fault.c

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// 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 - 2010 Tensilica Inc.
 *
 * Chris Zankel <[email protected]>
 * Joe Taylor   <[email protected], [email protected]>
 */

#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/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;
    unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;

    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

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;

    /* 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;
        flags |= FAULT_FLAG_WRITE;
    } 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.
     */
    fault = handle_mm_fault(mm, 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_SIGBUS)
            goto do_sigbus;
        BUG();
    }
    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;

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

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);
}