aarch64: userspace: Introduce arch_is_user_context

The arch_is_user_context() function is relying on the content of the
tpidrro_el0 register to determine whether we are in user context or not.

This register is set to '1' when in EL1 and set back to '0' when user
threads are running in userspace.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

arch/arm/core/aarch64/thread.c

@@ -52,6 +52,8 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 	} else {
 		pInitCtx->elr = (uint64_t)z_thread_entry;
 	}
+
+	pInitCtx->tpidrro_el0 = 0x0;
 #else
 	pInitCtx->elr = (uint64_t)z_thread_entry;
 #endif
@@ -95,6 +97,9 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
 	pInitCtx->spsr = DAIF_FIQ_BIT | SPSR_MODE_EL0T;
 	pInitCtx->elr = (uint64_t)z_thread_entry;
 
+	/* The thread will be in user context */
+	pInitCtx->tpidrro_el0 = 0x1;
+
 	pInitCtx->x0 = (uint64_t)user_entry;
 	pInitCtx->x1 = (uint64_t)p1;
 	pInitCtx->x2 = (uint64_t)p2;

arch/arm/core/aarch64/vector_table.S

@@ -55,6 +55,15 @@ _ASM_FILE_PROLOGUE
 	mrs	\xreg1, elr_el1
 	stp	\xreg0, \xreg1, [sp, ___esf_t_spsr_elr_OFFSET]
 
+#ifdef CONFIG_USERSPACE
+	/* Save the current kernel/user mode in the context */
+	mrs	\xreg0, tpidrro_el0
+	str	\xreg0, [sp, ___esf_t_tpidrro_el0_OFFSET]
+
+	/* Switch TPIDRRO_EL0 to kernel mode */
+	msr	tpidrro_el0, xzr
+#endif
+
 .endm
 
 /*
@@ -201,6 +210,12 @@ SECTION_FUNC(TEXT, z_arm64_exit_exc)
 	msr	spsr_el1, x0
 	msr	elr_el1, x1
 
+#ifdef CONFIG_USERSPACE
+	/* Restore the kernel/user mode flag */
+	ldr	x0, [sp, ___esf_t_tpidrro_el0_OFFSET]
+	msr	tpidrro_el0, x0
+#endif
+
 	ldp	x0, x1, [sp, ___esf_t_x0_x1_OFFSET]
 	ldp	x2, x3, [sp, ___esf_t_x2_x3_OFFSET]
 	ldp	x4, x5, [sp, ___esf_t_x4_x5_OFFSET]

arch/arm/core/offsets/offsets_aarch64.c

@@ -39,6 +39,9 @@ GEN_NAMED_OFFSET_SYM(_callee_saved_t, x29, x29_sp);
 GEN_ABSOLUTE_SYM(___callee_saved_t_SIZEOF, sizeof(struct _callee_saved));
 
 GEN_NAMED_OFFSET_SYM(_esf_t, spsr, spsr_elr);
+#ifdef CONFIG_USERSPACE
+GEN_NAMED_OFFSET_SYM(_esf_t, tpidrro_el0, tpidrro_el0);
+#endif
 GEN_NAMED_OFFSET_SYM(_esf_t, x18, x18_x30);
 GEN_NAMED_OFFSET_SYM(_esf_t, x16, x16_x17);
 GEN_NAMED_OFFSET_SYM(_esf_t, x14, x14_x15);

include/arch/arm/aarch64/exc.h

@@ -47,6 +47,9 @@ struct __esf {
 	uint64_t x30;
 	uint64_t spsr;
 	uint64_t elr;
+#ifdef CONFIG_USERSPACE
+	uint64_t tpidrro_el0;
+#endif
 };
 
 typedef struct __esf z_arch_esf_t;

include/arch/arm/aarch64/syscall.h

@@ -6,9 +6,9 @@
 
 /**
  * @file
- * @brief ARM specific syscall header
+ * @brief ARM64 specific syscall header
  *
- * This header contains the ARM specific syscall interface.  It is
+ * This header contains the ARM64 specific syscall interface.  It is
  * included by the syscall interface architecture-abstraction header
  * (include/arch/aarch64/syscall.h)
  */
@@ -20,4 +20,31 @@
 #define _SVC_CALL_IRQ_OFFLOAD		1
 #define _SVC_CALL_RUNTIME_EXCEPT	2
 
+#ifdef CONFIG_USERSPACE
+#ifndef _ASMLANGUAGE
+
+#include <zephyr/types.h>
+#include <stdbool.h>
+#include <arch/arm/aarch64/cpu.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static inline bool arch_is_user_context(void)
+{
+	uint64_t tpidrro_el0;
+
+	__asm__ volatile("mrs %0, tpidrro_el0" : "=r" (tpidrro_el0));
+
+	return (tpidrro_el0 != 0x0);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _ASMLANGUAGE */
+#endif /* CONFIG_USERSPACE */
+
 #endif /* ZEPHYR_INCLUDE_ARCH_ARM_AARCH64_SYSCALL_H_ */

include/arch/syscall.h

@@ -15,6 +15,8 @@
 #else
 #include <arch/x86/ia32/syscall.h>
 #endif
+#elif defined(CONFIG_ARM64)
+#include <arch/arm/aarch64/syscall.h>
 #elif defined(CONFIG_ARM)
 #include <arch/arm/aarch32/syscall.h>
 #elif defined(CONFIG_ARC)