arch: riscv: core: run zephyr completely in user/supervisor mode

Before that fix, zephyr was able to start only in machine mode. With that fix, zephyr can start (as guest) in user or supervisor mode. Fixes zephyrproject-rtos#68133 Signed-off-by: Sven Ginka <[email protected]>
tswaehn · Aug 8, 2024 · c1e4186 · c1e4186
1 parent ed018f8
commit c1e4186
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Showing 13 changed files with 121 additions and 42 deletions.
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
@@ -206,6 +206,18 @@ config RISCV_GENERIC_TOOLCHAIN
 	  Allow SOCs that have custom extended riscv ISA to still
 	  compile with generic riscv32 toolchain.
 
+config RISCV_KERNEL_IN_USER_MODE
+	bool "Start zephyr in user mode"
+	help
+	  Replaces CSR access from machine mode to user mode.
+	  Allows zephyr to run as guest in user mode only
+
+config RISCV_KERNEL_IN_SUPERVISOR_MODE
+	bool "Start zephyr in supervisor mode"
+	help
+	  Replaces CSR access from machine mode to supervisor mode.
+	  Allows zephyr to run as guest in supervisor mode only
+
 config GEN_ISR_TABLES
 	default y
 

diff --git a/arch/riscv/core/cpu_idle.c b/arch/riscv/core/cpu_idle.c
@@ -11,7 +11,7 @@ void __weak arch_cpu_idle(void)
 {
 	sys_trace_idle();
 	__asm__ volatile("wfi");
-	irq_unlock(MSTATUS_IEN);
+	irq_unlock(XSTATUS_IEN);
 }
 
 void __weak arch_cpu_atomic_idle(unsigned int key)

diff --git a/arch/riscv/core/fatal.c b/arch/riscv/core/fatal.c
@@ -79,8 +79,8 @@ FUNC_NORETURN void z_riscv_fatal_error_csf(unsigned int reason, const struct arc
 #endif /* CONFIG_RISCV_ISA_RV32E */
 		LOG_ERR("     sp: " PR_REG, z_riscv_get_sp_before_exc(esf));
 		LOG_ERR("     ra: " PR_REG, esf->ra);
-		LOG_ERR("   mepc: " PR_REG, esf->mepc);
-		LOG_ERR("mstatus: " PR_REG, esf->mstatus);
+		LOG_ERR("   xepc: " PR_REG, esf->xepc);
+		LOG_ERR("xstatus: " PR_REG, esf->xstatus);
 		LOG_ERR("");
 	}
 

diff --git a/arch/riscv/core/irq_manage.c b/arch/riscv/core/irq_manage.c
@@ -19,15 +19,15 @@ LOG_MODULE_DECLARE(os, CONFIG_KERNEL_LOG_LEVEL);
 
 FUNC_NORETURN void z_irq_spurious(const void *unused)
 {
-	unsigned long mcause;
+	unsigned long xcause;
 
 	ARG_UNUSED(unused);
 
-	mcause = csr_read(mcause);
+	xcause = csr_read(xcause);
 
-	mcause &= CONFIG_RISCV_MCAUSE_EXCEPTION_MASK;
+	xcause &= CONFIG_RISCV_MCAUSE_EXCEPTION_MASK;
 
-	LOG_ERR("Spurious interrupt detected! IRQ: %ld", mcause);
+	LOG_ERR("Spurious interrupt detected! IRQ: %ld", xcause);
 #if defined(CONFIG_RISCV_HAS_PLIC)
 	if (mcause == RISCV_IRQ_MEXT) {
 		unsigned int save_irq = riscv_plic_get_irq();

diff --git a/arch/riscv/core/isr.S b/arch/riscv/core/isr.S
@@ -2,6 +2,7 @@
  * Copyright (c) 2016 Jean-Paul Etienne <[email protected]>
  * Copyright (c) 2018 Foundries.io Ltd
  * Copyright (c) 2020 BayLibre, SAS
+ * Copyright (c) 2024 sensry GmbH
  *
  * SPDX-License-Identifier: Apache-2.0
  */
@@ -189,12 +190,12 @@ SECTION_FUNC(exception.entry, _isr_wrapper)
 	get_current_cpu s0
 
 	/* Save MEPC register */
-	csrr t0, mepc
-	sr t0, __struct_arch_esf_mepc_OFFSET(sp)
+	csrr t0, xepc
+	sr t0, __struct_arch_esf_xepc_OFFSET(sp)
 
 	/* Save MSTATUS register */
-	csrr t2, mstatus
-	sr t2, __struct_arch_esf_mstatus_OFFSET(sp)
+	csrr t2, xstatus
+	sr t2, __struct_arch_esf_xstatus_OFFSET(sp)
 
 #if defined(CONFIG_FPU_SHARING)
 	/* determine if FPU access was disabled */
@@ -319,7 +320,7 @@ no_fp:	/* increment _current->arch.exception_depth */
 	jal ra, __soc_is_irq
 	bnez a0, is_interrupt
 #else
-	csrr t0, mcause
+	csrr t0, xcause
 	srli t0, t0, RISCV_MCAUSE_IRQ_POS
 	bnez t0, is_interrupt
 #endif
@@ -329,7 +330,7 @@ no_fp:	/* increment _current->arch.exception_depth */
 	 * perform a context-switch or an IRQ offload. Otherwise call _Fault
 	 * to report the exception.
 	 */
-	csrr t0, mcause
+	csrr t0, xcause
 	li t2, CONFIG_RISCV_MCAUSE_EXCEPTION_MASK
 	and t0, t0, t2
 
@@ -385,9 +386,9 @@ is_kernel_syscall:
 	 * It's safe to always increment by 4, even with compressed
 	 * instructions, because the ecall instruction is always 4 bytes.
 	 */
-	lr t0, __struct_arch_esf_mepc_OFFSET(sp)
+	lr t0, __struct_arch_esf_xepc_OFFSET(sp)
 	addi t0, t0, 4
-	sr t0, __struct_arch_esf_mepc_OFFSET(sp)
+	sr t0, __struct_arch_esf_xepc_OFFSET(sp)
 
 #ifdef CONFIG_PMP_STACK_GUARD
 	/* Re-activate PMP for m-mode */
@@ -505,9 +506,9 @@ is_user_syscall:
 	 * Same as for is_kernel_syscall: increment saved MEPC by 4 to
 	 * prevent triggering the same ecall again upon exiting the ISR.
 	 */
-	lr t1, __struct_arch_esf_mepc_OFFSET(sp)
+	lr t1, __struct_arch_esf_xepc_OFFSET(sp)
 	addi t1, t1, 4
-	sr t1, __struct_arch_esf_mepc_OFFSET(sp)
+	sr t1, __struct_arch_esf_xepc_OFFSET(sp)
 
 	/* Restore argument registers from user stack */
 	lr a0, __struct_arch_esf_a0_OFFSET(sp)
@@ -565,7 +566,7 @@ is_interrupt:
 	 * If we came from userspace then we need to reconfigure the
 	 * PMP for kernel mode stack guard.
 	 */
-	lr t0, __struct_arch_esf_mstatus_OFFSET(sp)
+	lr t0, __struct_arch_esf_xstatus_OFFSET(sp)
 	li t1, MSTATUS_MPP
 	and t0, t0, t1
 	bnez t0, 1f
@@ -609,7 +610,7 @@ on_irq_stack:
 #endif
 
 	/* Get IRQ causing interrupt */
-	csrr a0, mcause
+	csrr a0, xcause
 	li t0, CONFIG_RISCV_MCAUSE_EXCEPTION_MASK
 	and a0, a0, t0
 
@@ -714,10 +715,10 @@ fp_trap_exit:
 #endif
 
 	/* Restore MEPC and MSTATUS registers */
-	lr t0, __struct_arch_esf_mepc_OFFSET(sp)
-	lr t2, __struct_arch_esf_mstatus_OFFSET(sp)
-	csrw mepc, t0
-	csrw mstatus, t2
+	lr t0, __struct_arch_esf_xepc_OFFSET(sp)
+	lr t2, __struct_arch_esf_xstatus_OFFSET(sp)
+	csrw xepc, t0
+	csrw xstatus, t2
 
 #ifdef CONFIG_USERSPACE
 	/*
@@ -775,4 +776,4 @@ fp_trap_exit:
 
 #endif /* CONFIG_RISCV_SOC_HAS_ISR_STACKING */
 
-	mret
+	xret
diff --git a/arch/riscv/core/offsets/offsets.c b/arch/riscv/core/offsets/offsets.c
@@ -13,9 +13,9 @@
  * structures.
  */
 
-#include <zephyr/arch/exception.h>
 #include <zephyr/kernel.h>
 #include <kernel_arch_data.h>
+#include <zephyr/arch/exception.h>
 #include <gen_offset.h>
 
 #ifdef CONFIG_RISCV_SOC_CONTEXT_SAVE
@@ -109,8 +109,8 @@ GEN_OFFSET_STRUCT(arch_esf, a6);
 GEN_OFFSET_STRUCT(arch_esf, a7);
 #endif /* !CONFIG_RISCV_ISA_RV32E */
 
-GEN_OFFSET_STRUCT(arch_esf, mepc);
-GEN_OFFSET_STRUCT(arch_esf, mstatus);
+GEN_OFFSET_STRUCT(arch_esf, xepc);
+GEN_OFFSET_STRUCT(arch_esf, xstatus);
 
 GEN_OFFSET_STRUCT(arch_esf, s0);
 

diff --git a/arch/riscv/core/reset.S b/arch/riscv/core/reset.S
@@ -38,7 +38,7 @@ SECTION_FUNC(reset, __reset)
  * the C domain
  */
 SECTION_FUNC(TEXT, __initialize)
-	csrr a0, mhartid
+	csrr a0, xhartid
 	li t0, CONFIG_RV_BOOT_HART
 	beq a0, t0, boot_first_core
 	j boot_secondary_core

diff --git a/arch/riscv/core/stacktrace.c b/arch/riscv/core/stacktrace.c
@@ -165,7 +165,7 @@ static void walk_stackframe(stack_trace_callback_fn cb, void *cookie, const stru
 	if (esf != NULL) {
 		/* Unwind the provided exception stack frame */
 		sp = z_riscv_get_sp_before_exc(esf);
-		ra = esf->mepc;
+		ra = esf->xepc;
 	} else if ((csf == NULL) || (csf == &_current->callee_saved)) {
 		/* Unwind current thread (default case when nothing is provided ) */
 		sp = current_stack_pointer;

diff --git a/arch/riscv/core/thread.c b/arch/riscv/core/thread.c
@@ -63,7 +63,7 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 	 *    counter will be restored following the MEPC value set within the
 	 *    thread stack.
 	 */
-	stack_init->mstatus = MSTATUS_DEF_RESTORE;
+	stack_init->xstatus = XSTATUS_DEF_RESTORE;
 
 #if defined(CONFIG_FPU_SHARING)
 	/* thread birth happens through the exception return path */
@@ -83,11 +83,11 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 	if (IS_ENABLED(CONFIG_USERSPACE)
 	    && (thread->base.user_options & K_USER)) {
 		/* User thread */
-		stack_init->mepc = (unsigned long)k_thread_user_mode_enter;
+		stack_init->xepc = (unsigned long)k_thread_user_mode_enter;
 
 	} else {
 		/* Supervisor thread */
-		stack_init->mepc = (unsigned long)z_thread_entry;
+		stack_init->xepc = (unsigned long)z_thread_entry;
 
 #if defined(CONFIG_PMP_STACK_GUARD)
 		/* Enable PMP in mstatus.MPRV mode for RISC-V machine mode

diff --git a/include/zephyr/arch/riscv/arch.h b/include/zephyr/arch/riscv/arch.h
@@ -166,6 +166,12 @@
 #define MSTATUS_FS_CLEAN (2UL << 13)
 #define MSTATUS_FS_DIRTY (3UL << 13)
 
+#define SSTATUS_IEN      (1UL << 1)
+#define SSTATUS_UPIE_IEN (1UL << 5)
+
+#define USTATUS_IEN      (1UL << 0)
+#define USTATUS_UPIE_IEN (1UL << 4)
+
 /* This comes from openisa_rv32m1, but doesn't seem to hurt on other
  * platforms:
  * - Preserve machine privileges in MPP. If you see any documentation
@@ -175,6 +181,8 @@
  *   by setting MPIE now, so it will be copied into IE on mret.
  */
 #define MSTATUS_DEF_RESTORE (MSTATUS_MPP_M | MSTATUS_MPIE_EN)
+#define SSTATUS_DEF_RESTORE (SSTATUS_UPIE_IEN | SSTATUS_IEN)
+#define USTATUS_DEF_RESTORE (USTATUS_UPIE_IEN | USTATUS_IEN)
 
 #ifndef _ASMLANGUAGE
 #include <zephyr/sys/util.h>
@@ -238,9 +246,9 @@ static ALWAYS_INLINE unsigned int arch_irq_lock(void)
 #else
 	unsigned int key;
 
-	__asm__ volatile ("csrrc %0, mstatus, %1"
+	__asm__ volatile ("csrrc %0, %1, %2"
 			  : "=r" (key)
-			  : "rK" (MSTATUS_IEN)
+			  : "i" (XSTATUS), "rK" (XSTATUS_IEN)
 			  : "memory");
 
 	return key;
@@ -254,21 +262,23 @@ static ALWAYS_INLINE unsigned int arch_irq_lock(void)
 static ALWAYS_INLINE void arch_irq_unlock(unsigned int key)
 {
 #ifdef CONFIG_RISCV_SOC_HAS_CUSTOM_IRQ_LOCK_OPS
+	extern void z_soc_irq_unlock(unsigned int key);
 	z_soc_irq_unlock(key);
 #else
-	__asm__ volatile ("csrs mstatus, %0"
+	__asm__ volatile ("csrs %0, %1"
 			  :
-			  : "r" (key & MSTATUS_IEN)
+			  : "i" (XSTATUS), "r" (key & XSTATUS_IEN)
 			  : "memory");
 #endif
 }
 
 static ALWAYS_INLINE bool arch_irq_unlocked(unsigned int key)
 {
 #ifdef CONFIG_RISCV_SOC_HAS_CUSTOM_IRQ_LOCK_OPS
+	extern bool z_soc_irq_unlocked(unsigned int key);
 	return z_soc_irq_unlocked(key);
 #else
-	return (key & MSTATUS_IEN) != 0;
+	return (key & XSTATUS_IEN) != 0;
 #endif
 }
 

diff --git a/include/zephyr/arch/riscv/csr.h b/include/zephyr/arch/riscv/csr.h
@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2020 Michael Schaffner
  * Copyright (c) 2020 BayLibre, SAS
+ * Copyright (c) 2024 sensry GmbH
  *
  * SPDX-License-Identifier: SHL-0.51
  * SPDX-License-Identifier: Apache-2.0
@@ -233,4 +234,59 @@
 				: "memory");			\
 })
 
+/* uhartid -- user hardware thread id, seems to be not yet defined in toolchain */
+#ifdef CONFIG_RISCV_KERNEL_IN_USER_MODE
+	/* zephyr runs in user mode */
+
+	/* inline assembly defines */
+	#define XSTATUS_IEN			USTATUS_IEN
+	#define XSTATUS_DEF_RESTORE		USTATUS_DEF_RESTORE
+	#define XSTATUS				0x000
+
+	/* register definition for assembly */
+	#define	uhartid				0x014
+
+	#define xhartid				uhartid
+	#define xscratch			uscratch
+	#define xstatus				ustatus
+	#define xepc				uepc
+	#define xcause				ucause
+	#define xret				uret
+
+#elif CONFIG_RISCV_KERNEL_IN_SUPERVISOR_MODE
+	/* zephyr runs in supervisor mode */
+
+	/* inline assembly defines */
+	#define XSTATUS_IEN			SSTATUS_IEN
+	#define XSTATUS_DEF_RESTORE		SSTATUS_DEF_RESTORE
+	#define XSTATUS				0x000
+
+	/* register definition for assembly */
+	#define	shartid				0x7D2
+
+	#define xhartid				shartid
+	#define xscratch			sscratch
+	#define xstatus				sstatus
+	#define xepc				0x141
+	#define xcause				scause
+	#define xret				sret
+
+#else
+	/* default: zephyr runs in machine mode */
+
+	/* inline assembly defines */
+	#define XSTATUS_IEN			MSTATUS_IEN
+	#define XSTATUS_DEF_RESTORE		MSTATUS_DEF_RESTORE
+	#define XSTATUS				0x300
+
+	/* register definition for assembly */
+	#define xhartid				mhartid
+	#define xscratch			mscratch
+	#define xstatus				mstatus
+	#define xepc				mepc
+	#define xcause				mcause
+	#define xret				mret
+
+#endif
+
 #endif /* CSR_H_ */
diff --git a/include/zephyr/arch/riscv/exception.h b/include/zephyr/arch/riscv/exception.h
@@ -72,8 +72,8 @@ struct arch_esf {
 	unsigned long a7;		/* function argument */
 #endif /* !CONFIG_RISCV_ISA_RV32E */
 
-	unsigned long mepc;		/* machine exception program counter */
-	unsigned long mstatus;	/* machine status register */
+	unsigned long xepc;		/* machine exception program counter */
+	unsigned long xstatus;		/* machine status register */
 
 	unsigned long s0;		/* callee-saved s0 */
 

diff --git a/soc/nordic/common/vpr/soc_isr_stacking.h b/soc/nordic/common/vpr/soc_isr_stacking.h
@@ -91,16 +91,16 @@
 
 #define STORE_SP_ALIGN_BIT_FROM_MEPC				\
 	addi t1, sp, __struct_arch_esf_soc_context_OFFSET;	\
-	lr t0, __struct_arch_esf_mepc_OFFSET(sp);		\
+	lr t0, __struct_arch_esf_xepc_OFFSET(sp);		\
 	andi t0, t0, MEPC_SP_ALIGN_BIT_MASK;			\
 	sr t0, __soc_esf_t_sp_align_OFFSET(t1)
 
 #define RESTORE_SP_ALIGN_BIT_TO_MEPC				\
 	addi t1, sp, __struct_arch_esf_soc_context_OFFSET;	\
 	lr t0, __soc_esf_t_sp_align_OFFSET(t1);			\
-	lr t1, __struct_arch_esf_mepc_OFFSET(sp);		\
+	lr t1, __struct_arch_esf_xepc_OFFSET(sp);		\
 	or t2, t1, t0;						\
-	sr t2, __struct_arch_esf_mepc_OFFSET(sp)
+	sr t2, __struct_arch_esf_xepc_OFFSET(sp)
 
 #define SOC_ISR_SW_STACKING			\
 	csrw mscratch, t0;			\