/*
 *  arch/microblaze/mm/fault.c
 *
 *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
 *
 *  Derived from "arch/ppc/mm/fault.c"
 *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
 *
 *  Derived from "arch/i386/mm/fault.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Modified by Cort Dougan and Paul Mackerras.
 *
 * This file is subject to the terms and conditions of the GNU General
 * Public License.  See the file COPYING in the main directory of this
 * archive for more details.
 *
 */

#include <linux/extable.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/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <linux/mmu_context.h>
#include <linux/uaccess.h>
#include <asm/exceptions.h>

static unsigned long pte_misses;        /* updated by do_page_fault() */
static unsigned long pte_errors;        /* updated by do_page_fault() */

/*
 * Check whether the instruction at regs->pc is a store using
 * an update addressing form which will update r1.
 */
static int store_updates_sp(struct pt_regs *regs)
{
        unsigned int inst;

        if (get_user(inst, (unsigned int __user *)regs->pc))
                return 0;
        /* check for 1 in the rD field */
        if (((inst >> 21) & 0x1f) != 1)
                return 0;
        /* check for store opcodes */
        if ((inst & 0xd0000000) == 0xd0000000)
                return 1;
        return 0;
}


/*
 * bad_page_fault is called when we have a bad access from the kernel.
 * It is called from do_page_fault above and from some of the procedures
 * in traps.c.
 */
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
        const struct exception_table_entry *fixup;
/* MS: no context */
        /* Are we prepared to handle this fault?  */
        fixup = search_exception_tables(regs->pc);
        if (fixup) {
                regs->pc = fixup->fixup;
                return;
        }

        /* kernel has accessed a bad area */
        die("kernel access of bad area", regs, sig);
}

/*
 * The error_code parameter is ESR for a data fault,
 * 0 for an instruction fault.
 */
void do_page_fault(struct pt_regs *regs, unsigned long address,
                   unsigned long error_code)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm = current->mm;
        int code = SEGV_MAPERR;
        int is_write = error_code & ESR_S;
        vm_fault_t fault;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

        regs->ear = address;
        regs->esr = error_code;

        /* On a kernel SLB miss we can only check for a valid exception entry */
        if (unlikely(kernel_mode(regs) && (address >= TASK_SIZE))) {
                pr_warn("kernel task_size exceed");
                _exception(SIGSEGV, regs, code, address);
        }

        /* for instr TLB miss and instr storage exception ESR_S is undefined */
        if ((error_code & 0x13) == 0x13 || (error_code & 0x11) == 0x11)
                is_write = 0;

        if (unlikely(faulthandler_disabled() || !mm)) {
                if (kernel_mode(regs))
                        goto bad_area_nosemaphore;

                /* faulthandler_disabled() in user mode is really bad,
                   as is current->mm == NULL. */
                pr_emerg("Page fault in user mode with faulthandler_disabled(), mm = %p\n",
                         mm);
                pr_emerg("r15 = %lx  MSR = %lx\n",
                       regs->r15, regs->msr);
                die("Weird page fault", regs, SIGSEGV);
        }

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;

        /* When running in the kernel we expect faults to occur only to
         * addresses in user space.  All other faults represent errors in the
         * kernel and should generate an OOPS.  Unfortunately, in the case of an
         * erroneous fault occurring in a code path which already holds mmap_sem
         * we will deadlock attempting to validate the fault against the
         * address space.  Luckily the kernel only validly references user
         * space from well defined areas of code, which are listed in the
         * exceptions table.
         *
         * As the vast majority of faults will be valid we will only perform
         * the source reference check when there is a possibility of a deadlock.
         * Attempt to lock the address space, if we cannot we then validate the
         * source.  If this is invalid we can skip the address space check,
         * thus avoiding the deadlock.
         */
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                if (kernel_mode(regs) && !search_exception_tables(regs->pc))
                        goto bad_area_nosemaphore;

retry:
                down_read(&mm->mmap_sem);
        }

        vma = find_vma(mm, address);
        if (unlikely(!vma))
                goto bad_area;

        if (vma->vm_start <= address)
                goto good_area;

        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
                goto bad_area;

        if (unlikely(!is_write))
                goto bad_area;

        /*
         * N.B. The ABI allows programs to access up to
         * a few hundred bytes below the stack pointer (TBD).
         * The kernel signal delivery code writes up to about 1.5kB
         * below the stack pointer (r1) before decrementing it.
         * The exec code can write slightly over 640kB to the stack
         * before setting the user r1.  Thus we allow the stack to
         * expand to 1MB without further checks.
         */
        if (unlikely(address + 0x100000 < vma->vm_end)) {

                /* get user regs even if this fault is in kernel mode */
                struct pt_regs *uregs = current->thread.regs;
                if (uregs == NULL)
                        goto bad_area;

                /*
                 * A user-mode access to an address a long way below
                 * the stack pointer is only valid if the instruction
                 * is one which would update the stack pointer to the
                 * address accessed if the instruction completed,
                 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
                 * (or the byte, halfword, float or double forms).
                 *
                 * If we don't check this then any write to the area
                 * between the last mapped region and the stack will
                 * expand the stack rather than segfaulting.
                 */
                if (address + 2048 < uregs->r1
                        && (kernel_mode(regs) || !store_updates_sp(regs)))
                                goto bad_area;
        }
        if (expand_stack(vma, address))
                goto bad_area;

good_area:
        code = SEGV_ACCERR;

        /* a write */
        if (unlikely(is_write)) {
                if (unlikely(!(vma->vm_flags & VM_WRITE)))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
        /* a read */
        } else {
                /* protection fault */
                if (unlikely(error_code & 0x08000000))
                        goto bad_area;
                if (unlikely(!(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(vma, address, flags);

        if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
                return;

        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
                        goto out_of_memory;
                else if (fault & VM_FAULT_SIGSEGV)
                        goto bad_area;
                else if (fault & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
        }

        if (flags & FAULT_FLAG_ALLOW_RETRY) {
                if (unlikely(fault & VM_FAULT_MAJOR))
                        current->maj_flt++;
                else
                        current->min_flt++;
                if (fault & VM_FAULT_RETRY) {
                        flags &= ~FAULT_FLAG_ALLOW_RETRY;
                        flags |= FAULT_FLAG_TRIED;

                        /*
                         * No need to up_read(&mm->mmap_sem) as we would
                         * have already released it in __lock_page_or_retry
                         * in mm/filemap.c.
                         */

                        goto retry;
                }
        }

        up_read(&mm->mmap_sem);

        /*
         * keep track of tlb+htab misses that are good addrs but
         * just need pte's created via handle_mm_fault()
         * -- Cort
         */
        pte_misses++;
        return;

bad_area:
        up_read(&mm->mmap_sem);

bad_area_nosemaphore:
        pte_errors++;

        /* User mode accesses cause a SIGSEGV */
        if (user_mode(regs)) {
                _exception(SIGSEGV, regs, code, address);
                return;
        }

        bad_page_fault(regs, address, SIGSEGV);
        return;

/*
 * 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);
        if (!user_mode(regs))
                bad_page_fault(regs, address, SIGKILL);
        else
                pagefault_out_of_memory();
        return;

do_sigbus:
        up_read(&mm->mmap_sem);
        if (user_mode(regs)) {
                force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, current);
                return;
        }
        bad_page_fault(regs, address, SIGBUS);
}