--- /dev/null
+/*
+ * 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);
git.openpandora.org / pandora-kernel.git / commitdiff