LoongArch: Add Loongson Binary Translation (LBT) extension support

Loongson Binary Translation (LBT) is used to accelerate binary translation,
which contains 4 scratch registers (scr0 to scr3), x86/ARM eflags (eflags)
and x87 fpu stack pointer (ftop).

This patch support kernel to save/restore these registers, handle the LBT
exception and maintain sigcontext.

Signed-off-by: Qi Hu <huqi@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 109 insertions, 0 deletions

diff --git a/arch/loongarch/include/asm/lbt.h b/arch/loongarch/include/asm/lbt.h
new file mode 100644
index 000000000000..e671978bf552
--- /dev/null
+++ b/arch/loongarch/include/asm/lbt.h
@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Author: Qi Hu <huqi@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ * Copyright (C) 2020-2023 Loongson Technology Corporation Limited
+ */
+#ifndef _ASM_LBT_H
+#define _ASM_LBT_H
+
+#include <asm/cpu.h>
+#include <asm/current.h>
+#include <asm/loongarch.h>
+#include <asm/processor.h>
+
+extern void _init_lbt(void);
+extern void _save_lbt(struct loongarch_lbt *);
+extern void _restore_lbt(struct loongarch_lbt *);
+
+static inline int is_lbt_enabled(void)
+{
+	if (!cpu_has_lbt)
+		return 0;
+
+	return (csr_read32(LOONGARCH_CSR_EUEN) & CSR_EUEN_LBTEN) ?
+		1 : 0;
+}
+
+static inline int is_lbt_owner(void)
+{
+	return test_thread_flag(TIF_USEDLBT);
+}
+
+#ifdef CONFIG_CPU_HAS_LBT
+
+static inline void enable_lbt(void)
+{
+	if (cpu_has_lbt)
+		csr_xchg32(CSR_EUEN_LBTEN, CSR_EUEN_LBTEN, LOONGARCH_CSR_EUEN);
+}
+
+static inline void disable_lbt(void)
+{
+	if (cpu_has_lbt)
+		csr_xchg32(0, CSR_EUEN_LBTEN, LOONGARCH_CSR_EUEN);
+}
+
+static inline void __own_lbt(void)
+{
+	enable_lbt();
+	set_thread_flag(TIF_USEDLBT);
+	KSTK_EUEN(current) |= CSR_EUEN_LBTEN;
+}
+
+static inline void own_lbt_inatomic(int restore)
+{
+	if (cpu_has_lbt && !is_lbt_owner()) {
+		__own_lbt();
+		if (restore)
+			_restore_lbt(&current->thread.lbt);
+	}
+}
+
+static inline void own_lbt(int restore)
+{
+	preempt_disable();
+	own_lbt_inatomic(restore);
+	preempt_enable();
+}
+
+static inline void lose_lbt_inatomic(int save, struct task_struct *tsk)
+{
+	if (cpu_has_lbt && is_lbt_owner()) {
+		if (save)
+			_save_lbt(&tsk->thread.lbt);
+
+		disable_lbt();
+		clear_tsk_thread_flag(tsk, TIF_USEDLBT);
+	}
+	KSTK_EUEN(tsk) &= ~(CSR_EUEN_LBTEN);
+}
+
+static inline void lose_lbt(int save)
+{
+	preempt_disable();
+	lose_lbt_inatomic(save, current);
+	preempt_enable();
+}
+
+static inline void init_lbt(void)
+{
+	__own_lbt();
+	_init_lbt();
+}
+#else
+static inline void own_lbt_inatomic(int restore) {}
+static inline void lose_lbt_inatomic(int save, struct task_struct *tsk) {}
+static inline void init_lbt(void) {}
+static inline void lose_lbt(int save) {}
+#endif
+
+static inline int thread_lbt_context_live(void)
+{
+	if (!cpu_has_lbt)
+		return 0;
+
+	return test_thread_flag(TIF_LBT_CTX_LIVE);
+}
+
+#endif /* _ASM_LBT_H */