diff options
| -rw-r--r-- | Documentation/arm/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/arm/swp_emulation | 27 | ||||
| -rw-r--r-- | arch/arm/kernel/Makefile | 1 | ||||
| -rw-r--r-- | arch/arm/kernel/swp_emulate.c | 267 | ||||
| -rw-r--r-- | arch/arm/mm/Kconfig | 27 | ||||
| -rw-r--r-- | arch/arm/mm/proc-v7.S | 4 |
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 |
