/*
 * Memory fault handling for Hexagon
 *
 * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/*
 * Page fault handling for the Hexagon Virtual Machine.
 * Can also be called by a native port emulating the HVM
 * execptions.
 */

#include <asm/pgtable.h>
#include <asm/traps.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/signal.h>
#include <linux/extable.h>
#include <linux/hardirq.h>

/*
 * Decode of hardware exception sends us to one of several
 * entry points.  At each, we generate canonical arguments
 * for handling by the abstract memory management code.
 */
#define FLT_IFETCH     -1
#define FLT_LOAD        0
#define FLT_STORE       1


/*
 * Canonical page fault handler
 */
void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
{
        struct vm_area_struct *vma;
        struct mm_struct *mm = current->mm;
        int si_signo;
        int si_code = SEGV_MAPERR;
        vm_fault_t fault;
        const struct exception_table_entry *fixup;
        unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

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

        local_irq_enable();

        if (user_mode(regs))
                flags |= FAULT_FLAG_USER;
retry:
        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 (expand_stack(vma, address))
                goto bad_area;

good_area:
        /* Address space is OK.  Now check access rights. */
        si_code = SEGV_ACCERR;

        switch (cause) {
        case FLT_IFETCH:
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
                break;
        case FLT_LOAD:
                if (!(vma->vm_flags & VM_READ))
                        goto bad_area;
                break;
        case FLT_STORE:
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
                flags |= FAULT_FLAG_WRITE;
                break;
        }

        fault = handle_mm_fault(vma, address, flags);

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

        /* The most common case -- we are done. */
        if (likely(!(fault & VM_FAULT_ERROR))) {
                if (flags & FAULT_FLAG_ALLOW_RETRY) {
                        if (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;
                                goto retry;
                        }
                }

                up_read(&mm->mmap_sem);
                return;
        }

        up_read(&mm->mmap_sem);

        /* Handle copyin/out exception cases */
        if (!user_mode(regs))
                goto no_context;

        if (fault & VM_FAULT_OOM) {
                pagefault_out_of_memory();
                return;
        }

        /* User-mode address is in the memory map, but we are
         * unable to fix up the page fault.
         */
        if (fault & VM_FAULT_SIGBUS) {
                si_signo = SIGBUS;
                si_code = BUS_ADRERR;
        }
        /* Address is not in the memory map */
        else {
                si_signo = SIGSEGV;
                si_code  = SEGV_ACCERR;
        }
        force_sig_fault(si_signo, si_code, (void __user *)address, current);
        return;

bad_area:
        up_read(&mm->mmap_sem);

        if (user_mode(regs)) {
                force_sig_fault(SIGSEGV, si_code, (void __user *)address, current);
                return;
        }
        /* Kernel-mode fault falls through */

no_context:
        fixup = search_exception_tables(pt_elr(regs));
        if (fixup) {
                pt_set_elr(regs, fixup->fixup);
                return;
        }

        /* Things are looking very, very bad now */
        bust_spinlocks(1);
        printk(KERN_EMERG "Unable to handle kernel paging request at "
                "virtual address 0x%08lx, regs %p\n", address, regs);
        die("Bad Kernel VA", regs, SIGKILL);
}


void read_protection_fault(struct pt_regs *regs)
{
        unsigned long badvadr = pt_badva(regs);

        do_page_fault(badvadr, FLT_LOAD, regs);
}

void write_protection_fault(struct pt_regs *regs)
{
        unsigned long badvadr = pt_badva(regs);

        do_page_fault(badvadr, FLT_STORE, regs);
}

void execute_protection_fault(struct pt_regs *regs)
{
        unsigned long badvadr = pt_badva(regs);

        do_page_fault(badvadr, FLT_IFETCH, regs);
}