/*
 * linux/arch/unicore32/mm/fault.c
 *
 * Code specific to PKUnity SoC and UniCore ISA
 *
 * Copyright (C) 2001-2010 GUAN Xue-tao
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/extable.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/page-flags.h>
#include <linux/sched/signal.h>
#include <linux/io.h>

#include <asm/pgtable.h>
#include <asm/tlbflush.h>

/*
 * Fault status register encodings.  We steal bit 31 for our own purposes.
 */
#define FSR_LNX_PF              (1 << 31)

static inline int fsr_fs(unsigned int fsr)
{
        /* xyabcde will be abcde+xy */
        return (fsr & 31) + ((fsr & (3 << 5)) >> 5);
}

/*
 * This is useful to dump out the page tables associated with
 * 'addr' in mm 'mm'.
 */
void show_pte(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;

        if (!mm)
                mm = &init_mm;

        printk(KERN_ALERT "pgd = %p\n", mm->pgd);
        pgd = pgd_offset(mm, addr);
        printk(KERN_ALERT "[%08lx] *pgd=%08lx", addr, pgd_val(*pgd));

        do {
                pmd_t *pmd;
                pte_t *pte;

                if (pgd_none(*pgd))
                        break;

                if (pgd_bad(*pgd)) {
                        printk("(bad)");
                        break;
                }

                pmd = pmd_offset((pud_t *) pgd, addr);
                if (PTRS_PER_PMD != 1)
                        printk(", *pmd=%08lx", pmd_val(*pmd));

                if (pmd_none(*pmd))
                        break;

                if (pmd_bad(*pmd)) {
                        printk("(bad)");
                        break;
                }

                /* We must not map this if we have highmem enabled */
                if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
                        break;

                pte = pte_offset_map(pmd, addr);
                printk(", *pte=%08lx", pte_val(*pte));
                pte_unmap(pte);
        } while (0);

        printk("\n");
}

/*
 * Oops.  The kernel tried to access some page that wasn't present.
 */
static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr,
                unsigned int fsr, struct pt_regs *regs)
{
        /*
         * Are we prepared to handle this kernel fault?
         */
        if (fixup_exception(regs))
                return;

        /*
         * No handler, we'll have to terminate things with extreme prejudice.
         */
        bust_spinlocks(1);
        printk(KERN_ALERT
               "Unable to handle kernel %s at virtual address %08lx\n",
               (addr < PAGE_SIZE) ? "NULL pointer dereference" :
               "paging request", addr);

        show_pte(mm, addr);
        die("Oops", regs, fsr);
        bust_spinlocks(0);
        do_exit(SIGKILL);
}

/*
 * Something tried to access memory that isn't in our memory map..
 * User mode accesses just cause a SIGSEGV
 */
static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
                unsigned int fsr, unsigned int sig, int code,
                struct pt_regs *regs)
{
        struct siginfo si;

        tsk->thread.address = addr;
        tsk->thread.error_code = fsr;
        tsk->thread.trap_no = 14;
        clear_siginfo(&si);
        si.si_signo = sig;
        si.si_errno = 0;
        si.si_code = code;
        si.si_addr = (void __user *)addr;
        force_sig_info(sig, &si, tsk);
}

void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->active_mm;

        /*
         * If we are in kernel mode at this point, we
         * have no context to handle this fault with.
         */
        if (user_mode(regs))
                __do_user_fault(tsk, addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
        else
                __do_kernel_fault(mm, addr, fsr, regs);
}

#define VM_FAULT_BADMAP         0x010000
#define VM_FAULT_BADACCESS      0x020000

/*
 * Check that the permissions on the VMA allow for the fault which occurred.
 * If we encountered a write fault, we must have write permission, otherwise
 * we allow any permission.
 */
static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma)
{
        unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;

        if (!(fsr ^ 0x12))      /* write? */
                mask = VM_WRITE;
        if (fsr & FSR_LNX_PF)
                mask = VM_EXEC;

        return vma->vm_flags & mask ? false : true;
}

static vm_fault_t __do_pf(struct mm_struct *mm, unsigned long addr,
                unsigned int fsr, unsigned int flags, struct task_struct *tsk)
{
        struct vm_area_struct *vma;
        vm_fault_t fault;

        vma = find_vma(mm, addr);
        fault = VM_FAULT_BADMAP;
        if (unlikely(!vma))
                goto out;
        if (unlikely(vma->vm_start > addr))
                goto check_stack;

        /*
         * Ok, we have a good vm_area for this
         * memory access, so we can handle it.
         */
good_area:
        if (access_error(fsr, vma)) {
                fault = VM_FAULT_BADACCESS;
                goto out;
        }

        /*
         * 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(vma, addr & PAGE_MASK, flags);
        return fault;

check_stack:
        if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
                goto good_area;
out:
        return fault;
}

static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        int sig, code;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        tsk = current;
        mm = tsk->mm;

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

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
        if (!(fsr ^ 0x12))
                flags |= FAULT_FLAG_WRITE;

        /*
         * As per x86, we may deadlock here.  However, since the kernel only
         * validly references user space from well defined areas of the code,
         * we can bug out early if this is from code which shouldn't.
         */
        if (!down_read_trylock(&mm->mmap_sem)) {
                if (!user_mode(regs)
                    && !search_exception_tables(regs->UCreg_pc))
                        goto no_context;
retry:
                down_read(&mm->mmap_sem);
        } else {
                /*
                 * The above down_read_trylock() might have succeeded in
                 * which case, we'll have missed the might_sleep() from
                 * down_read()
                 */
                might_sleep();
#ifdef CONFIG_DEBUG_VM
                if (!user_mode(regs) &&
                    !search_exception_tables(regs->UCreg_pc))
                        goto no_context;
#endif
        }

        fault = __do_pf(mm, addr, fsr, flags, tsk);

        /* If we need to retry but a fatal signal is pending, handle the
         * signal first. We do not need to release the mmap_sem because
         * it would already be released in __lock_page_or_retry in
         * mm/filemap.c. */
        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
                return 0;

        if (!(fault & VM_FAULT_ERROR) && (flags & FAULT_FLAG_ALLOW_RETRY)) {
                if (fault & VM_FAULT_MAJOR)
                        tsk->maj_flt++;
                else
                        tsk->min_flt++;
                if (fault & VM_FAULT_RETRY) {
                        /* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
                        * of starvation. */
                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
                        goto retry;
                }
        }

        up_read(&mm->mmap_sem);

        /*
         * Handle the "normal" case first - VM_FAULT_MAJOR
         */
        if (likely(!(fault &
               (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
                return 0;

        /*
         * If we are in kernel mode at this point, we
         * have no context to handle this fault with.
         */
        if (!user_mode(regs))
                goto no_context;

        if (fault & VM_FAULT_OOM) {
                /*
                 * We ran out of memory, call the OOM killer, and return to
                 * userspace (which will retry the fault, or kill us if we
                 * got oom-killed)
                 */
                pagefault_out_of_memory();
                return 0;
        }

        if (fault & VM_FAULT_SIGBUS) {
                /*
                 * We had some memory, but were unable to
                 * successfully fix up this page fault.
                 */
                sig = SIGBUS;
                code = BUS_ADRERR;
        } else {
                /*
                 * Something tried to access memory that
                 * isn't in our memory map..
                 */
                sig = SIGSEGV;
                code = fault == VM_FAULT_BADACCESS ? SEGV_ACCERR : SEGV_MAPERR;
        }

        __do_user_fault(tsk, addr, fsr, sig, code, regs);
        return 0;

no_context:
        __do_kernel_fault(mm, addr, fsr, regs);
        return 0;
}

/*
 * First Level Translation Fault Handler
 *
 * We enter here because the first level page table doesn't contain
 * a valid entry for the address.
 *
 * If the address is in kernel space (>= TASK_SIZE), then we are
 * probably faulting in the vmalloc() area.
 *
 * If the init_task's first level page tables contains the relevant
 * entry, we copy the it to this task.  If not, we send the process
 * a signal, fixup the exception, or oops the kernel.
 *
 * 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.
 */
static int do_ifault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        unsigned int index;
        pgd_t *pgd, *pgd_k;
        pmd_t *pmd, *pmd_k;

        if (addr < TASK_SIZE)
                return do_pf(addr, fsr, regs);

        if (user_mode(regs))
                goto bad_area;

        index = pgd_index(addr);

        pgd = cpu_get_pgd() + index;
        pgd_k = init_mm.pgd + index;

        if (pgd_none(*pgd_k))
                goto bad_area;

        pmd_k = pmd_offset((pud_t *) pgd_k, addr);
        pmd = pmd_offset((pud_t *) pgd, addr);

        if (pmd_none(*pmd_k))
                goto bad_area;

        set_pmd(pmd, *pmd_k);
        flush_pmd_entry(pmd);
        return 0;

bad_area:
        do_bad_area(addr, fsr, regs);
        return 0;
}

/*
 * This abort handler always returns "fault".
 */
static int do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        return 1;
}

static int do_good(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
        unsigned int res1, res2;

        printk("dabt exception but no error!\n");

        __asm__ __volatile__(
                        "mff %0,f0\n"
                        "mff %1,f1\n"
                        : "=r"(res1), "=r"(res2)
                        :
                        : "memory");

        printk(KERN_EMERG "r0 :%08x  r1 :%08x\n", res1, res2);
        panic("shut up\n");
        return 0;
}

static struct fsr_info {
        int (*fn) (unsigned long addr, unsigned int fsr, struct pt_regs *regs);
        int sig;
        int code;
        const char *name;
} fsr_info[] = {
        /*
         * The following are the standard Unicore-I and UniCore-II aborts.
         */
        { do_good,      SIGBUS,  0,             "no error"              },
        { do_bad,       SIGBUS,  BUS_ADRALN,    "alignment exception"   },
        { do_bad,       SIGBUS,  BUS_OBJERR,    "external exception"    },
        { do_bad,       SIGBUS,  0,             "burst operation"       },
        { do_bad,       SIGBUS,  0,             "unknown 00100"         },
        { do_ifault,    SIGSEGV, SEGV_MAPERR,   "2nd level pt non-exist"},
        { do_bad,       SIGBUS,  0,             "2nd lvl large pt non-exist" },
        { do_bad,       SIGBUS,  0,             "invalid pte"           },
        { do_pf,        SIGSEGV, SEGV_MAPERR,   "page miss"             },
        { do_bad,       SIGBUS,  0,             "middle page miss"      },
        { do_bad,       SIGBUS,  0,             "large page miss"       },
        { do_pf,        SIGSEGV, SEGV_MAPERR,   "super page (section) miss" },
        { do_bad,       SIGBUS,  0,             "unknown 01100"         },
        { do_bad,       SIGBUS,  0,             "unknown 01101"         },
        { do_bad,       SIGBUS,  0,             "unknown 01110"         },
        { do_bad,       SIGBUS,  0,             "unknown 01111"         },
        { do_bad,       SIGBUS,  0,             "addr: up 3G or IO"     },
        { do_pf,        SIGSEGV, SEGV_ACCERR,   "read unreadable addr"  },
        { do_pf,        SIGSEGV, SEGV_ACCERR,   "write unwriteable addr"},
        { do_pf,        SIGSEGV, SEGV_ACCERR,   "exec unexecutable addr"},
        { do_bad,       SIGBUS,  0,             "unknown 10100"         },
        { do_bad,       SIGBUS,  0,             "unknown 10101"         },
        { do_bad,       SIGBUS,  0,             "unknown 10110"         },
        { do_bad,       SIGBUS,  0,             "unknown 10111"         },
        { do_bad,       SIGBUS,  0,             "unknown 11000"         },
        { do_bad,       SIGBUS,  0,             "unknown 11001"         },
        { do_bad,       SIGBUS,  0,             "unknown 11010"         },
        { do_bad,       SIGBUS,  0,             "unknown 11011"         },
        { do_bad,       SIGBUS,  0,             "unknown 11100"         },
        { do_bad,       SIGBUS,  0,             "unknown 11101"         },
        { do_bad,       SIGBUS,  0,             "unknown 11110"         },
        { do_bad,       SIGBUS,  0,             "unknown 11111"         }
};

void __init hook_fault_code(int nr,
                int (*fn) (unsigned long, unsigned int, struct pt_regs *),
                int sig, int code, const char *name)
{
        if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
                BUG();

        fsr_info[nr].fn   = fn;
        fsr_info[nr].sig  = sig;
        fsr_info[nr].code = code;
        fsr_info[nr].name = name;
}

/*
 * Dispatch a data abort to the relevant handler.
 */
asmlinkage void do_DataAbort(unsigned long addr, unsigned int fsr,
                        struct pt_regs *regs)
{
        const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
        struct siginfo info;

        if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
                return;

        printk(KERN_ALERT "Unhandled fault: %s (0x%03x) at 0x%08lx\n",
               inf->name, fsr, addr);

        clear_siginfo(&info);
        info.si_signo = inf->sig;
        info.si_errno = 0;
        info.si_code = inf->code;
        info.si_addr = (void __user *)addr;
        uc32_notify_die("", regs, &info, fsr, 0);
}

asmlinkage void do_PrefetchAbort(unsigned long addr,
                        unsigned int ifsr, struct pt_regs *regs)
{
        const struct fsr_info *inf = fsr_info + fsr_fs(ifsr);
        struct siginfo info;

        if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
                return;

        printk(KERN_ALERT "Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
               inf->name, ifsr, addr);

        clear_siginfo(&info);
        info.si_signo = inf->sig;
        info.si_errno = 0;
        info.si_code = inf->code;
        info.si_addr = (void __user *)addr;
        uc32_notify_die("", regs, &info, ifsr, 0);
}