fault.c

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/*
 *  linux/arch/alpha/mm/fault.c
 *
 *  Copyright (C) 1995  Linus Torvalds
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <asm/io.h>

#define __EXTERN_INLINE inline
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#undef  __EXTERN_INLINE

#include <linux/signal.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/module.h>

#include <asm/uaccess.h>

extern void die_if_kernel(char *,struct pt_regs *,long, unsigned long *);


/*
 * Force a new ASN for a task.
 */

#ifndef CONFIG_SMP
unsigned long last_asn = ASN_FIRST_VERSION;
#endif

void
__load_new_mm_context(struct mm_struct *next_mm)
{
    unsigned long mmc;
    struct pcb_struct *pcb;

    mmc = __get_new_mm_context(next_mm, smp_processor_id());
    next_mm->context[smp_processor_id()] = mmc;

    pcb = &current_thread_info()->pcb;
    pcb->asn = mmc & HARDWARE_ASN_MASK;
    pcb->ptbr = ((unsigned long) next_mm->pgd - IDENT_ADDR) >> PAGE_SHIFT;

    __reload_thread(pcb);
}


/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to handle_mm_fault().
 *
 * mmcsr:
 *  0 = translation not valid
 *  1 = access violation
 *  2 = fault-on-read
 *  3 = fault-on-execute
 *  4 = fault-on-write
 *
 * cause:
 *  -1 = instruction fetch
 *  0 = load
 *  1 = store
 *
 * Registers $9 through $15 are saved in a block just prior to `regs' and
 * are saved and restored around the call to allow exception code to
 * modify them.
 */

/* Macro for exception fixup code to access integer registers.  */
#define dpf_reg(r)                          \
    (((unsigned long *)regs)[(r) <= 8 ? (r) : (r) <= 15 ? (r)-16 :  \
                 (r) <= 18 ? (r)+8 : (r)-10])

asmlinkage void
do_page_fault(unsigned long address, unsigned long mmcsr,
          long cause, struct pt_regs *regs)
{
    struct vm_area_struct * vma;
    struct mm_struct *mm = current->mm;
    const struct exception_table_entry *fixup;
    int fault, si_code = SEGV_MAPERR;
    siginfo_t info;
    unsigned int flags = (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE |
                  (cause > 0 ? FAULT_FLAG_WRITE : 0));

    /* As of EV6, a load into $31/$f31 is a prefetch, and never faults
       (or is suppressed by the PALcode).  Support that for older CPUs
       by ignoring such an instruction.  */
    if (cause == 0) {
        unsigned int insn;
        __get_user(insn, (unsigned int __user *)regs->pc);
        if ((insn >> 21 & 0x1f) == 0x1f &&
            /* ldq ldl ldt lds ldg ldf ldwu ldbu */
            (1ul << (insn >> 26) & 0x30f00001400ul)) {
            regs->pc += 4;
            return;
        }
    }

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

#ifdef CONFIG_ALPHA_LARGE_VMALLOC
    if (address >= TASK_SIZE)
        goto vmalloc_fault;
#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:
    si_code = SEGV_ACCERR;
    if (cause < 0) {
        if (!(vma->vm_flags & VM_EXEC))
            goto bad_area;
    } else if (!cause) {
        /* Allow reads even for write-only mappings */
        if (!(vma->vm_flags & (VM_READ | VM_WRITE)))
            goto bad_area;
    } else {
        if (!(vma->vm_flags & 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;

             /* 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))
        goto do_sigsegv;

 no_context:
    /* Are we prepared to handle this fault as an exception?  */
    if ((fixup = search_exception_tables(regs->pc)) != 0) {
        unsigned long newpc;
        newpc = fixup_exception(dpf_reg, fixup, regs->pc);
        regs->pc = newpc;
        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 %016lx\n", address);
    die_if_kernel("Oops", regs, cause, (unsigned long*)regs - 16);
    do_exit(SIGKILL);

    /* 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))
        goto no_context;
    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.  */
    info.si_signo = SIGBUS;
    info.si_errno = 0;
    info.si_code = BUS_ADRERR;
    info.si_addr = (void __user *) address;
    force_sig_info(SIGBUS, &info, current);
    if (!user_mode(regs))
        goto no_context;
    return;

 do_sigsegv:
    info.si_signo = SIGSEGV;
    info.si_errno = 0;
    info.si_code = si_code;
    info.si_addr = (void __user *) address;
    force_sig_info(SIGSEGV, &info, current);
    return;

#ifdef CONFIG_ALPHA_LARGE_VMALLOC
 vmalloc_fault:
    if (user_mode(regs))
        goto do_sigsegv;
    else {
        /* Synchronize this task's top level page-table
           with the "reference" page table from init.  */
        long index = pgd_index(address);
        pgd_t *pgd, *pgd_k;

        pgd = current->active_mm->pgd + index;
        pgd_k = swapper_pg_dir + index;
        if (!pgd_present(*pgd) && pgd_present(*pgd_k)) {
            pgd_val(*pgd) = pgd_val(*pgd_k);
            return;
        }
        goto no_context;
    }
#endif
}