arm64: emulate the swp/swpb instruction (2f668101) · Commits · e / devices / android_kernel_sony_msm8994

arch/arm64/Kconfig

+26 −0

Original line number	Diff line number	Diff line
		@@ -244,6 +244,31 @@ config HOTPLUG_CPU

		source kernel/Kconfig.preempt

		config SWP_EMULATE
		bool "Emulate SWP/SWPB instructions"
		help
		ARMv6 architecture deprecates use of the SWP/SWPB instructions. ARMv8
		oblosetes the use of 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 HZ
		int
		default 100
		@@ -287,6 +312,7 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
		config ARMV7_COMPAT
		bool "Kernel support for ARMv7 applications"
		depends on COMPAT
		select SWP_EMULATE
		help
		This option enables features that allow that ran on an ARMv7 or older
		processor to continue functioning.

arch/arm64/kernel/Makefile

+2 −0

Original line number	Diff line number	Diff line
		@@ -22,6 +22,8 @@ arm64-obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
		arm64-obj-$(CONFIG_ARM64_CPU_SUSPEND) += sleep.o suspend.o
		arm64-obj-$(CONFIG_JUMP_LABEL) += jump_label.o

		obj-$(CONFIG_SWP_EMULATE) += swp_emulate.o

		obj-y += $(arm64-obj-y) vdso/
		obj-m += $(arm64-obj-m)
		head-y := head.o

arch/arm64/kernel/swp_emulate.c

0 → 100644

+155 −0

Original line number	Diff line number	Diff line
		/*
		* Derived from from linux/arch/arm/kernel/swp_emulate.c
		*
		* Copyright (C) 2009 ARM Limited
		* Copyright (c) 2014, NVIDIA CORPORATION. All rights reserved.
		*
		* 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/seq_file.h>
		#include <linux/sched.h>
		#include <linux/syscalls.h>
		#include <linux/perf_event.h>

		#include <asm/opcodes.h>
		#include <asm/traps.h>
		#include <asm/uaccess.h>
		#include <asm/system_misc.h>
		#include <linux/debugfs.h>

		/*
		* 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 pid_t previous_pid;

		u64 swpb_count = 0;
		u64 swp_count = 0;

		/*
		* 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)
		{
		u32 address_reg, destreg, data, type;
		uintptr_t address;
		unsigned int res = 0;
		u32 temp32;
		u8 temp8;

		perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, regs->pc);

		res = arm_check_condition(instr, regs->pstate);
		switch (res) {
		case ARM_OPCODE_CONDTEST_PASS:
		break;
		case ARM_OPCODE_CONDTEST_FAIL:
		/* Condition failed - return to next instruction */
		regs->pc += 4;
		return 0;
		case ARM_OPCODE_CONDTEST_UNCOND:
		/* If unconditional encoding - not a SWP, undef */
		return -EFAULT;
		default:
		return -EINVAL;
		}

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

		address = regs->regs[EXTRACT_REG_NUM(instr, RN_OFFSET)] & 0xffffffff;
		data = regs->regs[EXTRACT_REG_NUM(instr, RT2_OFFSET)];
		destreg = EXTRACT_REG_NUM(instr, RT_OFFSET);

		type = instr & TYPE_SWPB;

		/* 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;
		}
		if (type == TYPE_SWPB) {
		do {
		temp8 = ldax8((u8 *) address);
		} while (stx8((u8 *) address, (u8) data));
		regs->regs[destreg] = temp8;
		regs->pc += 4;
		swpb_count++;
		} else if (address & 0x3) {
		/* SWP to unaligned address not permitted */
		pr_debug("SWP instruction on unaligned pointer!\n");
		return -EFAULT;
		} else {
		do {
		temp32 = ldax32((u32 *) address);
		} while (stlx32((u32 *) address, (u32) data));
		regs->regs[destreg] = temp32;
		regs->pc += 4;
		swp_count++;
		}

		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,
		.pstate_mask = COMPAT_PSR_MODE_MASK \| COMPAT_PSR_T_BIT,
		.pstate_val = COMPAT_PSR_MODE_USR,
		.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)
		{
		struct dentry *dir;
		dir = debugfs_create_dir("swp_emulate", NULL);
		debugfs_create_u64("swp_count", S_IRUGO \| S_IWUSR, dir, &swp_count);
		debugfs_create_u64("swpb_count", S_IRUGO \| S_IWUSR, dir, &swpb_count);

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


		return 0;
		}

		late_initcall(swp_emulation_init);