LoongArch: Add process management

Add process management support for LoongArch, including: thread info
definition, context switch and process tracing.

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

8 files changed, 810 insertions, 0 deletions

diff --git a/arch/loongarch/include/asm/fpu.h b/arch/loongarch/include/asm/fpu.h
new file mode 100644
index 000000000000..358b254d9c1d
--- /dev/null
+++ b/arch/loongarch/include/asm/fpu.h
@@ -0,0 +1,129 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Author: Huacai Chen <chenhuacai@loongson.cn>
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_FPU_H
+#define _ASM_FPU_H
+
+#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+#include <linux/ptrace.h>
+#include <linux/thread_info.h>
+#include <linux/bitops.h>
+
+#include <asm/cpu.h>
+#include <asm/cpu-features.h>
+#include <asm/current.h>
+#include <asm/loongarch.h>
+#include <asm/processor.h>
+#include <asm/ptrace.h>
+
+struct sigcontext;
+
+extern void _init_fpu(unsigned int);
+extern void _save_fp(struct loongarch_fpu *);
+extern void _restore_fp(struct loongarch_fpu *);
+
+/*
+ * Mask the FCSR Cause bits according to the Enable bits, observing
+ * that Unimplemented is always enabled.
+ */
+static inline unsigned long mask_fcsr_x(unsigned long fcsr)
+{
+	return fcsr & ((fcsr & FPU_CSR_ALL_E) <<
+			(ffs(FPU_CSR_ALL_X) - ffs(FPU_CSR_ALL_E)));
+}
+
+static inline int is_fp_enabled(void)
+{
+	return (csr_read32(LOONGARCH_CSR_EUEN) & CSR_EUEN_FPEN) ?
+		1 : 0;
+}
+
+#define enable_fpu()		set_csr_euen(CSR_EUEN_FPEN)
+
+#define disable_fpu()		clear_csr_euen(CSR_EUEN_FPEN)
+
+#define clear_fpu_owner()	clear_thread_flag(TIF_USEDFPU)
+
+static inline int is_fpu_owner(void)
+{
+	return test_thread_flag(TIF_USEDFPU);
+}
+
+static inline void __own_fpu(void)
+{
+	enable_fpu();
+	set_thread_flag(TIF_USEDFPU);
+	KSTK_EUEN(current) |= CSR_EUEN_FPEN;
+}
+
+static inline void own_fpu_inatomic(int restore)
+{
+	if (cpu_has_fpu && !is_fpu_owner()) {
+		__own_fpu();
+		if (restore)
+			_restore_fp(&current->thread.fpu);
+	}
+}
+
+static inline void own_fpu(int restore)
+{
+	preempt_disable();
+	own_fpu_inatomic(restore);
+	preempt_enable();
+}
+
+static inline void lose_fpu_inatomic(int save, struct task_struct *tsk)
+{
+	if (is_fpu_owner()) {
+		if (save)
+			_save_fp(&tsk->thread.fpu);
+		disable_fpu();
+		clear_tsk_thread_flag(tsk, TIF_USEDFPU);
+	}
+	KSTK_EUEN(tsk) &= ~(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
+}
+
+static inline void lose_fpu(int save)
+{
+	preempt_disable();
+	lose_fpu_inatomic(save, current);
+	preempt_enable();
+}
+
+static inline void init_fpu(void)
+{
+	unsigned int fcsr = current->thread.fpu.fcsr;
+
+	__own_fpu();
+	_init_fpu(fcsr);
+	set_used_math();
+}
+
+static inline void save_fp(struct task_struct *tsk)
+{
+	if (cpu_has_fpu)
+		_save_fp(&tsk->thread.fpu);
+}
+
+static inline void restore_fp(struct task_struct *tsk)
+{
+	if (cpu_has_fpu)
+		_restore_fp(&tsk->thread.fpu);
+}
+
+static inline union fpureg *get_fpu_regs(struct task_struct *tsk)
+{
+	if (tsk == current) {
+		preempt_disable();
+		if (is_fpu_owner())
+			_save_fp(&current->thread.fpu);
+		preempt_enable();
+	}
+
+	return tsk->thread.fpu.fpr;
+}
+
+#endif /* _ASM_FPU_H */
diff --git a/arch/loongarch/include/asm/idle.h b/arch/loongarch/include/asm/idle.h
new file mode 100644
index 000000000000..f7f2b7dbf958
--- /dev/null
+++ b/arch/loongarch/include/asm/idle.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_IDLE_H
+#define __ASM_IDLE_H
+
+#include <linux/linkage.h>
+
+extern asmlinkage void __arch_cpu_idle(void);
+
+#endif /* __ASM_IDLE_H  */
diff --git a/arch/loongarch/include/asm/mmu.h b/arch/loongarch/include/asm/mmu.h
new file mode 100644
index 000000000000..0cc2d0803537
--- /dev/null
+++ b/arch/loongarch/include/asm/mmu.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef __ASM_MMU_H
+#define __ASM_MMU_H
+
+#include <linux/atomic.h>
+#include <linux/spinlock.h>
+
+typedef struct {
+	u64 asid[NR_CPUS];
+	void *vdso;
+} mm_context_t;
+
+#endif /* __ASM_MMU_H */
diff --git a/arch/loongarch/include/asm/mmu_context.h b/arch/loongarch/include/asm/mmu_context.h
new file mode 100644
index 000000000000..9f97c3453b9c
--- /dev/null
+++ b/arch/loongarch/include/asm/mmu_context.h
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Switch a MMU context.
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_MMU_CONTEXT_H
+#define _ASM_MMU_CONTEXT_H
+
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/mm_types.h>
+#include <linux/smp.h>
+#include <linux/slab.h>
+
+#include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
+#include <asm-generic/mm_hooks.h>
+
+/*
+ *  All unused by hardware upper bits will be considered
+ *  as a software asid extension.
+ */
+static inline u64 asid_version_mask(unsigned int cpu)
+{
+	return ~(u64)(cpu_asid_mask(&cpu_data[cpu]));
+}
+
+static inline u64 asid_first_version(unsigned int cpu)
+{
+	return cpu_asid_mask(&cpu_data[cpu]) + 1;
+}
+
+#define cpu_context(cpu, mm)	((mm)->context.asid[cpu])
+#define asid_cache(cpu)		(cpu_data[cpu].asid_cache)
+#define cpu_asid(cpu, mm)	(cpu_context((cpu), (mm)) & cpu_asid_mask(&cpu_data[cpu]))
+
+static inline int asid_valid(struct mm_struct *mm, unsigned int cpu)
+{
+	if ((cpu_context(cpu, mm) ^ asid_cache(cpu)) & asid_version_mask(cpu))
+		return 0;
+
+	return 1;
+}
+
+static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
+{
+}
+
+/* Normal, classic get_new_mmu_context */
+static inline void
+get_new_mmu_context(struct mm_struct *mm, unsigned long cpu)
+{
+	u64 asid = asid_cache(cpu);
+
+	if (!((++asid) & cpu_asid_mask(&cpu_data[cpu])))
+		local_flush_tlb_user();	/* start new asid cycle */
+
+	cpu_context(cpu, mm) = asid_cache(cpu) = asid;
+}
+
+/*
+ * Initialize the context related info for a new mm_struct
+ * instance.
+ */
+static inline int
+init_new_context(struct task_struct *tsk, struct mm_struct *mm)
+{
+	int i;
+
+	for_each_possible_cpu(i)
+		cpu_context(i, mm) = 0;
+
+	return 0;
+}
+
+static inline void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
+				      struct task_struct *tsk)
+{
+	unsigned int cpu = smp_processor_id();
+
+	/* Check if our ASID is of an older version and thus invalid */
+	if (!asid_valid(next, cpu))
+		get_new_mmu_context(next, cpu);
+
+	write_csr_asid(cpu_asid(cpu, next));
+
+	if (next != &init_mm)
+		csr_write64((unsigned long)next->pgd, LOONGARCH_CSR_PGDL);
+	else
+		csr_write64((unsigned long)invalid_pg_dir, LOONGARCH_CSR_PGDL);
+
+	/*
+	 * Mark current->active_mm as not "active" anymore.
+	 * We don't want to mislead possible IPI tlb flush routines.
+	 */
+	cpumask_set_cpu(cpu, mm_cpumask(next));
+}
+
+#define switch_mm_irqs_off switch_mm_irqs_off
+
+static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
+			     struct task_struct *tsk)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	switch_mm_irqs_off(prev, next, tsk);
+	local_irq_restore(flags);
+}
+
+/*
+ * Destroy context related info for an mm_struct that is about
+ * to be put to rest.
+ */
+static inline void destroy_context(struct mm_struct *mm)
+{
+}
+
+#define activate_mm(prev, next)	switch_mm(prev, next, current)
+#define deactivate_mm(task, mm)	do { } while (0)
+
+/*
+ * If mm is currently active, we can't really drop it.
+ * Instead, we will get a new one for it.
+ */
+static inline void
+drop_mmu_context(struct mm_struct *mm, unsigned int cpu)
+{
+	int asid;
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	asid = read_csr_asid() & cpu_asid_mask(&current_cpu_data);
+
+	if (asid == cpu_asid(cpu, mm)) {
+		if (!current->mm || (current->mm == mm)) {
+			get_new_mmu_context(mm, cpu);
+			write_csr_asid(cpu_asid(cpu, mm));
+			goto out;
+		}
+	}
+
+	/* Will get a new context next time */
+	cpu_context(cpu, mm) = 0;
+	cpumask_clear_cpu(cpu, mm_cpumask(mm));
+out:
+	local_irq_restore(flags);
+}
+
+#endif /* _ASM_MMU_CONTEXT_H */
diff --git a/arch/loongarch/include/asm/processor.h b/arch/loongarch/include/asm/processor.h
new file mode 100644
index 000000000000..1d63c934b289
--- /dev/null
+++ b/arch/loongarch/include/asm/processor.h
@@ -0,0 +1,209 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_PROCESSOR_H
+#define _ASM_PROCESSOR_H
+
+#include <linux/atomic.h>
+#include <linux/cpumask.h>
+#include <linux/sizes.h>
+
+#include <asm/cpu.h>
+#include <asm/cpu-info.h>
+#include <asm/loongarch.h>
+#include <asm/vdso/processor.h>
+#include <uapi/asm/ptrace.h>
+#include <uapi/asm/sigcontext.h>
+
+#ifdef CONFIG_32BIT
+
+#define TASK_SIZE	0x80000000UL
+#define TASK_SIZE_MIN	TASK_SIZE
+#define STACK_TOP_MAX	TASK_SIZE
+
+#define TASK_IS_32BIT_ADDR 1
+
+#endif
+
+#ifdef CONFIG_64BIT
+
+#define TASK_SIZE32	0x100000000UL
+#define TASK_SIZE64     (0x1UL << ((cpu_vabits > VA_BITS) ? VA_BITS : cpu_vabits))
+
+#define TASK_SIZE	(test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
+#define TASK_SIZE_MIN	TASK_SIZE32
+#define STACK_TOP_MAX	TASK_SIZE64
+
+#define TASK_SIZE_OF(tsk)						\
+	(test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
+
+#define TASK_IS_32BIT_ADDR test_thread_flag(TIF_32BIT_ADDR)
+
+#endif
+
+#define VDSO_RANDOMIZE_SIZE	(TASK_IS_32BIT_ADDR ? SZ_1M : SZ_64M)
+
+unsigned long stack_top(void);
+#define STACK_TOP stack_top()
+
+/*
+ * This decides where the kernel will search for a free chunk of vm
+ * space during mmap's.
+ */
+#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE / 3)
+
+#define FPU_REG_WIDTH		256
+#define FPU_ALIGN		__attribute__((aligned(32)))
+
+union fpureg {
+	__u32	val32[FPU_REG_WIDTH / 32];
+	__u64	val64[FPU_REG_WIDTH / 64];
+};
+
+#define FPR_IDX(width, idx)	(idx)
+
+#define BUILD_FPR_ACCESS(width) \
+static inline u##width get_fpr##width(union fpureg *fpr, unsigned idx)	\
+{									\
+	return fpr->val##width[FPR_IDX(width, idx)];			\
+}									\
+									\
+static inline void set_fpr##width(union fpureg *fpr, unsigned int idx,	\
+				  u##width val)				\
+{									\
+	fpr->val##width[FPR_IDX(width, idx)] = val;			\
+}
+
+BUILD_FPR_ACCESS(32)
+BUILD_FPR_ACCESS(64)
+
+struct loongarch_fpu {
+	unsigned int	fcsr;
+	unsigned int	vcsr;
+	uint64_t	fcc;	/* 8x8 */
+	union fpureg	fpr[NUM_FPU_REGS];
+};
+
+#define INIT_CPUMASK { \
+	{0,} \
+}
+
+#define ARCH_MIN_TASKALIGN	32
+
+struct loongarch_vdso_info;
+
+/*
+ * If you change thread_struct remember to change the #defines below too!
+ */
+struct thread_struct {
+	/* Main processor registers. */
+	unsigned long reg01, reg03, reg22; /* ra sp fp */
+	unsigned long reg23, reg24, reg25, reg26; /* s0-s3 */
+	unsigned long reg27, reg28, reg29, reg30, reg31; /* s4-s8 */
+
+	/* CSR registers */
+	unsigned long csr_prmd;
+	unsigned long csr_crmd;
+	unsigned long csr_euen;
+	unsigned long csr_ecfg;
+	unsigned long csr_badvaddr;	/* Last user fault */
+
+	/* Scratch registers */
+	unsigned long scr0;
+	unsigned long scr1;
+	unsigned long scr2;
+	unsigned long scr3;
+
+	/* Eflags register */
+	unsigned long eflags;
+
+	/* Other stuff associated with the thread. */
+	unsigned long trap_nr;
+	unsigned long error_code;
+	struct loongarch_vdso_info *vdso;
+
+	/*
+	 * FPU & vector registers, must be at last because
+	 * they are conditionally copied at fork().
+	 */
+	struct loongarch_fpu fpu FPU_ALIGN;
+};
+
+#define INIT_THREAD  {						\
+	/*							\
+	 * Main processor registers				\
+	 */							\
+	.reg01			= 0,				\
+	.reg03			= 0,				\
+	.reg22			= 0,				\
+	.reg23			= 0,				\
+	.reg24			= 0,				\
+	.reg25			= 0,				\
+	.reg26			= 0,				\
+	.reg27			= 0,				\
+	.reg28			= 0,				\
+	.reg29			= 0,				\
+	.reg30			= 0,				\
+	.reg31			= 0,				\
+	.csr_crmd		= 0,				\
+	.csr_prmd		= 0,				\
+	.csr_euen		= 0,				\
+	.csr_ecfg		= 0,				\
+	.csr_badvaddr		= 0,				\
+	/*							\
+	 * Other stuff associated with the process		\
+	 */							\
+	.trap_nr		= 0,				\
+	.error_code		= 0,				\
+	/*							\
+	 * FPU & vector registers				\
+	 */							\
+	.fpu			= {				\
+		.fcsr		= 0,				\
+		.vcsr		= 0,				\
+		.fcc		= 0,				\
+		.fpr		= {{{0,},},},			\
+	},							\
+}
+
+struct task_struct;
+
+/* Free all resources held by a thread. */
+#define release_thread(thread) do { } while (0)
+
+enum idle_boot_override {IDLE_NO_OVERRIDE = 0, IDLE_HALT, IDLE_NOMWAIT, IDLE_POLL};
+
+extern unsigned long		boot_option_idle_override;
+/*
+ * Do necessary setup to start up a newly executed thread.
+ */
+extern void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp);
+
+static inline void flush_thread(void)
+{
+}
+
+unsigned long __get_wchan(struct task_struct *p);
+
+#define __KSTK_TOS(tsk) ((unsigned long)task_stack_page(tsk) + \
+			 THREAD_SIZE - 32 - sizeof(struct pt_regs))
+#define task_pt_regs(tsk) ((struct pt_regs *)__KSTK_TOS(tsk))
+#define KSTK_EIP(tsk) (task_pt_regs(tsk)->csr_era)
+#define KSTK_ESP(tsk) (task_pt_regs(tsk)->regs[3])
+#define KSTK_EUEN(tsk) (task_pt_regs(tsk)->csr_euen)
+#define KSTK_ECFG(tsk) (task_pt_regs(tsk)->csr_ecfg)
+
+#define return_address() ({__asm__ __volatile__("":::"$1"); __builtin_return_address(0);})
+
+#ifdef CONFIG_CPU_HAS_PREFETCH
+
+#define ARCH_HAS_PREFETCH
+#define prefetch(x) __builtin_prefetch((x), 0, 1)
+
+#define ARCH_HAS_PREFETCHW
+#define prefetchw(x) __builtin_prefetch((x), 1, 1)
+
+#endif
+
+#endif /* _ASM_PROCESSOR_H */
diff --git a/arch/loongarch/include/asm/ptrace.h b/arch/loongarch/include/asm/ptrace.h
new file mode 100644
index 000000000000..17838c6b7ccd
--- /dev/null
+++ b/arch/loongarch/include/asm/ptrace.h
@@ -0,0 +1,152 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_PTRACE_H
+#define _ASM_PTRACE_H
+
+#include <asm/page.h>
+#include <asm/thread_info.h>
+#include <uapi/asm/ptrace.h>
+
+/*
+ * This struct defines the way the registers are stored on the stack during
+ * a system call/exception. If you add a register here, please also add it to
+ * regoffset_table[] in arch/loongarch/kernel/ptrace.c.
+ */
+struct pt_regs {
+	/* Main processor registers. */
+	unsigned long regs[32];
+
+	/* Original syscall arg0. */
+	unsigned long orig_a0;
+
+	/* Special CSR registers. */
+	unsigned long csr_era;
+	unsigned long csr_badvaddr;
+	unsigned long csr_crmd;
+	unsigned long csr_prmd;
+	unsigned long csr_euen;
+	unsigned long csr_ecfg;
+	unsigned long csr_estat;
+	unsigned long __last[0];
+} __aligned(8);
+
+static inline int regs_irqs_disabled(struct pt_regs *regs)
+{
+	return arch_irqs_disabled_flags(regs->csr_prmd);
+}
+
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->regs[3];
+}
+
+/*
+ * Don't use asm-generic/ptrace.h it defines FP accessors that don't make
+ * sense on LoongArch.  We rather want an error if they get invoked.
+ */
+
+static inline void instruction_pointer_set(struct pt_regs *regs, unsigned long val)
+{
+	regs->csr_era = val;
+}
+
+/* Query offset/name of register from its name/offset */
+extern int regs_query_register_offset(const char *name);
+#define MAX_REG_OFFSET (offsetof(struct pt_regs, __last))
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:       pt_regs from which register value is gotten.
+ * @offset:     offset number of the register.
+ *
+ * regs_get_register returns the value of a register. The @offset is the
+ * offset of the register in struct pt_regs address which specified by @regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs, unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:       pt_regs which contains kernel stack pointer.
+ * @addr:       address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+static inline int regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
+{
+	return ((addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:       pt_regs which contains kernel stack pointer.
+ * @n:          stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
+struct task_struct;
+
+/*
+ * Does the process account for user or for system time?
+ */
+#define user_mode(regs) (((regs)->csr_prmd & PLV_MASK) == PLV_USER)
+
+static inline long regs_return_value(struct pt_regs *regs)
+{
+	return regs->regs[4];
+}
+
+#define instruction_pointer(regs) ((regs)->csr_era)
+#define profile_pc(regs) instruction_pointer(regs)
+
+extern void die(const char *, struct pt_regs *) __noreturn;
+
+static inline void die_if_kernel(const char *str, struct pt_regs *regs)
+{
+	if (unlikely(!user_mode(regs)))
+		die(str, regs);
+}
+
+#define current_pt_regs()						\
+({									\
+	unsigned long sp = (unsigned long)__builtin_frame_address(0);	\
+	(struct pt_regs *)((sp | (THREAD_SIZE - 1)) + 1 - 32) - 1;	\
+})
+
+/* Helpers for working with the user stack pointer */
+
+static inline unsigned long user_stack_pointer(struct pt_regs *regs)
+{
+	return regs->regs[3];
+}
+
+static inline void user_stack_pointer_set(struct pt_regs *regs,
+	unsigned long val)
+{
+	regs->regs[3] = val;
+}
+
+#endif /* _ASM_PTRACE_H */
diff --git a/arch/loongarch/include/asm/switch_to.h b/arch/loongarch/include/asm/switch_to.h
new file mode 100644
index 000000000000..2a8d04375574
--- /dev/null
+++ b/arch/loongarch/include/asm/switch_to.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_SWITCH_TO_H
+#define _ASM_SWITCH_TO_H
+
+#include <asm/cpu-features.h>
+#include <asm/fpu.h>
+
+struct task_struct;
+
+/**
+ * __switch_to - switch execution of a task
+ * @prev:	The task previously executed.
+ * @next:	The task to begin executing.
+ * @next_ti:	task_thread_info(next).
+ *
+ * This function is used whilst scheduling to save the context of prev & load
+ * the context of next. Returns prev.
+ */
+extern asmlinkage struct task_struct *__switch_to(struct task_struct *prev,
+			struct task_struct *next, struct thread_info *next_ti);
+
+/*
+ * For newly created kernel threads switch_to() will return to
+ * ret_from_kernel_thread, newly created user threads to ret_from_fork.
+ * That is, everything following __switch_to() will be skipped for new threads.
+ * So everything that matters to new threads should be placed before __switch_to().
+ */
+#define switch_to(prev, next, last)					\
+do {									\
+	lose_fpu_inatomic(1, prev);					\
+	(last) = __switch_to(prev, next, task_thread_info(next));	\
+} while (0)
+
+#endif /* _ASM_SWITCH_TO_H */
diff --git a/arch/loongarch/include/asm/thread_info.h b/arch/loongarch/include/asm/thread_info.h
new file mode 100644
index 000000000000..99beb11c2fa8
--- /dev/null
+++ b/arch/loongarch/include/asm/thread_info.h
@@ -0,0 +1,106 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * thread_info.h: LoongArch low-level thread information
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+
+#ifndef _ASM_THREAD_INFO_H
+#define _ASM_THREAD_INFO_H
+
+#ifdef __KERNEL__
+
+#ifndef __ASSEMBLY__
+
+#include <asm/processor.h>
+
+/*
+ * low level task data that entry.S needs immediate access to
+ * - this struct should fit entirely inside of one cache line
+ * - this struct shares the supervisor stack pages
+ * - if the contents of this structure are changed, the assembly constants
+ *   must also be changed
+ */
+struct thread_info {
+	struct task_struct	*task;		/* main task structure */
+	unsigned long		flags;		/* low level flags */
+	unsigned long		tp_value;	/* thread pointer */
+	__u32			cpu;		/* current CPU */
+	int			preempt_count;	/* 0 => preemptible, <0 => BUG */
+	struct pt_regs		*regs;
+	unsigned long		syscall;	/* syscall number */
+	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
+};
+
+/*
+ * macros/functions for gaining access to the thread information structure
+ */
+#define INIT_THREAD_INFO(tsk)			\
+{						\
+	.task		= &tsk,			\
+	.flags		= 0,			\
+	.cpu		= 0,			\
+	.preempt_count	= INIT_PREEMPT_COUNT,	\
+}
+
+/* How to get the thread information struct from C. */
+register struct thread_info *__current_thread_info __asm__("$r2");
+
+static inline struct thread_info *current_thread_info(void)
+{
+	return __current_thread_info;
+}
+
+register unsigned long current_stack_pointer __asm__("$r3");
+
+#endif /* !__ASSEMBLY__ */
+
+/* thread information allocation */
+#define THREAD_SIZE		SZ_16K
+#define THREAD_MASK		(THREAD_SIZE - 1UL)
+#define THREAD_SIZE_ORDER	ilog2(THREAD_SIZE / PAGE_SIZE)
+/*
+ * thread information flags
+ * - these are process state flags that various assembly files may need to
+ *   access
+ * - pending work-to-be-done flags are in LSW
+ * - other flags in MSW
+ */
+#define TIF_SIGPENDING		1	/* signal pending */
+#define TIF_NEED_RESCHED	2	/* rescheduling necessary */
+#define TIF_NOTIFY_RESUME	3	/* callback before returning to user */
+#define TIF_NOTIFY_SIGNAL	4	/* signal notifications exist */
+#define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */
+#define TIF_NOHZ		6	/* in adaptive nohz mode */
+#define TIF_UPROBE		7	/* breakpointed or singlestepping */
+#define TIF_USEDFPU		8	/* FPU was used by this task this quantum (SMP) */
+#define TIF_USEDSIMD		9	/* SIMD has been used this quantum */
+#define TIF_MEMDIE		10	/* is terminating due to OOM killer */
+#define TIF_FIXADE		11	/* Fix address errors in software */
+#define TIF_LOGADE		12	/* Log address errors to syslog */
+#define TIF_32BIT_REGS		13	/* 32-bit general purpose registers */
+#define TIF_32BIT_ADDR		14	/* 32-bit address space */
+#define TIF_LOAD_WATCH		15	/* If set, load watch registers */
+#define TIF_SINGLESTEP		16	/* Single Step */
+#define TIF_LSX_CTX_LIVE	17	/* LSX context must be preserved */
+#define TIF_LASX_CTX_LIVE	18	/* LASX context must be preserved */
+
+#define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
+#define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
+#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
+#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
+#define _TIF_NOHZ		(1<<TIF_NOHZ)
+#define _TIF_UPROBE		(1<<TIF_UPROBE)
+#define _TIF_USEDFPU		(1<<TIF_USEDFPU)
+#define _TIF_USEDSIMD		(1<<TIF_USEDSIMD)
+#define _TIF_FIXADE		(1<<TIF_FIXADE)
+#define _TIF_LOGADE		(1<<TIF_LOGADE)
+#define _TIF_32BIT_REGS		(1<<TIF_32BIT_REGS)
+#define _TIF_32BIT_ADDR		(1<<TIF_32BIT_ADDR)
+#define _TIF_LOAD_WATCH		(1<<TIF_LOAD_WATCH)
+#define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
+#define _TIF_LSX_CTX_LIVE	(1<<TIF_LSX_CTX_LIVE)
+#define _TIF_LASX_CTX_LIVE	(1<<TIF_LASX_CTX_LIVE)
+
+#endif /* __KERNEL__ */
+#endif /* _ASM_THREAD_INFO_H */