arch/arm64/kernel/fpsimd.c - arm/linux - Git at Google

 /*
  * FP/SIMD context switching and fault handling
  *
  * Copyright (C) 2012 ARM Ltd.
  * Author: Catalin Marinas <catalin.marinas@arm.com>
  *
  * 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.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #include <linux/bottom_half.h>
 #include <linux/cpu.h>
 #include <linux/cpu_pm.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/sched/signal.h>
 #include <linux/signal.h>

 #include <asm/fpsimd.h>
 #include <asm/cputype.h>
 #include <asm/simd.h>

 #define FPEXC_IOF	(1 << 0)
 #define FPEXC_DZF	(1 << 1)
 #define FPEXC_OFF	(1 << 2)
 #define FPEXC_UFF	(1 << 3)
 #define FPEXC_IXF	(1 << 4)
 #define FPEXC_IDF	(1 << 7)

 /*
  * In order to reduce the number of times the FPSIMD state is needlessly saved
  * and restored, we need to keep track of two things:
  * (a) for each task, we need to remember which CPU was the last one to have
  *     the task's FPSIMD state loaded into its FPSIMD registers;
  * (b) for each CPU, we need to remember which task's userland FPSIMD state has
  *     been loaded into its FPSIMD registers most recently, or whether it has
  *     been used to perform kernel mode NEON in the meantime.
  *
  * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
  * the id of the current CPU every time the state is loaded onto a CPU. For (b),
  * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
  * address of the userland FPSIMD state of the task that was loaded onto the CPU
  * the most recently, or NULL if kernel mode NEON has been performed after that.
  *
  * With this in place, we no longer have to restore the next FPSIMD state right
  * when switching between tasks. Instead, we can defer this check to userland
  * resume, at which time we verify whether the CPU's fpsimd_last_state and the
  * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
  * can omit the FPSIMD restore.
  *
  * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
  * indicate whether or not the userland FPSIMD state of the current task is
  * present in the registers. The flag is set unless the FPSIMD registers of this
  * CPU currently contain the most recent userland FPSIMD state of the current
  * task.
  *
  * In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may
  * save the task's FPSIMD context back to task_struct from softirq context.
  * To prevent this from racing with the manipulation of the task's FPSIMD state
  * from task context and thereby corrupting the state, it is necessary to
  * protect any manipulation of a task's fpsimd_state or TIF_FOREIGN_FPSTATE
  * flag with local_bh_disable() unless softirqs are already masked.
  *
  * For a certain task, the sequence may look something like this:
  * - the task gets scheduled in; if both the task's fpsimd_state.cpu field
  *   contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
  *   variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
  *   cleared, otherwise it is set;
  *
  * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
  *   userland FPSIMD state is copied from memory to the registers, the task's
  *   fpsimd_state.cpu field is set to the id of the current CPU, the current
  *   CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
  *   TIF_FOREIGN_FPSTATE flag is cleared;
  *
  * - the task executes an ordinary syscall; upon return to userland, the
  *   TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
  *   restored;
  *
  * - the task executes a syscall which executes some NEON instructions; this is
  *   preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
  *   register contents to memory, clears the fpsimd_last_state per-cpu variable
  *   and sets the TIF_FOREIGN_FPSTATE flag;
  *
  * - the task gets preempted after kernel_neon_end() is called; as we have not
  *   returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
  *   whatever is in the FPSIMD registers is not saved to memory, but discarded.
  */
 static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);

 /*
  * Trapped FP/ASIMD access.
  */
 void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
 {
 	/* TODO: implement lazy context saving/restoring */
 	WARN_ON(1);
 }

 /*
  * Raise a SIGFPE for the current process.
  */
 void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 {
 	siginfo_t info;
 	unsigned int si_code = 0;

 	if (esr & FPEXC_IOF)
 		si_code = FPE_FLTINV;
 	else if (esr & FPEXC_DZF)
 		si_code = FPE_FLTDIV;
 	else if (esr & FPEXC_OFF)
 		si_code = FPE_FLTOVF;
 	else if (esr & FPEXC_UFF)
 		si_code = FPE_FLTUND;
 	else if (esr & FPEXC_IXF)
 		si_code = FPE_FLTRES;

 	memset(&info, 0, sizeof(info));
 	info.si_signo = SIGFPE;
 	info.si_code = si_code;
 	info.si_addr = (void __user *)instruction_pointer(regs);

 	send_sig_info(SIGFPE, &info, current);
 }

 void fpsimd_thread_switch(struct task_struct *next)
 {
 	if (!system_supports_fpsimd())
 		return;
 	/*
 	 * Save the current FPSIMD state to memory, but only if whatever is in
 	 * the registers is in fact the most recent userland FPSIMD state of
 	 * 'current'.
 	 */
 	if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
 		fpsimd_save_state(&current->thread.fpsimd_state);

 	if (next->mm) {
 		/*
 		 * If we are switching to a task whose most recent userland
 		 * FPSIMD state is already in the registers of *this* cpu,
 		 * we can skip loading the state from memory. Otherwise, set
 		 * the TIF_FOREIGN_FPSTATE flag so the state will be loaded
 		 * upon the next return to userland.
 		 */
 		struct fpsimd_state *st = &next->thread.fpsimd_state;

 		if (__this_cpu_read(fpsimd_last_state) == st
 		    && st->cpu == smp_processor_id())
 			clear_ti_thread_flag(task_thread_info(next),
 					     TIF_FOREIGN_FPSTATE);
 		else
 			set_ti_thread_flag(task_thread_info(next),
 					   TIF_FOREIGN_FPSTATE);
 	}
 }

 void fpsimd_flush_thread(void)
 {
 	if (!system_supports_fpsimd())
 		return;

 	local_bh_disable();

 	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
 	fpsimd_flush_task_state(current);
 	set_thread_flag(TIF_FOREIGN_FPSTATE);

 	local_bh_enable();
 }

 /*
  * Save the userland FPSIMD state of 'current' to memory, but only if the state
  * currently held in the registers does in fact belong to 'current'
  */
 void fpsimd_preserve_current_state(void)
 {
 	if (!system_supports_fpsimd())
 		return;

 	local_bh_disable();

 	if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
 		fpsimd_save_state(&current->thread.fpsimd_state);

 	local_bh_enable();
 }

 /*
  * Load the userland FPSIMD state of 'current' from memory, but only if the
  * FPSIMD state already held in the registers is /not/ the most recent FPSIMD
  * state of 'current'
  */
 void fpsimd_restore_current_state(void)
 {
 	if (!system_supports_fpsimd())
 		return;

 	local_bh_disable();

 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
 		struct fpsimd_state *st = &current->thread.fpsimd_state;

 		fpsimd_load_state(st);
 		__this_cpu_write(fpsimd_last_state, st);
 		st->cpu = smp_processor_id();
 	}

 	local_bh_enable();
 }

 /*
  * Load an updated userland FPSIMD state for 'current' from memory and set the
  * flag that indicates that the FPSIMD register contents are the most recent
  * FPSIMD state of 'current'
  */
 void fpsimd_update_current_state(struct fpsimd_state *state)
 {
 	if (!system_supports_fpsimd())
 		return;

 	local_bh_disable();

 	fpsimd_load_state(state);
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
 		struct fpsimd_state *st = &current->thread.fpsimd_state;

 		__this_cpu_write(fpsimd_last_state, st);
 		st->cpu = smp_processor_id();
 	}

 	local_bh_enable();
 }

 /*
  * Invalidate live CPU copies of task t's FPSIMD state
  */
 void fpsimd_flush_task_state(struct task_struct *t)
 {
 	t->thread.fpsimd_state.cpu = NR_CPUS;
 }

 #ifdef CONFIG_KERNEL_MODE_NEON

 DEFINE_PER_CPU(bool, kernel_neon_busy);
 EXPORT_PER_CPU_SYMBOL(kernel_neon_busy);

 /*
  * Kernel-side NEON support functions
  */

 /*
  * kernel_neon_begin(): obtain the CPU FPSIMD registers for use by the calling
  * context
  *
  * Must not be called unless may_use_simd() returns true.
  * Task context in the FPSIMD registers is saved back to memory as necessary.
  *
  * A matching call to kernel_neon_end() must be made before returning from the
  * calling context.
  *
  * The caller may freely use the FPSIMD registers until kernel_neon_end() is
  * called.
  */
 void kernel_neon_begin(void)
 {
 	if (WARN_ON(!system_supports_fpsimd()))
 		return;

 	BUG_ON(!may_use_simd());

 	local_bh_disable();

 	__this_cpu_write(kernel_neon_busy, true);

 	/* Save unsaved task fpsimd state, if any: */
 	if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
 		fpsimd_save_state(&current->thread.fpsimd_state);

 	/* Invalidate any task state remaining in the fpsimd regs: */
 	__this_cpu_write(fpsimd_last_state, NULL);

 	preempt_disable();

 	local_bh_enable();
 }
 EXPORT_SYMBOL(kernel_neon_begin);

 /*
  * kernel_neon_end(): give the CPU FPSIMD registers back to the current task
  *
  * Must be called from a context in which kernel_neon_begin() was previously
  * called, with no call to kernel_neon_end() in the meantime.
  *
  * The caller must not use the FPSIMD registers after this function is called,
  * unless kernel_neon_begin() is called again in the meantime.
  */
 void kernel_neon_end(void)
 {
 	bool busy;

 	if (!system_supports_fpsimd())
 		return;

 	busy = __this_cpu_xchg(kernel_neon_busy, false);
 	WARN_ON(!busy);	/* No matching kernel_neon_begin()? */

 	preempt_enable();
 }
 EXPORT_SYMBOL(kernel_neon_end);

 #ifdef CONFIG_EFI

 static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state);
 static DEFINE_PER_CPU(bool, efi_fpsimd_state_used);

 /*
  * EFI runtime services support functions
  *
  * The ABI for EFI runtime services allows EFI to use FPSIMD during the call.
  * This means that for EFI (and only for EFI), we have to assume that FPSIMD
  * is always used rather than being an optional accelerator.
  *
  * These functions provide the necessary support for ensuring FPSIMD
  * save/restore in the contexts from which EFI is used.
  *
  * Do not use them for any other purpose -- if tempted to do so, you are
  * either doing something wrong or you need to propose some refactoring.
  */

 /*
  * __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call
  */
 void __efi_fpsimd_begin(void)
 {
 	if (!system_supports_fpsimd())
 		return;

 	WARN_ON(preemptible());

 	if (may_use_simd())
 		kernel_neon_begin();
 	else {
 		fpsimd_save_state(this_cpu_ptr(&efi_fpsimd_state));
 		__this_cpu_write(efi_fpsimd_state_used, true);
 	}
 }

 /*
  * __efi_fpsimd_end(): clean up FPSIMD after an EFI runtime services call
  */
 void __efi_fpsimd_end(void)
 {
 	if (!system_supports_fpsimd())
 		return;

 	if (__this_cpu_xchg(efi_fpsimd_state_used, false))
 		fpsimd_load_state(this_cpu_ptr(&efi_fpsimd_state));
 	else
 		kernel_neon_end();
 }

 #endif /* CONFIG_EFI */

 #endif /* CONFIG_KERNEL_MODE_NEON */

 #ifdef CONFIG_CPU_PM
 static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
 				  unsigned long cmd, void *v)
 {
 	switch (cmd) {
 	case CPU_PM_ENTER:
 		if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
 			fpsimd_save_state(&current->thread.fpsimd_state);
 		this_cpu_write(fpsimd_last_state, NULL);
 		break;
 	case CPU_PM_EXIT:
 		if (current->mm)
 			set_thread_flag(TIF_FOREIGN_FPSTATE);
 		break;
 	case CPU_PM_ENTER_FAILED:
 	default:
 		return NOTIFY_DONE;
 	}
 	return NOTIFY_OK;
 }

 static struct notifier_block fpsimd_cpu_pm_notifier_block = {
 	.notifier_call = fpsimd_cpu_pm_notifier,
 };

 static void __init fpsimd_pm_init(void)
 {
 	cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
 }

 #else
 static inline void fpsimd_pm_init(void) { }
 #endif /* CONFIG_CPU_PM */

 #ifdef CONFIG_HOTPLUG_CPU
 static int fpsimd_cpu_dead(unsigned int cpu)
 {
 	per_cpu(fpsimd_last_state, cpu) = NULL;
 	return 0;
 }

 static inline void fpsimd_hotplug_init(void)
 {
 	cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead",
 				  NULL, fpsimd_cpu_dead);
 }

 #else
 static inline void fpsimd_hotplug_init(void) { }
 #endif

 /*
  * FP/SIMD support code initialisation.
  */
 static int __init fpsimd_init(void)
 {
 	if (elf_hwcap & HWCAP_FP) {
 		fpsimd_pm_init();
 		fpsimd_hotplug_init();
 	} else {
 		pr_notice("Floating-point is not implemented\n");
 	}

 	if (!(elf_hwcap & HWCAP_ASIMD))
 		pr_notice("Advanced SIMD is not implemented\n");

 	return 0;
 }
 core_initcall(fpsimd_init);
	/*
	* FP/SIMD context switching and fault handling
	*
	* Copyright (C) 2012 ARM Ltd.
	* Author: Catalin Marinas <catalin.marinas@arm.com>
	*
	* 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.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#include <linux/bottom_half.h>
	#include <linux/cpu.h>
	#include <linux/cpu_pm.h>
	#include <linux/kernel.h>
	#include <linux/init.h>
	#include <linux/percpu.h>
	#include <linux/preempt.h>
	#include <linux/sched/signal.h>
	#include <linux/signal.h>

	#include <asm/fpsimd.h>
	#include <asm/cputype.h>
	#include <asm/simd.h>

	#define FPEXC_IOF (1 << 0)
	#define FPEXC_DZF (1 << 1)
	#define FPEXC_OFF (1 << 2)
	#define FPEXC_UFF (1 << 3)
	#define FPEXC_IXF (1 << 4)
	#define FPEXC_IDF (1 << 7)

	/*
	* In order to reduce the number of times the FPSIMD state is needlessly saved
	* and restored, we need to keep track of two things:
	* (a) for each task, we need to remember which CPU was the last one to have
	* the task's FPSIMD state loaded into its FPSIMD registers;
	* (b) for each CPU, we need to remember which task's userland FPSIMD state has
	* been loaded into its FPSIMD registers most recently, or whether it has
	* been used to perform kernel mode NEON in the meantime.
	*
	* For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to
	* the id of the current CPU every time the state is loaded onto a CPU. For (b),
	* we add the per-cpu variable 'fpsimd_last_state' (below), which contains the
	* address of the userland FPSIMD state of the task that was loaded onto the CPU
	* the most recently, or NULL if kernel mode NEON has been performed after that.
	*
	* With this in place, we no longer have to restore the next FPSIMD state right
	* when switching between tasks. Instead, we can defer this check to userland
	* resume, at which time we verify whether the CPU's fpsimd_last_state and the
	* task's fpsimd_state.cpu are still mutually in sync. If this is the case, we
	* can omit the FPSIMD restore.
	*
	* As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to
	* indicate whether or not the userland FPSIMD state of the current task is
	* present in the registers. The flag is set unless the FPSIMD registers of this
	* CPU currently contain the most recent userland FPSIMD state of the current
	* task.
	*
	* In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may
	* save the task's FPSIMD context back to task_struct from softirq context.
	* To prevent this from racing with the manipulation of the task's FPSIMD state
	* from task context and thereby corrupting the state, it is necessary to
	* protect any manipulation of a task's fpsimd_state or TIF_FOREIGN_FPSTATE
	* flag with local_bh_disable() unless softirqs are already masked.
	*
	* For a certain task, the sequence may look something like this:
	* - the task gets scheduled in; if both the task's fpsimd_state.cpu field
	* contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu
	* variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is
	* cleared, otherwise it is set;
	*
	* - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's
	* userland FPSIMD state is copied from memory to the registers, the task's
	* fpsimd_state.cpu field is set to the id of the current CPU, the current
	* CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the
	* TIF_FOREIGN_FPSTATE flag is cleared;
	*
	* - the task executes an ordinary syscall; upon return to userland, the
	* TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is
	* restored;
	*
	* - the task executes a syscall which executes some NEON instructions; this is
	* preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD
	* register contents to memory, clears the fpsimd_last_state per-cpu variable
	* and sets the TIF_FOREIGN_FPSTATE flag;
	*
	* - the task gets preempted after kernel_neon_end() is called; as we have not
	* returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so
	* whatever is in the FPSIMD registers is not saved to memory, but discarded.
	*/
	static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state);

	/*
	* Trapped FP/ASIMD access.
	*/
	void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs)
	{
	/* TODO: implement lazy context saving/restoring */
	WARN_ON(1);
	}

	/*
	* Raise a SIGFPE for the current process.
	*/
	void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
	{
	siginfo_t info;
	unsigned int si_code = 0;

	if (esr & FPEXC_IOF)
	si_code = FPE_FLTINV;
	else if (esr & FPEXC_DZF)
	si_code = FPE_FLTDIV;
	else if (esr & FPEXC_OFF)
	si_code = FPE_FLTOVF;
	else if (esr & FPEXC_UFF)
	si_code = FPE_FLTUND;
	else if (esr & FPEXC_IXF)
	si_code = FPE_FLTRES;

	memset(&info, 0, sizeof(info));
	info.si_signo = SIGFPE;
	info.si_code = si_code;
	info.si_addr = (void __user *)instruction_pointer(regs);

	send_sig_info(SIGFPE, &info, current);
	}

	void fpsimd_thread_switch(struct task_struct *next)
	{
	if (!system_supports_fpsimd())
	return;
	/*
	* Save the current FPSIMD state to memory, but only if whatever is in
	* the registers is in fact the most recent userland FPSIMD state of
	* 'current'.
	*/
	if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
	fpsimd_save_state(&current->thread.fpsimd_state);

	if (next->mm) {
	/*
	* If we are switching to a task whose most recent userland
	* FPSIMD state is already in the registers of this cpu,
	* we can skip loading the state from memory. Otherwise, set
	* the TIF_FOREIGN_FPSTATE flag so the state will be loaded
	* upon the next return to userland.
	*/
	struct fpsimd_state *st = &next->thread.fpsimd_state;

	if (__this_cpu_read(fpsimd_last_state) == st
	&& st->cpu == smp_processor_id())
	clear_ti_thread_flag(task_thread_info(next),
	TIF_FOREIGN_FPSTATE);
	else
	set_ti_thread_flag(task_thread_info(next),
	TIF_FOREIGN_FPSTATE);
	}
	}

	void fpsimd_flush_thread(void)
	{
	if (!system_supports_fpsimd())
	return;

	local_bh_disable();

	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
	fpsimd_flush_task_state(current);
	set_thread_flag(TIF_FOREIGN_FPSTATE);

	local_bh_enable();
	}

	/*
	* Save the userland FPSIMD state of 'current' to memory, but only if the state
	* currently held in the registers does in fact belong to 'current'
	*/
	void fpsimd_preserve_current_state(void)
	{
	if (!system_supports_fpsimd())
	return;

	local_bh_disable();

	if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
	fpsimd_save_state(&current->thread.fpsimd_state);

	local_bh_enable();
	}

	/*
	* Load the userland FPSIMD state of 'current' from memory, but only if the
	* FPSIMD state already held in the registers is /not/ the most recent FPSIMD
	* state of 'current'
	*/
	void fpsimd_restore_current_state(void)
	{
	if (!system_supports_fpsimd())
	return;

	local_bh_disable();

	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
	struct fpsimd_state *st = &current->thread.fpsimd_state;

	fpsimd_load_state(st);
	__this_cpu_write(fpsimd_last_state, st);
	st->cpu = smp_processor_id();
	}

	local_bh_enable();
	}

	/*
	* Load an updated userland FPSIMD state for 'current' from memory and set the
	* flag that indicates that the FPSIMD register contents are the most recent
	* FPSIMD state of 'current'
	*/
	void fpsimd_update_current_state(struct fpsimd_state *state)
	{
	if (!system_supports_fpsimd())
	return;

	local_bh_disable();

	fpsimd_load_state(state);
	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
	struct fpsimd_state *st = &current->thread.fpsimd_state;

	__this_cpu_write(fpsimd_last_state, st);
	st->cpu = smp_processor_id();
	}

	local_bh_enable();
	}

	/*
	* Invalidate live CPU copies of task t's FPSIMD state
	*/
	void fpsimd_flush_task_state(struct task_struct *t)
	{
	t->thread.fpsimd_state.cpu = NR_CPUS;
	}

	#ifdef CONFIG_KERNEL_MODE_NEON

	DEFINE_PER_CPU(bool, kernel_neon_busy);
	EXPORT_PER_CPU_SYMBOL(kernel_neon_busy);

	/*
	* Kernel-side NEON support functions
	*/

	/*
	* kernel_neon_begin(): obtain the CPU FPSIMD registers for use by the calling
	* context
	*
	* Must not be called unless may_use_simd() returns true.
	* Task context in the FPSIMD registers is saved back to memory as necessary.
	*
	* A matching call to kernel_neon_end() must be made before returning from the
	* calling context.
	*
	* The caller may freely use the FPSIMD registers until kernel_neon_end() is
	* called.
	*/
	void kernel_neon_begin(void)
	{
	if (WARN_ON(!system_supports_fpsimd()))
	return;

	BUG_ON(!may_use_simd());

	local_bh_disable();

	__this_cpu_write(kernel_neon_busy, true);

	/* Save unsaved task fpsimd state, if any: */
	if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE))
	fpsimd_save_state(&current->thread.fpsimd_state);

	/* Invalidate any task state remaining in the fpsimd regs: */
	__this_cpu_write(fpsimd_last_state, NULL);

	preempt_disable();

	local_bh_enable();
	}
	EXPORT_SYMBOL(kernel_neon_begin);

	/*
	* kernel_neon_end(): give the CPU FPSIMD registers back to the current task
	*
	* Must be called from a context in which kernel_neon_begin() was previously
	* called, with no call to kernel_neon_end() in the meantime.
	*
	* The caller must not use the FPSIMD registers after this function is called,
	* unless kernel_neon_begin() is called again in the meantime.
	*/
	void kernel_neon_end(void)
	{
	bool busy;

	if (!system_supports_fpsimd())
	return;

	busy = __this_cpu_xchg(kernel_neon_busy, false);
	WARN_ON(!busy); /* No matching kernel_neon_begin()? */

	preempt_enable();
	}
	EXPORT_SYMBOL(kernel_neon_end);

	#ifdef CONFIG_EFI

	static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state);
	static DEFINE_PER_CPU(bool, efi_fpsimd_state_used);

	/*
	* EFI runtime services support functions
	*
	* The ABI for EFI runtime services allows EFI to use FPSIMD during the call.
	* This means that for EFI (and only for EFI), we have to assume that FPSIMD
	* is always used rather than being an optional accelerator.
	*
	* These functions provide the necessary support for ensuring FPSIMD
	* save/restore in the contexts from which EFI is used.
	*
	* Do not use them for any other purpose -- if tempted to do so, you are
	* either doing something wrong or you need to propose some refactoring.
	*/

	/*
	* __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call
	*/
	void __efi_fpsimd_begin(void)
	{
	if (!system_supports_fpsimd())
	return;

	WARN_ON(preemptible());

	if (may_use_simd())
	kernel_neon_begin();
	else {
	fpsimd_save_state(this_cpu_ptr(&efi_fpsimd_state));
	__this_cpu_write(efi_fpsimd_state_used, true);
	}
	}

	/*
	* __efi_fpsimd_end(): clean up FPSIMD after an EFI runtime services call
	*/
	void __efi_fpsimd_end(void)
	{
	if (!system_supports_fpsimd())
	return;

	if (__this_cpu_xchg(efi_fpsimd_state_used, false))
	fpsimd_load_state(this_cpu_ptr(&efi_fpsimd_state));
	else
	kernel_neon_end();
	}

	#endif /* CONFIG_EFI */

	#endif /* CONFIG_KERNEL_MODE_NEON */

	#ifdef CONFIG_CPU_PM
	static int fpsimd_cpu_pm_notifier(struct notifier_block *self,
	unsigned long cmd, void *v)
	{
	switch (cmd) {
	case CPU_PM_ENTER:
	if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE))
	fpsimd_save_state(&current->thread.fpsimd_state);
	this_cpu_write(fpsimd_last_state, NULL);
	break;
	case CPU_PM_EXIT:
	if (current->mm)
	set_thread_flag(TIF_FOREIGN_FPSTATE);
	break;
	case CPU_PM_ENTER_FAILED:
	default:
	return NOTIFY_DONE;
	}
	return NOTIFY_OK;
	}

	static struct notifier_block fpsimd_cpu_pm_notifier_block = {
	.notifier_call = fpsimd_cpu_pm_notifier,
	};

	static void __init fpsimd_pm_init(void)
	{
	cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block);
	}

	#else
	static inline void fpsimd_pm_init(void) { }
	#endif /* CONFIG_CPU_PM */

	#ifdef CONFIG_HOTPLUG_CPU
	static int fpsimd_cpu_dead(unsigned int cpu)
	{
	per_cpu(fpsimd_last_state, cpu) = NULL;
	return 0;
	}

	static inline void fpsimd_hotplug_init(void)
	{
	cpuhp_setup_state_nocalls(CPUHP_ARM64_FPSIMD_DEAD, "arm64/fpsimd:dead",
	NULL, fpsimd_cpu_dead);
	}

	#else
	static inline void fpsimd_hotplug_init(void) { }
	#endif

	/*
	* FP/SIMD support code initialisation.
	*/
	static int __init fpsimd_init(void)
	{
	if (elf_hwcap & HWCAP_FP) {
	fpsimd_pm_init();
	fpsimd_hotplug_init();
	} else {
	pr_notice("Floating-point is not implemented\n");
	}

	if (!(elf_hwcap & HWCAP_ASIMD))
	pr_notice("Advanced SIMD is not implemented\n");

	return 0;
	}
	core_initcall(fpsimd_init);