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trap.c

/*
 * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 * Licensed under the GPL
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/hardirq.h>
#include <asm/current.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include "arch.h"
#include "as-layout.h"
#include "kern_util.h"
#include "os.h"
#include "sysdep/sigcontext.h"

/*
 * Note this is constrained to return 0, -EFAULT, -EACCESS, -ENOMEM by
 * segv().
 */
int handle_page_fault(unsigned long address, unsigned long ip,
                  int is_write, int is_user, int *code_out)
{
      struct mm_struct *mm = current->mm;
      struct vm_area_struct *vma;
      pgd_t *pgd;
      pud_t *pud;
      pmd_t *pmd;
      pte_t *pte;
      int err = -EFAULT;

      *code_out = SEGV_MAPERR;

      /*
       * If the fault was during atomic operation, don't take the fault, just
       * fail.
       */
      if (in_atomic())
            goto out_nosemaphore;

      down_read(&mm->mmap_sem);
      vma = find_vma(mm, address);
      if (!vma)
            goto out;
      else if (vma->vm_start <= address)
            goto good_area;
      else if (!(vma->vm_flags & VM_GROWSDOWN))
            goto out;
      else if (is_user && !ARCH_IS_STACKGROW(address))
            goto out;
      else if (expand_stack(vma, address))
            goto out;

good_area:
      *code_out = SEGV_ACCERR;
      if (is_write && !(vma->vm_flags & VM_WRITE))
            goto out;

      /* Don't require VM_READ|VM_EXEC for write faults! */
      if (!is_write && !(vma->vm_flags & (VM_READ | VM_EXEC)))
            goto out;

      do {
            int fault;
survive:
            fault = handle_mm_fault(mm, vma, address, is_write);
            if (unlikely(fault & VM_FAULT_ERROR)) {
                  if (fault & VM_FAULT_OOM) {
                        err = -ENOMEM;
                        goto out_of_memory;
                  } else if (fault & VM_FAULT_SIGBUS) {
                        err = -EACCES;
                        goto out;
                  }
                  BUG();
            }
            if (fault & VM_FAULT_MAJOR)
                  current->maj_flt++;
            else
                  current->min_flt++;

            pgd = pgd_offset(mm, address);
            pud = pud_offset(pgd, address);
            pmd = pmd_offset(pud, address);
            pte = pte_offset_kernel(pmd, address);
      } while (!pte_present(*pte));
      err = 0;
      /*
       * The below warning was added in place of
       *    pte_mkyoung(); if (is_write) pte_mkdirty();
       * If it's triggered, we'd see normally a hang here (a clean pte is
       * marked read-only to emulate the dirty bit).
       * However, the generic code can mark a PTE writable but clean on a
       * concurrent read fault, triggering this harmlessly. So comment it out.
       */
#if 0
      WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
#endif
      flush_tlb_page(vma, address);
out:
      up_read(&mm->mmap_sem);
out_nosemaphore:
      return err;

/*
 * 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:
      if (is_global_init(current)) {
            up_read(&mm->mmap_sem);
            yield();
            down_read(&mm->mmap_sem);
            goto survive;
      }
      goto out;
}

static void bad_segv(struct faultinfo fi, unsigned long ip)
{
      struct siginfo si;

      si.si_signo = SIGSEGV;
      si.si_code = SEGV_ACCERR;
      si.si_addr = (void __user *) FAULT_ADDRESS(fi);
      current->thread.arch.faultinfo = fi;
      force_sig_info(SIGSEGV, &si, current);
}

static void segv_handler(int sig, struct uml_pt_regs *regs)
{
      struct faultinfo * fi = UPT_FAULTINFO(regs);

      if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
            bad_segv(*fi, UPT_IP(regs));
            return;
      }
      segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
}

/*
 * We give a *copy* of the faultinfo in the regs to segv.
 * This must be done, since nesting SEGVs could overwrite
 * the info in the regs. A pointer to the info then would
 * give us bad data!
 */
unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
               struct uml_pt_regs *regs)
{
      struct siginfo si;
      jmp_buf *catcher;
      int err;
      int is_write = FAULT_WRITE(fi);
      unsigned long address = FAULT_ADDRESS(fi);

      if (!is_user && (address >= start_vm) && (address < end_vm)) {
            flush_tlb_kernel_vm();
            return 0;
      }
      else if (current->mm == NULL) {
            show_regs(container_of(regs, struct pt_regs, regs));
            panic("Segfault with no mm");
      }

      if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
            err = handle_page_fault(address, ip, is_write, is_user,
                              &si.si_code);
      else {
            err = -EFAULT;
            /*
             * A thread accessed NULL, we get a fault, but CR2 is invalid.
             * This code is used in __do_copy_from_user() of TT mode.
             * XXX tt mode is gone, so maybe this isn't needed any more
             */
            address = 0;
      }

      catcher = current->thread.fault_catcher;
      if (!err)
            return 0;
      else if (catcher != NULL) {
            current->thread.fault_addr = (void *) address;
            UML_LONGJMP(catcher, 1);
      }
      else if (current->thread.fault_addr != NULL)
            panic("fault_addr set but no fault catcher");
      else if (!is_user && arch_fixup(ip, regs))
            return 0;

      if (!is_user) {
            show_regs(container_of(regs, struct pt_regs, regs));
            panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
                  address, ip);
      }

      if (err == -EACCES) {
            si.si_signo = SIGBUS;
            si.si_errno = 0;
            si.si_code = BUS_ADRERR;
            si.si_addr = (void __user *)address;
            current->thread.arch.faultinfo = fi;
            force_sig_info(SIGBUS, &si, current);
      } else if (err == -ENOMEM) {
            printk(KERN_INFO "VM: killing process %s\n", current->comm);
            do_exit(SIGKILL);
      } else {
            BUG_ON(err != -EFAULT);
            si.si_signo = SIGSEGV;
            si.si_addr = (void __user *) address;
            current->thread.arch.faultinfo = fi;
            force_sig_info(SIGSEGV, &si, current);
      }
      return 0;
}

void relay_signal(int sig, struct uml_pt_regs *regs)
{
      if (arch_handle_signal(sig, regs))
            return;

      if (!UPT_IS_USER(regs)) {
            if (sig == SIGBUS)
                  printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
                         "mount likely just ran out of space\n");
            panic("Kernel mode signal %d", sig);
      }

      current->thread.arch.faultinfo = *UPT_FAULTINFO(regs);
      force_sig(sig, current);
}

static void bus_handler(int sig, struct uml_pt_regs *regs)
{
      if (current->thread.fault_catcher != NULL)
            UML_LONGJMP(current->thread.fault_catcher, 1);
      else relay_signal(sig, regs);
}

static void winch(int sig, struct uml_pt_regs *regs)
{
      do_IRQ(WINCH_IRQ, regs);
}

const struct kern_handlers handlinfo_kern = {
      .relay_signal = relay_signal,
      .winch = winch,
      .bus_handler = bus_handler,
      .page_fault = segv_handler,
      .sigio_handler = sigio_handler,
      .timer_handler = timer_handler
};

void trap_init(void)
{
}

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