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Commit c852f320 authored by Punit Agrawal's avatar Punit Agrawal Committed by Will Deacon
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arm64: Emulate CP15 Barrier instructions 



The CP15 barrier instructions (CP15ISB, CP15DSB and CP15DMB) are
deprecated in the ARMv7 architecture, superseded by ISB, DSB and DMB
instructions respectively. Some implementations may provide the
ability to disable the CP15 barriers by disabling the CP15BEN bit in
SCTLR_EL1. If not enabled, the encodings for these instructions become
undefined.

To support legacy software using these instructions, this patch
register hooks to -
* emulate CP15 barriers and warn the user about their use
* toggle CP15BEN in SCTLR_EL1

Signed-off-by: default avatarPunit Agrawal <punit.agrawal@arm.com>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent bd35a4ad

Documentation/arm64/legacy_instructions.txt

+5 −0
Original line number Diff line number Diff line
@@ -38,3 +38,8 @@ Supported legacy instructions 
Node: /proc/sys/abi/swp

Status: Obsolete

Default: Undef (0)



* CP15 Barriers

Node: /proc/sys/abi/cp15_barrier

Status: Deprecated

Default: Emulate (1)

arch/arm64/Kconfig

+15 −0
Original line number Diff line number Diff line
@@ -201,6 +201,21 @@ config SWP_EMULATION 


	  If unsure, say Y



config CP15_BARRIER_EMULATION

	bool "Emulate CP15 Barrier instructions"

	help

	  The CP15 barrier instructions - CP15ISB, CP15DSB, and

	  CP15DMB - are deprecated in ARMv8 (and ARMv7). It is

	  strongly recommended to use the ISB, DSB, and DMB

	  instructions instead.



	  Say Y here to enable software emulation of these

	  instructions for AArch32 userspace code. When this option is

	  enabled, CP15 barrier usage is traced which can help

	  identify software that needs updating.



	  If unsure, say Y



endif



endmenu

arch/arm64/include/asm/insn.h

+2 −0
Original line number Diff line number Diff line
@@ -362,6 +362,8 @@ bool aarch32_insn_is_wide(u32 insn); 
#define A32_RT2_OFFSET	 0



u32 aarch32_insn_extract_reg_num(u32 insn, int offset);

u32 aarch32_insn_mcr_extract_opc2(u32 insn);

u32 aarch32_insn_mcr_extract_crm(u32 insn);

#endif /* __ASSEMBLY__ */



#endif	/* __ASM_INSN_H */

arch/arm64/kernel/armv8_deprecated.c

+131 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
 * published by the Free Software Foundation.

 */



#include <linux/cpu.h>

#include <linux/init.h>

#include <linux/list.h>

#include <linux/perf_event.h>
@@ -391,6 +392,133 @@ static struct insn_emulation_ops swp_ops = { 
	.set_hw_mode = NULL,

};



static int cp15barrier_handler(struct pt_regs *regs, u32 instr)

{

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



	switch (arm_check_condition(instr, regs->pstate)) {

	case ARM_OPCODE_CONDTEST_PASS:

		break;

	case ARM_OPCODE_CONDTEST_FAIL:

		/* Condition failed - return to next instruction */

		goto ret;

	case ARM_OPCODE_CONDTEST_UNCOND:

		/* If unconditional encoding - not a barrier instruction */

		return -EFAULT;

	default:

		return -EINVAL;

	}



	switch (aarch32_insn_mcr_extract_crm(instr)) {

	case 10:

		/*

		 * dmb - mcr p15, 0, Rt, c7, c10, 5

		 * dsb - mcr p15, 0, Rt, c7, c10, 4

		 */

		if (aarch32_insn_mcr_extract_opc2(instr) == 5)

			dmb(sy);

		else

			dsb(sy);

		break;

	case 5:

		/*

		 * isb - mcr p15, 0, Rt, c7, c5, 4

		 *

		 * Taking an exception or returning from one acts as an

		 * instruction barrier. So no explicit barrier needed here.

		 */

		break;

	}



ret:

	pr_warn_ratelimited("\"%s\" (%ld) uses deprecated CP15 Barrier instruction at 0x%llx\n",

			current->comm, (unsigned long)current->pid, regs->pc);



	regs->pc += 4;

	return 0;

}



#define SCTLR_EL1_CP15BEN (1 << 5)



static inline void config_sctlr_el1(u32 clear, u32 set)

{

	u32 val;



	asm volatile("mrs %0, sctlr_el1" : "=r" (val));

	val &= ~clear;

	val |= set;

	asm volatile("msr sctlr_el1, %0" : : "r" (val));

}



static void enable_cp15_ben(void *info)

{

	config_sctlr_el1(0, SCTLR_EL1_CP15BEN);

}



static void disable_cp15_ben(void *info)

{

	config_sctlr_el1(SCTLR_EL1_CP15BEN, 0);

}



static int cpu_hotplug_notify(struct notifier_block *b,

			      unsigned long action, void *hcpu)

{

	switch (action) {

	case CPU_STARTING:

	case CPU_STARTING_FROZEN:

		enable_cp15_ben(NULL);

		return NOTIFY_DONE;

	case CPU_DYING:

	case CPU_DYING_FROZEN:

		disable_cp15_ben(NULL);

		return NOTIFY_DONE;

	}



	return NOTIFY_OK;

}



static struct notifier_block cpu_hotplug_notifier = {

	.notifier_call = cpu_hotplug_notify,

};



static int cp15_barrier_set_hw_mode(bool enable)

{

	if (enable) {

		register_cpu_notifier(&cpu_hotplug_notifier);

		on_each_cpu(enable_cp15_ben, NULL, true);

	} else {

		unregister_cpu_notifier(&cpu_hotplug_notifier);

		on_each_cpu(disable_cp15_ben, NULL, true);

	}



	return true;

}



static struct undef_hook cp15_barrier_hooks[] = {

	{

		.instr_mask	= 0x0fff0fdf,

		.instr_val	= 0x0e070f9a,

		.pstate_mask	= COMPAT_PSR_MODE_MASK,

		.pstate_val	= COMPAT_PSR_MODE_USR,

		.fn		= cp15barrier_handler,

	},

	{

		.instr_mask	= 0x0fff0fff,

		.instr_val	= 0x0e070f95,

		.pstate_mask	= COMPAT_PSR_MODE_MASK,

		.pstate_val	= COMPAT_PSR_MODE_USR,

		.fn		= cp15barrier_handler,

	},

	{ }

};



static struct insn_emulation_ops cp15_barrier_ops = {

	.name = "cp15_barrier",

	.status = INSN_DEPRECATED,

	.hooks = cp15_barrier_hooks,

	.set_hw_mode = cp15_barrier_set_hw_mode,

};



/*

 * Invoked as late_initcall, since not needed before init spawned.

 */
@@ -399,6 +527,9 @@ static int __init armv8_deprecated_init(void) 
	if (IS_ENABLED(CONFIG_SWP_EMULATION))

		register_insn_emulation(&swp_ops);



	if (IS_ENABLED(CONFIG_CP15_BARRIER_EMULATION))

		register_insn_emulation(&cp15_barrier_ops);



	register_insn_emulation_sysctl(ctl_abi);



	return 0;

arch/arm64/kernel/insn.c

+13 −0
Original line number Diff line number Diff line
@@ -972,3 +972,16 @@ u32 aarch32_insn_extract_reg_num(u32 insn, int offset) 
{

	return (insn & (0xf << offset)) >> offset;

}



#define OPC2_MASK	0x7

#define OPC2_OFFSET	5

u32 aarch32_insn_mcr_extract_opc2(u32 insn)

{

	return (insn & (OPC2_MASK << OPC2_OFFSET)) >> OPC2_OFFSET;

}



#define CRM_MASK	0xf

u32 aarch32_insn_mcr_extract_crm(u32 insn)

{

	return insn & CRM_MASK;

}