 *
 *  Copyright (C) 2000, 2001  Axis Communications AB
 *
 *  Authors:  Bjorn Wesen 
 * 
 *  $Log: fault.c,v $
 *  Revision 1.23  2003/10/16 05:32:32  starvik
 *  Only read TLB_SELECT if DEBUG
 *
 *  Revision 1.22  2003/07/07 09:07:04  johana
 *  Added special CONFIG_ETRAX_DEBUG_INTERRUPT handling here
 *  to deal with a di in entry.S
 *
 *  Revision 1.21  2002/05/28 14:24:56  bjornw
 *  Corrected typo
 *
 *  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/config.h>
#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/interrupt.h>

#include <asm/system.h>
#include <asm/segment.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/svinto.h>

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

asmlinkage void do_invalid_op (struct pt_regs *, unsigned long);
asmlinkage void do_page_fault(unsigned long address, struct pt_regs *regs,
                              int error_code);

/* 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;

/* fast TLB-fill fault handler
 * this is called from entry.S with interrupts disabled
 */

void
handle_mmu_bus_fault(struct pt_regs *regs)
{
        int cause;
#ifdef DEBUG
        int select;
        int index;
        int page_id;
        int acc, inv;
#endif
        int miss, we, writeac;
        pmd_t *pmd;
        pte_t pte;
        int errcode;
        unsigned long address;

#ifdef CONFIG_ETRAX_DEBUG_INTERRUPT /* The di is actually in entry.S */
        log_int(rdpc(), regs->dccr, 0);
#endif
        cause = *R_MMU_CAUSE;

        address = cause & PAGE_MASK; /* get faulting address */

#ifdef DEBUG
        select = *R_TLB_SELECT;
        page_id = IO_EXTRACT(R_MMU_CAUSE,  page_id,   cause);
        acc     = IO_EXTRACT(R_MMU_CAUSE,  acc_excp,  cause);
        inv     = IO_EXTRACT(R_MMU_CAUSE,  inv_excp,  cause);  
        index   = IO_EXTRACT(R_TLB_SELECT, index,     select);
#endif
        miss    = IO_EXTRACT(R_MMU_CAUSE,  miss_excp, cause);
        we      = IO_EXTRACT(R_MMU_CAUSE,  we_excp,   cause);
        writeac = IO_EXTRACT(R_MMU_CAUSE,  wr_rd,     cause);

        /* ETRAX 100LX TR89 bugfix: if the second half of an unaligned
         * write causes a MMU-fault, it will not be restarted correctly.
         * This could happen if a write crosses a page-boundary and the
         * second page is not yet COW'ed or even loaded. The workaround
         * is to clear the unaligned bit in the CPU status record, so 
         * that the CPU will rerun both the first and second halves of
         * the instruction. This will not have any sideeffects unless
         * the first half goes to any device or memory that can't be
         * written twice, and which is mapped through the MMU.
         *
         * We only need to do this for writes.
         */

        if(writeac)
                regs->csrinstr &= ~(1 << 5);
        
        /* Set errcode's R/W flag according to the mode which caused the
         * fault
         */

        errcode = writeac << 1;

        D(printk("bus_fault from IRP 0x%lx: addr 0x%lx, miss %d, inv %d, we %d, acc %d, dx %d pid %d\n",
                 regs->irp, address, miss, inv, we, acc, index, page_id));

        /* for a miss, we need to reload the TLB entry */

        if (miss) {
                /* see if the pte exists at all
                 * refer through current_pgd, dont use mm->pgd
                 */

                pmd = (pmd_t *)(current_pgd + pgd_index(address));
                if (pmd_none(*pmd))
                        goto dofault;
                if (pmd_bad(*pmd)) {
                        printk("bad pgdir entry 0x%lx at 0x%p\n", *(unsigned long*)pmd, pmd);
                        pmd_clear(pmd);
                        return;
                }
                pte = *pte_offset(pmd, address);
                if (!pte_present(pte))
                        goto dofault;

#ifdef DEBUG
                printk(" found pte %lx pg %p ", pte_val(pte), pte_page(pte));
                if (pte_val(pte) & _PAGE_SILENT_WRITE)
                        printk("Silent-W ");
                if (pte_val(pte) & _PAGE_KERNEL)
                        printk("Kernel ");
                if (pte_val(pte) & _PAGE_SILENT_READ)
                        printk("Silent-R ");
                if (pte_val(pte) & _PAGE_GLOBAL)
                        printk("Global ");
                if (pte_val(pte) & _PAGE_PRESENT)
                        printk("Present ");
                if (pte_val(pte) & _PAGE_ACCESSED)
                        printk("Accessed ");
                if (pte_val(pte) & _PAGE_MODIFIED)
                        printk("Modified ");
                if (pte_val(pte) & _PAGE_READ)
                        printk("Readable ");
                if (pte_val(pte) & _PAGE_WRITE)
                        printk("Writeable ");
                printk("\n");
#endif

                /* load up the chosen TLB entry
                 * this assumes the pte format is the same as the TLB_LO layout.
                 *
                 * the write to R_TLB_LO also writes the vpn and page_id fields from
                 * R_MMU_CAUSE, which we in this case obviously want to keep
                 */

                *R_TLB_LO = pte_val(pte);

                return;
        } 

        errcode = 1 | (we << 1);

 dofault:
        /* leave it to the MM system fault handler below */
        D(printk("do_page_fault %lx errcode %d\n", address, errcode));
        do_page_fault(address, regs, errcode);
}

/*
 * 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 error_code)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct * vma;
        int writeaccess;
        unsigned long fixup;
        siginfo_t info;

        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 &&
            !(error_code & 1) &&
            !user_mode(regs))
                goto vmalloc_fault;

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

        mm = tsk->mm;
        writeaccess = error_code & 2;
        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 ((fixup = search_exception_table(regs->irp)) != 0) {
                /* Adjust the instruction pointer in the stackframe */

                regs->irp = fixup;

                /* We do not want to return by restoring the CPU-state
                 * anymore, so switch frame-types (see ptrace.h)
                 */

                regs->frametype = CRIS_FRAME_NORMAL;

                D(printk("doing fixup to 0x%lx\n", fixup));
                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, 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_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(pmd_k, address);
                if (!pte_present(*pte_k))
                        goto no_context;

                return;
        }
}