// TODO VM_EXEC flag work-around, cache aliasing
/*
 * arch/xtensa/mm/fault.c
 *
 * 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.
 *
 * Copyright (C) 2001 - 2005 Tensilica Inc.
 *
 * Chris Zankel <chris@zankel.net>
 * Joe Taylor   <joe@tensilica.com, joetylr@yahoo.com>
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/hardirq.h>
#include <asm/mmu_context.h>
#include <asm/cacheflush.h>
#include <asm/hardirq.h>
#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/pgalloc.h>

unsigned long asid_cache = ASID_USER_FIRST;
void bad_page_fault(struct pt_regs*, unsigned long, int);

#undef DEBUG_PAGE_FAULT

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 *
 * Note: does not handle Miss and MultiHit.
 */

void do_page_fault(struct pt_regs *regs)
{
        struct vm_area_struct * vma;
        struct mm_struct *mm = current->mm;
        unsigned int exccause = regs->exccause;
        unsigned int address = regs->excvaddr;
        siginfo_t info;

        int is_write, is_exec;
        int fault;

        info.si_code = SEGV_MAPERR;

        /* We fault-in kernel-space virtual memory on-demand. The
         * 'reference' page table is init_mm.pgd.
         */
        if (address >= TASK_SIZE && !user_mode(regs))
                goto vmalloc_fault;

        /* If we're in an interrupt or have no user
         * context, we must not take the fault..
         */
        if (in_atomic() || !mm) {
                bad_page_fault(regs, address, SIGSEGV);
                return;
        }

        is_write = (exccause == EXCCAUSE_STORE_CACHE_ATTRIBUTE) ? 1 : 0;
        is_exec =  (exccause == EXCCAUSE_ITLB_PRIVILEGE ||
                    exccause == EXCCAUSE_ITLB_MISS ||
                    exccause == EXCCAUSE_FETCH_CACHE_ATTRIBUTE) ? 1 : 0;

#ifdef DEBUG_PAGE_FAULT
        printk("[%s:%d:%08x:%d:%08x:%s%s]\n", current->comm, current->pid,
               address, exccause, regs->pc, is_write? "w":"", is_exec? "x":"");
#endif

        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;

        /* Ok, we have a good vm_area for this memory access, so
         * we can handle it..
         */

good_area:
        info.si_code = SEGV_ACCERR;

        if (is_write) {
                if (!(vma->vm_flags & VM_WRITE))
                        goto bad_area;
        } else if (is_exec) {
                if (!(vma->vm_flags & VM_EXEC))
                        goto bad_area;
        } else  /* Allow read even from write-only pages. */
                if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
                        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.
         */
survive:
        fault = handle_mm_fault(mm, vma, address, is_write ? FAULT_FLAG_WRITE : 0);
        if (unlikely(fault & VM_FAULT_ERROR)) {
                if (fault & VM_FAULT_OOM)
                        goto out_of_memory;
                else if (fault & VM_FAULT_SIGBUS)
                        goto do_sigbus;
                BUG();
        }
        if (fault & VM_FAULT_MAJOR)
                current->maj_flt++;
        else
                current->min_flt++;

        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);
        if (user_mode(regs)) {
                current->thread.bad_vaddr = address;
                current->thread.error_code = is_write;
                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, current);
                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 (is_global_init(current)) {
                yield();
                down_read(&mm->mmap_sem);
                goto survive;
        }
        printk("VM: killing process %s\n", current->comm);
        if (user_mode(regs))
                do_group_exit(SIGKILL);
        bad_page_fault(regs, address, SIGKILL);
        return;

do_sigbus:
        up_read(&mm->mmap_sem);

        /* Send a sigbus, regardless of whether we were in kernel
         * or user mode.
         */
        current->thread.bad_vaddr = address;
        info.si_code = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (void *) address;
        force_sig_info(SIGBUS, &info, current);

        /* Kernel mode? Handle exceptions or die */
        if (!user_mode(regs))
                bad_page_fault(regs, address, SIGBUS);

vmalloc_fault:
        {
                /* Synchronize this task's top level page-table
                 * with the 'reference' page table.
                 */
                struct mm_struct *act_mm = current->active_mm;
                int index = pgd_index(address);
                pgd_t *pgd, *pgd_k;
                pmd_t *pmd, *pmd_k;
                pte_t *pte_k;

                if (act_mm == NULL)
                        goto bad_page_fault;

                pgd = act_mm->pgd + index;
                pgd_k = init_mm.pgd + index;

                if (!pgd_present(*pgd_k))
                        goto bad_page_fault;

                pgd_val(*pgd) = pgd_val(*pgd_k);

                pmd = pmd_offset(pgd, address);
                pmd_k = pmd_offset(pgd_k, address);
                if (!pmd_present(*pmd) || !pmd_present(*pmd_k))
                        goto bad_page_fault;

                pmd_val(*pmd) = pmd_val(*pmd_k);
                pte_k = pte_offset_kernel(pmd_k, address);

                if (!pte_present(*pte_k))
                        goto bad_page_fault;
                return;
        }
bad_page_fault:
        bad_page_fault(regs, address, SIGKILL);
        return;
}


void
bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
        extern void die(const char*, struct pt_regs*, long);
        const struct exception_table_entry *entry;

        /* Are we prepared to handle this kernel fault?  */
        if ((entry = search_exception_tables(regs->pc)) != NULL) {
#ifdef DEBUG_PAGE_FAULT
                printk(KERN_DEBUG "%s: Exception at pc=%#010lx (%lx)\n",
                                current->comm, regs->pc, entry->fixup);
#endif
                current->thread.bad_uaddr = address;
                regs->pc = entry->fixup;
                return;
        }

        /* Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
        printk(KERN_ALERT "Unable to handle kernel paging request at virtual "
               "address %08lx\n pc = %08lx, ra = %08lx\n",
               address, regs->pc, regs->areg[0]);
        die("Oops", regs, sig);
        do_exit(sig);
}