6 files changed, 328 insertions, 0 deletions

diff --git a/Documentation/arm/00-INDEX b/Documentation/arm/00-INDEX
index ecf7d04bca26..91c24a1e8a9e 100644
--- a/Documentation/arm/00-INDEX
+++ b/Documentation/arm/00-INDEX
@@ -34,3 +34,5 @@ memory.txt
         - description of the virtual memory layout
 nwfpe/
         - NWFPE floating point emulator documentation
+swp_emulation
+        - SWP/SWPB emulation handler/logging description
diff --git a/Documentation/arm/swp_emulation b/Documentation/arm/swp_emulation
new file mode 100644
index 000000000000..af903d22fd93
--- /dev/null
+++ b/Documentation/arm/swp_emulation
@@ -0,0 +1,27 @@
+Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
+---------------------------------------------------------------------
+
+ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommeds
+moving to the load-locked/store-conditional instructions LDREX and STREX.
+
+ARMv7 multiprocessing extensions introduce the ability to disable these
+instructions, triggering an undefined instruction exception when executed.
+Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB
+sequence. If a memory access fault (an abort) occurs, a segmentation fault is
+signalled to the triggering process.
+
+/proc/cpu/swp_emulation holds some statistics/information, including the PID of
+the last process to trigger the emulation to be invocated. For example:
+---
+Emulated SWP:           12
+Emulated SWPB:          0
+Aborted SWP{B}:         1
+Last process:           314
+---
+
+NOTE: when accessing uncached shared regions, LDREX/STREX rely on an external
+transaction monitoring block called a global monitor to maintain update
+atomicity. If your system does not implement a global monitor, this option can
+cause programs that perform SWP operations to uncached memory to deadlock, as
+the STREX operation will always fail.
+
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 5b9b268f4fbb..119a6bb59bde 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -42,6 +42,7 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_ARM_UNWIND)        += unwind.o
 obj-$(CONFIG_HAVE_TCM)          += tcm.o
 obj-$(CONFIG_CRASH_DUMP)        += crash_dump.o
+obj-$(CONFIG_SWP_EMULATE)       += swp_emulate.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)        += hw_breakpoint.o
 
 obj-$(CONFIG_CRUNCH)            += crunch.o crunch-bits.o
diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
new file mode 100644
index 000000000000..7a5760922914
--- /dev/null
+++ b/arch/arm/kernel/swp_emulate.c
@@ -0,0 +1,267 @@
+/*
+ *  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);
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 6d05f79a8cd2..8493ed04797a 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -636,6 +636,33 @@ config ARM_THUMBEE
           Say Y here if you have a CPU with the ThumbEE extension and code to
           make use of it. Say N for code that can run on CPUs without ThumbEE.
 
+config SWP_EMULATE
+        bool "Emulate SWP/SWPB instructions"
+        depends on CPU_V7
+        select HAVE_PROC_CPU if PROC_FS
+        default y if SMP
+        help
+          ARMv6 architecture deprecates use of the SWP/SWPB instructions.
+          ARMv7 multiprocessing extensions introduce the ability to disable
+          these instructions, triggering an undefined instruction exception
+          when executed. Say Y here to enable software emulation of these
+          instructions for userspace (not kernel) using LDREX/STREX.
+          Also creates /proc/cpu/swp_emulation for statistics.
+
+          In some older versions of glibc [<=2.8] SWP is used during futex
+          trylock() operations with the assumption that the code will not
+          be preempted. This invalid assumption may be more likely to fail
+          with SWP emulation enabled, leading to deadlock of the user
+          application.
+
+          NOTE: when accessing uncached shared regions, LDREX/STREX rely
+          on an external transaction monitoring block called a global
+          monitor to maintain update atomicity. If your system does not
+          implement a global monitor, this option can cause programs that
+          perform SWP operations to uncached memory to deadlock.
+
+          If unsure, say Y.
+
 config CPU_BIG_ENDIAN
         bool "Build big-endian kernel"
         depends on ARCH_SUPPORTS_BIG_ENDIAN
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index cfc11afab1fb..2b5b20baf80d 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -314,6 +314,10 @@ __v7_setup:
 #ifdef CONFIG_CPU_ENDIAN_BE8
         orr     r6, r6, #1 << 25                @ big-endian page tables
 #endif
+#ifdef CONFIG_SWP_EMULATE
+        orr     r5, r5, #(1 << 10)              @ set SW bit in "clear"
+        bic     r6, r6, #(1 << 10)              @ clear it in "mmuset"
+#endif
         mrc     p15, 0, r0, c1, c0, 0           @ read control register
         bic     r0, r0, r5                      @ clear bits them
         orr     r0, r0, r6                      @ set them