Logo Search packages:      
Sourcecode: linux version File versions  Download package

swp_emulate.c

/*
 *  linux/arch/arm/kernel/swp_emulate.c
 *
 *  Copyright (C) 2009 ARM Limited
 *  __user_* functions adapted from include/asm/uaccess.h
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 *  Implements emulation of the SWP/SWPB instructions using load-exclusive and
 *  store-exclusive for processors that have them disabled (or future ones that
 *  might not implement them).
 *
 *  Syntax of SWP{B} instruction: SWP{B}<c> <Rt>, <Rt2>, [<Rn>]
 *  Where: Rt  = destination
 *       Rt2 = source
 *       Rn  = address
 */

#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/syscalls.h>
#include <linux/perf_event.h>

#include <asm/traps.h>
#include <asm/uaccess.h>

/*
 * Error-checking SWP macros implemented using ldrex{b}/strex{b}
 */
#define __user_swpX_asm(data, addr, res, temp, B)           \
      __asm__ __volatile__(                           \
      "     mov         %2, %1\n"               \
      "0:   ldrex"B"    %1, [%3]\n"             \
      "1:   strex"B"    %0, %2, [%3]\n"               \
      "     cmp         %0, #0\n"               \
      "     movne       %0, %4\n"               \
      "2:\n"                                          \
      "     .section     .fixup,\"ax\"\n"       \
      "     .align            2\n"                    \
      "3:   mov         %0, %5\n"               \
      "     b           2b\n"                   \
      "     .previous\n"                              \
      "     .section     __ex_table,\"a\"\n"          \
      "     .align            3\n"                    \
      "     .long       0b, 3b\n"               \
      "     .long       1b, 3b\n"               \
      "     .previous"                          \
      : "=&r" (res), "+r" (data), "=&r" (temp)        \
      : "r" (addr), "i" (-EAGAIN), "i" (-EFAULT)            \
      : "cc", "memory")

#define __user_swp_asm(data, addr, res, temp) \
      __user_swpX_asm(data, addr, res, temp, "")
#define __user_swpb_asm(data, addr, res, temp) \
      __user_swpX_asm(data, addr, res, temp, "b")

/*
 * Macros/defines for extracting register numbers from instruction.
 */
#define EXTRACT_REG_NUM(instruction, offset) \
      (((instruction) & (0xf << (offset))) >> (offset))
#define RN_OFFSET  16
#define RT_OFFSET  12
#define RT2_OFFSET  0
/*
 * Bit 22 of the instruction encoding distinguishes between
 * the SWP and SWPB variants (bit set means SWPB).
 */
#define TYPE_SWPB (1 << 22)

static unsigned long swpcounter;
static unsigned long swpbcounter;
static unsigned long abtcounter;
static pid_t         previous_pid;

#ifdef CONFIG_PROC_FS
static int proc_read_status(char *page, char **start, off_t off, int count,
                      int *eof, void *data)
{
      char *p = page;
      int len;

      p += sprintf(p, "Emulated SWP:\t\t%lu\n", swpcounter);
      p += sprintf(p, "Emulated SWPB:\t\t%lu\n", swpbcounter);
      p += sprintf(p, "Aborted SWP{B}:\t\t%lu\n", abtcounter);
      if (previous_pid != 0)
            p += sprintf(p, "Last process:\t\t%d\n", previous_pid);

      len = (p - page) - off;
      if (len < 0)
            len = 0;

      *eof = (len <= count) ? 1 : 0;
      *start = page + off;

      return len;
}
#endif

/*
 * Set up process info to signal segmentation fault - called on access error.
 */
static void set_segfault(struct pt_regs *regs, unsigned long addr)
{
      siginfo_t info;

      if (find_vma(current->mm, addr) == NULL)
            info.si_code = SEGV_MAPERR;
      else
            info.si_code = SEGV_ACCERR;

      info.si_signo = SIGSEGV;
      info.si_errno = 0;
      info.si_addr  = (void *) instruction_pointer(regs);

      pr_debug("SWP{B} emulation: access caused memory abort!\n");
      arm_notify_die("Illegal memory access", regs, &info, 0, 0);

      abtcounter++;
}

static int emulate_swpX(unsigned int address, unsigned int *data,
                  unsigned int type)
{
      unsigned int res = 0;

      if ((type != TYPE_SWPB) && (address & 0x3)) {
            /* SWP to unaligned address not permitted */
            pr_debug("SWP instruction on unaligned pointer!\n");
            return -EFAULT;
      }

      while (1) {
            unsigned long temp;

            /*
             * Barrier required between accessing protected resource and
             * releasing a lock for it. Legacy code might not have done
             * this, and we cannot determine that this is not the case
             * being emulated, so insert always.
             */
            smp_mb();

            if (type == TYPE_SWPB)
                  __user_swpb_asm(*data, address, res, temp);
            else
                  __user_swp_asm(*data, address, res, temp);

            if (likely(res != -EAGAIN) || signal_pending(current))
                  break;

            cond_resched();
      }

      if (res == 0) {
            /*
             * Barrier also required between aquiring a lock for a
             * protected resource and accessing the resource. Inserted for
             * same reason as above.
             */
            smp_mb();

            if (type == TYPE_SWPB)
                  swpbcounter++;
            else
                  swpcounter++;
      }

      return res;
}

/*
 * swp_handler logs the id of calling process, dissects the instruction, sanity
 * checks the memory location, calls emulate_swpX for the actual operation and
 * deals with fixup/error handling before returning
 */
static int swp_handler(struct pt_regs *regs, unsigned int instr)
{
      unsigned int address, destreg, data, type;
      unsigned int res = 0;

      perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, 0, regs, regs->ARM_pc);

      if (current->pid != previous_pid) {
            pr_debug("\"%s\" (%ld) uses deprecated SWP{B} instruction\n",
                   current->comm, (unsigned long)current->pid);
            previous_pid = current->pid;
      }

      address = regs->uregs[EXTRACT_REG_NUM(instr, RN_OFFSET)];
      data  = regs->uregs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
      destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);

      type = instr & TYPE_SWPB;

      pr_debug("addr in r%d->0x%08x, dest is r%d, source in r%d->0x%08x)\n",
             EXTRACT_REG_NUM(instr, RN_OFFSET), address,
             destreg, EXTRACT_REG_NUM(instr, RT2_OFFSET), data);

      /* Check access in reasonable access range for both SWP and SWPB */
      if (!access_ok(VERIFY_WRITE, (address & ~3), 4)) {
            pr_debug("SWP{B} emulation: access to %p not allowed!\n",
                   (void *)address);
            res = -EFAULT;
      } else {
            res = emulate_swpX(address, &data, type);
      }

      if (res == 0) {
            /*
             * On successful emulation, revert the adjustment to the PC
             * made in kernel/traps.c in order to resume execution at the
             * instruction following the SWP{B}.
             */
            regs->ARM_pc += 4;
            regs->uregs[destreg] = data;
      } else if (res == -EFAULT) {
            /*
             * Memory errors do not mean emulation failed.
             * Set up signal info to return SEGV, then return OK
             */
            set_segfault(regs, address);
      }

      return 0;
}

/*
 * Only emulate SWP/SWPB executed in ARM state/User mode.
 * The kernel must be SWP free and SWP{B} does not exist in Thumb/ThumbEE.
 */
static struct undef_hook swp_hook = {
      .instr_mask = 0x0fb00ff0,
      .instr_val  = 0x01000090,
      .cpsr_mask  = MODE_MASK | PSR_T_BIT | PSR_J_BIT,
      .cpsr_val   = USR_MODE,
      .fn       = swp_handler
};

/*
 * Register handler and create status file in /proc/cpu
 * Invoked as late_initcall, since not needed before init spawned.
 */
static int __init swp_emulation_init(void)
{
#ifdef CONFIG_PROC_FS
      struct proc_dir_entry *res;

      res = create_proc_entry("cpu/swp_emulation", S_IRUGO, NULL);

      if (!res)
            return -ENOMEM;

      res->read_proc = proc_read_status;
#endif /* CONFIG_PROC_FS */

      printk(KERN_NOTICE "Registering SWP/SWPB emulation handler\n");
      register_undef_hook(&swp_hook);

      return 0;
}

late_initcall(swp_emulation_init);

Generated by  Doxygen 1.6.0   Back to index