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

@@ -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 */

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  */

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 */

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 */