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>

arch/loongarch/include/asm/fpu.h

+/* 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 */

arch/loongarch/include/asm/idle.h

+/* 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  */

arch/loongarch/include/asm/mmu.h

+/* 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 */

arch/loongarch/include/asm/mmu_context.h

+/* 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 */

arch/loongarch/include/asm/processor.h

+/* 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 */

arch/loongarch/include/asm/ptrace.h

+/* 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 */

arch/loongarch/include/asm/switch_to.h

+/* 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 */

arch/loongarch/include/asm/thread_info.h

+/* 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 */

arch/loongarch/include/uapi/asm/ptrace.h

+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_PTRACE_H
+#define _UAPI_ASM_PTRACE_H
+
+#include <linux/types.h>
+
+#ifndef __KERNEL__
+#include <stdint.h>
+#endif
+
+/*
+ * For PTRACE_{POKE,PEEK}USR. 0 - 31 are GPRs,
+ * 32 is syscall's original ARG0, 33 is PC, 34 is BADVADDR.
+ */
+#define GPR_BASE	0
+#define GPR_NUM		32
+#define GPR_END		(GPR_BASE + GPR_NUM - 1)
+#define ARG0		(GPR_END + 1)
+#define PC		(GPR_END + 2)
+#define BADVADDR	(GPR_END + 3)
+
+#define NUM_FPU_REGS	32
+
+struct user_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_badv;
+	unsigned long reserved[10];
+} __attribute__((aligned(8)));
+
+struct user_fp_state {
+	uint64_t    fpr[32];
+	uint64_t    fcc;
+	uint32_t    fcsr;
+};
+
+#define PTRACE_SYSEMU			0x1f
+#define PTRACE_SYSEMU_SINGLESTEP	0x20
+
+#endif /* _UAPI_ASM_PTRACE_H */

arch/loongarch/kernel/fpu.S

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Author: Lu Zeng <zenglu@loongson.cn>
+ *         Pei Huang <huangpei@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#include <asm/asm.h>
+#include <asm/asmmacro.h>
+#include <asm/asm-offsets.h>
+#include <asm/errno.h>
+#include <asm/export.h>
+#include <asm/fpregdef.h>
+#include <asm/loongarch.h>
+#include <asm/regdef.h>
+
+#define FPU_REG_WIDTH		8
+#define LSX_REG_WIDTH		16
+#define LASX_REG_WIDTH		32
+
+	.macro	EX insn, reg, src, offs
+.ex\@:	\insn	\reg, \src, \offs
+	.section __ex_table,"a"
+	PTR	.ex\@, fault
+	.previous
+	.endm
+
+	.macro sc_save_fp base
+	EX	fst.d $f0,  \base, (0 * FPU_REG_WIDTH)
+	EX	fst.d $f1,  \base, (1 * FPU_REG_WIDTH)
+	EX	fst.d $f2,  \base, (2 * FPU_REG_WIDTH)
+	EX	fst.d $f3,  \base, (3 * FPU_REG_WIDTH)
+	EX	fst.d $f4,  \base, (4 * FPU_REG_WIDTH)
+	EX	fst.d $f5,  \base, (5 * FPU_REG_WIDTH)
+	EX	fst.d $f6,  \base, (6 * FPU_REG_WIDTH)
+	EX	fst.d $f7,  \base, (7 * FPU_REG_WIDTH)
+	EX	fst.d $f8,  \base, (8 * FPU_REG_WIDTH)
+	EX	fst.d $f9,  \base, (9 * FPU_REG_WIDTH)
+	EX	fst.d $f10, \base, (10 * FPU_REG_WIDTH)
+	EX	fst.d $f11, \base, (11 * FPU_REG_WIDTH)
+	EX	fst.d $f12, \base, (12 * FPU_REG_WIDTH)
+	EX	fst.d $f13, \base, (13 * FPU_REG_WIDTH)
+	EX	fst.d $f14, \base, (14 * FPU_REG_WIDTH)
+	EX	fst.d $f15, \base, (15 * FPU_REG_WIDTH)
+	EX	fst.d $f16, \base, (16 * FPU_REG_WIDTH)
+	EX	fst.d $f17, \base, (17 * FPU_REG_WIDTH)
+	EX	fst.d $f18, \base, (18 * FPU_REG_WIDTH)
+	EX	fst.d $f19, \base, (19 * FPU_REG_WIDTH)
+	EX	fst.d $f20, \base, (20 * FPU_REG_WIDTH)
+	EX	fst.d $f21, \base, (21 * FPU_REG_WIDTH)
+	EX	fst.d $f22, \base, (22 * FPU_REG_WIDTH)
+	EX	fst.d $f23, \base, (23 * FPU_REG_WIDTH)
+	EX	fst.d $f24, \base, (24 * FPU_REG_WIDTH)
+	EX	fst.d $f25, \base, (25 * FPU_REG_WIDTH)
+	EX	fst.d $f26, \base, (26 * FPU_REG_WIDTH)
+	EX	fst.d $f27, \base, (27 * FPU_REG_WIDTH)
+	EX	fst.d $f28, \base, (28 * FPU_REG_WIDTH)
+	EX	fst.d $f29, \base, (29 * FPU_REG_WIDTH)
+	EX	fst.d $f30, \base, (30 * FPU_REG_WIDTH)
+	EX	fst.d $f31, \base, (31 * FPU_REG_WIDTH)
+	.endm
+
+	.macro sc_restore_fp base
+	EX	fld.d $f0,  \base, (0 * FPU_REG_WIDTH)
+	EX	fld.d $f1,  \base, (1 * FPU_REG_WIDTH)
+	EX	fld.d $f2,  \base, (2 * FPU_REG_WIDTH)
+	EX	fld.d $f3,  \base, (3 * FPU_REG_WIDTH)
+	EX	fld.d $f4,  \base, (4 * FPU_REG_WIDTH)
+	EX	fld.d $f5,  \base, (5 * FPU_REG_WIDTH)
+	EX	fld.d $f6,  \base, (6 * FPU_REG_WIDTH)
+	EX	fld.d $f7,  \base, (7 * FPU_REG_WIDTH)
+	EX	fld.d $f8,  \base, (8 * FPU_REG_WIDTH)
+	EX	fld.d $f9,  \base, (9 * FPU_REG_WIDTH)
+	EX	fld.d $f10, \base, (10 * FPU_REG_WIDTH)
+	EX	fld.d $f11, \base, (11 * FPU_REG_WIDTH)
+	EX	fld.d $f12, \base, (12 * FPU_REG_WIDTH)
+	EX	fld.d $f13, \base, (13 * FPU_REG_WIDTH)
+	EX	fld.d $f14, \base, (14 * FPU_REG_WIDTH)
+	EX	fld.d $f15, \base, (15 * FPU_REG_WIDTH)
+	EX	fld.d $f16, \base, (16 * FPU_REG_WIDTH)
+	EX	fld.d $f17, \base, (17 * FPU_REG_WIDTH)
+	EX	fld.d $f18, \base, (18 * FPU_REG_WIDTH)
+	EX	fld.d $f19, \base, (19 * FPU_REG_WIDTH)
+	EX	fld.d $f20, \base, (20 * FPU_REG_WIDTH)
+	EX	fld.d $f21, \base, (21 * FPU_REG_WIDTH)
+	EX	fld.d $f22, \base, (22 * FPU_REG_WIDTH)
+	EX	fld.d $f23, \base, (23 * FPU_REG_WIDTH)
+	EX	fld.d $f24, \base, (24 * FPU_REG_WIDTH)
+	EX	fld.d $f25, \base, (25 * FPU_REG_WIDTH)
+	EX	fld.d $f26, \base, (26 * FPU_REG_WIDTH)
+	EX	fld.d $f27, \base, (27 * FPU_REG_WIDTH)
+	EX	fld.d $f28, \base, (28 * FPU_REG_WIDTH)
+	EX	fld.d $f29, \base, (29 * FPU_REG_WIDTH)
+	EX	fld.d $f30, \base, (30 * FPU_REG_WIDTH)
+	EX	fld.d $f31, \base, (31 * FPU_REG_WIDTH)
+	.endm
+
+	.macro sc_save_fcc base, tmp0, tmp1
+	movcf2gr	\tmp0, $fcc0
+	move	\tmp1, \tmp0
+	movcf2gr	\tmp0, $fcc1
+	bstrins.d	\tmp1, \tmp0, 15, 8
+	movcf2gr	\tmp0, $fcc2
+	bstrins.d	\tmp1, \tmp0, 23, 16
+	movcf2gr	\tmp0, $fcc3
+	bstrins.d	\tmp1, \tmp0, 31, 24
+	movcf2gr	\tmp0, $fcc4
+	bstrins.d	\tmp1, \tmp0, 39, 32
+	movcf2gr	\tmp0, $fcc5
+	bstrins.d	\tmp1, \tmp0, 47, 40
+	movcf2gr	\tmp0, $fcc6
+	bstrins.d	\tmp1, \tmp0, 55, 48
+	movcf2gr	\tmp0, $fcc7
+	bstrins.d	\tmp1, \tmp0, 63, 56
+	EX	st.d \tmp1, \base, 0
+	.endm
+
+	.macro sc_restore_fcc base, tmp0, tmp1
+	EX	ld.d \tmp0, \base, 0
+	bstrpick.d	\tmp1, \tmp0, 7, 0
+	movgr2cf	$fcc0, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 15, 8
+	movgr2cf	$fcc1, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 23, 16
+	movgr2cf	$fcc2, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 31, 24
+	movgr2cf	$fcc3, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 39, 32
+	movgr2cf	$fcc4, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 47, 40
+	movgr2cf	$fcc5, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 55, 48
+	movgr2cf	$fcc6, \tmp1
+	bstrpick.d	\tmp1, \tmp0, 63, 56
+	movgr2cf	$fcc7, \tmp1
+	.endm
+
+	.macro sc_save_fcsr base, tmp0
+	movfcsr2gr	\tmp0, fcsr0
+	EX	st.w \tmp0, \base, 0
+	.endm
+
+	.macro sc_restore_fcsr base, tmp0
+	EX	ld.w \tmp0, \base, 0
+	movgr2fcsr	fcsr0, \tmp0
+	.endm
+
+	.macro sc_save_vcsr base, tmp0
+	movfcsr2gr	\tmp0, vcsr16
+	EX	st.w \tmp0, \base, 0
+	.endm
+
+	.macro sc_restore_vcsr base, tmp0
+	EX	ld.w \tmp0, \base, 0
+	movgr2fcsr	vcsr16, \tmp0
+	.endm
+
+/*
+ * Save a thread's fp context.
+ */
+SYM_FUNC_START(_save_fp)
+	fpu_save_csr	a0 t1
+	fpu_save_double a0 t1			# clobbers t1
+	fpu_save_cc	a0 t1 t2		# clobbers t1, t2
+	jirl zero, ra, 0
+SYM_FUNC_END(_save_fp)
+EXPORT_SYMBOL(_save_fp)
+
+/*
+ * Restore a thread's fp context.
+ */
+SYM_FUNC_START(_restore_fp)
+	fpu_restore_double a0 t1		# clobbers t1
+	fpu_restore_csr	a0 t1
+	fpu_restore_cc	a0 t1 t2		# clobbers t1, t2
+	jirl zero, ra, 0
+SYM_FUNC_END(_restore_fp)
+
+/*
+ * Load the FPU with signalling NANS.  This bit pattern we're using has
+ * the property that no matter whether considered as single or as double
+ * precision represents signaling NANS.
+ *
+ * The value to initialize fcsr0 to comes in $a0.
+ */
+
+SYM_FUNC_START(_init_fpu)
+	li.w	t1, CSR_EUEN_FPEN
+	csrxchg	t1, t1, LOONGARCH_CSR_EUEN
+
+	movgr2fcsr	fcsr0, a0
+
+	li.w	t1, -1				# SNaN
+
+	movgr2fr.d	$f0, t1
+	movgr2fr.d	$f1, t1
+	movgr2fr.d	$f2, t1
+	movgr2fr.d	$f3, t1
+	movgr2fr.d	$f4, t1
+	movgr2fr.d	$f5, t1
+	movgr2fr.d	$f6, t1
+	movgr2fr.d	$f7, t1
+	movgr2fr.d	$f8, t1
+	movgr2fr.d	$f9, t1
+	movgr2fr.d	$f10, t1
+	movgr2fr.d	$f11, t1
+	movgr2fr.d	$f12, t1
+	movgr2fr.d	$f13, t1
+	movgr2fr.d	$f14, t1
+	movgr2fr.d	$f15, t1
+	movgr2fr.d	$f16, t1
+	movgr2fr.d	$f17, t1
+	movgr2fr.d	$f18, t1
+	movgr2fr.d	$f19, t1
+	movgr2fr.d	$f20, t1
+	movgr2fr.d	$f21, t1
+	movgr2fr.d	$f22, t1
+	movgr2fr.d	$f23, t1
+	movgr2fr.d	$f24, t1
+	movgr2fr.d	$f25, t1
+	movgr2fr.d	$f26, t1
+	movgr2fr.d	$f27, t1
+	movgr2fr.d	$f28, t1
+	movgr2fr.d	$f29, t1
+	movgr2fr.d	$f30, t1
+	movgr2fr.d	$f31, t1
+
+	jirl zero, ra, 0
+SYM_FUNC_END(_init_fpu)
+
+/*
+ * a0: fpregs
+ * a1: fcc
+ * a2: fcsr
+ */
+SYM_FUNC_START(_save_fp_context)
+	sc_save_fcc a1 t1 t2
+	sc_save_fcsr a2 t1
+	sc_save_fp a0
+	li.w	a0, 0					# success
+	jirl zero, ra, 0
+SYM_FUNC_END(_save_fp_context)
+
+/*
+ * a0: fpregs
+ * a1: fcc
+ * a2: fcsr
+ */
+SYM_FUNC_START(_restore_fp_context)
+	sc_restore_fp a0
+	sc_restore_fcc a1 t1 t2
+	sc_restore_fcsr a2 t1
+	li.w	a0, 0					# success
+	jirl zero, ra, 0
+SYM_FUNC_END(_restore_fp_context)
+
+SYM_FUNC_START(fault)
+	li.w	a0, -EFAULT				# failure
+	jirl zero, ra, 0
+SYM_FUNC_END(fault)

arch/loongarch/kernel/idle.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * LoongArch idle loop support.
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#include <linux/cpu.h>
+#include <linux/irqflags.h>
+#include <asm/cpu.h>
+#include <asm/idle.h>
+
+void __cpuidle arch_cpu_idle(void)
+{
+	raw_local_irq_enable();
+	__arch_cpu_idle(); /* idle instruction needs irq enabled */
+}

arch/loongarch/kernel/process.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Author: Huacai Chen <chenhuacai@loongson.cn>
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 1994 - 1999, 2000 by Ralf Baechle and others.
+ * Copyright (C) 2005, 2006 by Ralf Baechle (ralf@linux-mips.org)
+ * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
+ * Copyright (C) 2004 Thiemo Seufer
+ * Copyright (C) 2013  Imagination Technologies Ltd.
+ */
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/mm.h>
+#include <linux/stddef.h>
+#include <linux/unistd.h>
+#include <linux/export.h>
+#include <linux/ptrace.h>
+#include <linux/mman.h>
+#include <linux/personality.h>
+#include <linux/sys.h>
+#include <linux/completion.h>
+#include <linux/kallsyms.h>
+#include <linux/random.h>
+#include <linux/prctl.h>
+#include <linux/nmi.h>
+
+#include <asm/asm.h>
+#include <asm/bootinfo.h>
+#include <asm/cpu.h>
+#include <asm/elf.h>
+#include <asm/fpu.h>
+#include <asm/io.h>
+#include <asm/irq.h>
+#include <asm/irq_regs.h>
+#include <asm/loongarch.h>
+#include <asm/pgtable.h>
+#include <asm/processor.h>
+#include <asm/reg.h>
+#include <asm/vdso.h>
+
+/*
+ * Idle related variables and functions
+ */
+
+unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
+EXPORT_SYMBOL(boot_option_idle_override);
+
+asmlinkage void ret_from_fork(void);
+asmlinkage void ret_from_kernel_thread(void);
+
+void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
+{
+	unsigned long crmd;
+	unsigned long prmd;
+	unsigned long euen;
+
+	/* New thread loses kernel privileges. */
+	crmd = regs->csr_crmd & ~(PLV_MASK);
+	crmd |= PLV_USER;
+	regs->csr_crmd = crmd;
+
+	prmd = regs->csr_prmd & ~(PLV_MASK);
+	prmd |= PLV_USER;
+	regs->csr_prmd = prmd;
+
+	euen = regs->csr_euen & ~(CSR_EUEN_FPEN);
+	regs->csr_euen = euen;
+	lose_fpu(0);
+
+	clear_thread_flag(TIF_LSX_CTX_LIVE);
+	clear_thread_flag(TIF_LASX_CTX_LIVE);
+	clear_used_math();
+	regs->csr_era = pc;
+	regs->regs[3] = sp;
+}
+
+void exit_thread(struct task_struct *tsk)
+{
+}
+
+int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
+{
+	/*
+	 * Save any process state which is live in hardware registers to the
+	 * parent context prior to duplication. This prevents the new child
+	 * state becoming stale if the parent is preempted before copy_thread()
+	 * gets a chance to save the parent's live hardware registers to the
+	 * child context.
+	 */
+	preempt_disable();
+
+	if (is_fpu_owner())
+		save_fp(current);
+
+	preempt_enable();
+
+	if (used_math())
+		memcpy(dst, src, sizeof(struct task_struct));
+	else
+		memcpy(dst, src, offsetof(struct task_struct, thread.fpu.fpr));
+
+	return 0;
+}
+
+/*
+ * Copy architecture-specific thread state
+ */
+int copy_thread(unsigned long clone_flags, unsigned long usp,
+	unsigned long kthread_arg, struct task_struct *p, unsigned long tls)
+{
+	unsigned long childksp;
+	struct pt_regs *childregs, *regs = current_pt_regs();
+
+	childksp = (unsigned long)task_stack_page(p) + THREAD_SIZE - 32;
+
+	/* set up new TSS. */
+	childregs = (struct pt_regs *) childksp - 1;
+	/*  Put the stack after the struct pt_regs.  */
+	childksp = (unsigned long) childregs;
+	p->thread.csr_euen = 0;
+	p->thread.csr_crmd = csr_read32(LOONGARCH_CSR_CRMD);
+	p->thread.csr_prmd = csr_read32(LOONGARCH_CSR_PRMD);
+	p->thread.csr_ecfg = csr_read32(LOONGARCH_CSR_ECFG);
+	if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
+		/* kernel thread */
+		p->thread.reg23 = usp; /* fn */
+		p->thread.reg24 = kthread_arg;
+		p->thread.reg03 = childksp;
+		p->thread.reg01 = (unsigned long) ret_from_kernel_thread;
+		memset(childregs, 0, sizeof(struct pt_regs));
+		childregs->csr_euen = p->thread.csr_euen;
+		childregs->csr_crmd = p->thread.csr_crmd;
+		childregs->csr_prmd = p->thread.csr_prmd;
+		childregs->csr_ecfg = p->thread.csr_ecfg;
+		return 0;
+	}
+
+	/* user thread */
+	*childregs = *regs;
+	childregs->regs[4] = 0; /* Child gets zero as return value */
+	if (usp)
+		childregs->regs[3] = usp;
+
+	p->thread.reg03 = (unsigned long) childregs;
+	p->thread.reg01 = (unsigned long) ret_from_fork;
+
+	/*
+	 * New tasks lose permission to use the fpu. This accelerates context
+	 * switching for most programs since they don't use the fpu.
+	 */
+	childregs->csr_euen = 0;
+
+	clear_tsk_thread_flag(p, TIF_USEDFPU);
+	clear_tsk_thread_flag(p, TIF_USEDSIMD);
+	clear_tsk_thread_flag(p, TIF_LSX_CTX_LIVE);
+	clear_tsk_thread_flag(p, TIF_LASX_CTX_LIVE);
+
+	if (clone_flags & CLONE_SETTLS)
+		childregs->regs[2] = tls;
+
+	return 0;
+}
+
+unsigned long __get_wchan(struct task_struct *task)
+{
+	return 0;
+}
+
+unsigned long stack_top(void)
+{
+	unsigned long top = TASK_SIZE & PAGE_MASK;
+
+	/* Space for the VDSO & data page */
+	top -= PAGE_ALIGN(current->thread.vdso->size);
+	top -= PAGE_SIZE;
+
+	/* Space to randomize the VDSO base */
+	if (current->flags & PF_RANDOMIZE)
+		top -= VDSO_RANDOMIZE_SIZE;
+
+	return top;
+}
+
+/*
+ * Don't forget that the stack pointer must be aligned on a 8 bytes
+ * boundary for 32-bits ABI and 16 bytes for 64-bits ABI.
+ */
+unsigned long arch_align_stack(unsigned long sp)
+{
+	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
+		sp -= get_random_int() & ~PAGE_MASK;
+
+	return sp & STACK_ALIGN;
+}
+
+static DEFINE_PER_CPU(call_single_data_t, backtrace_csd);
+static struct cpumask backtrace_csd_busy;
+
+static void handle_backtrace(void *info)
+{
+	nmi_cpu_backtrace(get_irq_regs());
+	cpumask_clear_cpu(smp_processor_id(), &backtrace_csd_busy);
+}
+
+static void raise_backtrace(cpumask_t *mask)
+{
+	call_single_data_t *csd;
+	int cpu;
+
+	for_each_cpu(cpu, mask) {
+		/*
+		 * If we previously sent an IPI to the target CPU & it hasn't
+		 * cleared its bit in the busy cpumask then it didn't handle
+		 * our previous IPI & it's not safe for us to reuse the
+		 * call_single_data_t.
+		 */
+		if (cpumask_test_and_set_cpu(cpu, &backtrace_csd_busy)) {
+			pr_warn("Unable to send backtrace IPI to CPU%u - perhaps it hung?\n",
+				cpu);
+			continue;
+		}
+
+		csd = &per_cpu(backtrace_csd, cpu);
+		csd->func = handle_backtrace;
+		smp_call_function_single_async(cpu, csd);
+	}
+}
+
+void arch_trigger_cpumask_backtrace(const cpumask_t *mask, bool exclude_self)
+{
+	nmi_trigger_cpumask_backtrace(mask, exclude_self, raise_backtrace);
+}
+
+#ifdef CONFIG_64BIT
+void loongarch_dump_regs64(u64 *uregs, const struct pt_regs *regs)
+{
+	unsigned int i;
+
+	for (i = LOONGARCH_EF_R1; i <= LOONGARCH_EF_R31; i++) {
+		uregs[i] = regs->regs[i - LOONGARCH_EF_R0];
+	}
+
+	uregs[LOONGARCH_EF_ORIG_A0] = regs->orig_a0;
+	uregs[LOONGARCH_EF_CSR_ERA] = regs->csr_era;
+	uregs[LOONGARCH_EF_CSR_BADV] = regs->csr_badvaddr;
+	uregs[LOONGARCH_EF_CSR_CRMD] = regs->csr_crmd;
+	uregs[LOONGARCH_EF_CSR_PRMD] = regs->csr_prmd;
+	uregs[LOONGARCH_EF_CSR_EUEN] = regs->csr_euen;
+	uregs[LOONGARCH_EF_CSR_ECFG] = regs->csr_ecfg;
+	uregs[LOONGARCH_EF_CSR_ESTAT] = regs->csr_estat;
+}
+#endif /* CONFIG_64BIT */

arch/loongarch/kernel/switch.S

+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#include <asm/asm.h>
+#include <asm/asmmacro.h>
+#include <asm/asm-offsets.h>
+#include <asm/loongarch.h>
+#include <asm/regdef.h>
+#include <asm/stackframe.h>
+#include <asm/thread_info.h>
+
+/*
+ * task_struct *__switch_to(task_struct *prev, task_struct *next,
+ *			    struct thread_info *next_ti)
+ */
+	.align	5
+SYM_FUNC_START(__switch_to)
+	csrrd	t1, LOONGARCH_CSR_PRMD
+	stptr.d	t1, a0, THREAD_CSRPRMD
+
+	cpu_save_nonscratch a0
+	stptr.d	ra, a0, THREAD_REG01
+	move	tp, a2
+	cpu_restore_nonscratch a1
+
+	li.w	t0, _THREAD_SIZE - 32
+	PTR_ADD	t0, t0, tp
+	set_saved_sp	t0, t1, t2
+
+	ldptr.d	t1, a1, THREAD_CSRPRMD
+	csrwr	t1, LOONGARCH_CSR_PRMD
+
+	jr	ra
+SYM_FUNC_END(__switch_to)