1/* SPDX-License-Identifier: GPL-2.0-only */
2/*
3 * Copyright (C) 2012 Regents of the University of California
4 * Copyright (C) 2017 SiFive
5 */
6
7#include <linux/init.h>
8#include <linux/linkage.h>
9
10#include <asm/asm.h>
11#include <asm/csr.h>
12#include <asm/scs.h>
13#include <asm/unistd.h>
14#include <asm/page.h>
15#include <asm/thread_info.h>
16#include <asm/asm-offsets.h>
17#include <asm/errata_list.h>
18#include <linux/sizes.h>
19
20 .section .irqentry.text, "ax"
21
22SYM_CODE_START(handle_exception)
23 /*
24 * If coming from userspace, preserve the user thread pointer and load
25 * the kernel thread pointer. If we came from the kernel, the scratch
26 * register will contain 0, and we should continue on the current TP.
27 */
28 csrrw tp, CSR_SCRATCH, tp
29 bnez tp, .Lsave_context
30
31.Lrestore_kernel_tpsp:
32 csrr tp, CSR_SCRATCH
33 REG_S sp, TASK_TI_KERNEL_SP(tp)
34
35#ifdef CONFIG_VMAP_STACK
36 addi sp, sp, -(PT_SIZE_ON_STACK)
37 srli sp, sp, THREAD_SHIFT
38 andi sp, sp, 0x1
39 bnez sp, handle_kernel_stack_overflow
40 REG_L sp, TASK_TI_KERNEL_SP(tp)
41#endif
42
43.Lsave_context:
44 REG_S sp, TASK_TI_USER_SP(tp)
45 REG_L sp, TASK_TI_KERNEL_SP(tp)
46 addi sp, sp, -(PT_SIZE_ON_STACK)
47 REG_S x1, PT_RA(sp)
48 REG_S x3, PT_GP(sp)
49 REG_S x5, PT_T0(sp)
50 save_from_x6_to_x31
51
52 /*
53 * Disable user-mode memory access as it should only be set in the
54 * actual user copy routines.
55 *
56 * Disable the FPU/Vector to detect illegal usage of floating point
57 * or vector in kernel space.
58 */
59 li t0, SR_SUM | SR_FS_VS
60
61 REG_L s0, TASK_TI_USER_SP(tp)
62 csrrc s1, CSR_STATUS, t0
63 csrr s2, CSR_EPC
64 csrr s3, CSR_TVAL
65 csrr s4, CSR_CAUSE
66 csrr s5, CSR_SCRATCH
67 REG_S s0, PT_SP(sp)
68 REG_S s1, PT_STATUS(sp)
69 REG_S s2, PT_EPC(sp)
70 REG_S s3, PT_BADADDR(sp)
71 REG_S s4, PT_CAUSE(sp)
72 REG_S s5, PT_TP(sp)
73
74 /*
75 * Set the scratch register to 0, so that if a recursive exception
76 * occurs, the exception vector knows it came from the kernel
77 */
78 csrw CSR_SCRATCH, x0
79
80 /* Load the global pointer */
81 load_global_pointer
82
83 /* Load the kernel shadow call stack pointer if coming from userspace */
84 scs_load_current_if_task_changed s5
85
86#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
87 move a0, sp
88 call riscv_v_context_nesting_start
89#endif
90 move a0, sp /* pt_regs */
91 la ra, ret_from_exception
92
93 /*
94 * MSB of cause differentiates between
95 * interrupts and exceptions
96 */
97 bge s4, zero, 1f
98
99 /* Handle interrupts */
100 tail do_irq
1011:
102 /* Handle other exceptions */
103 slli t0, s4, RISCV_LGPTR
104 la t1, excp_vect_table
105 la t2, excp_vect_table_end
106 add t0, t1, t0
107 /* Check if exception code lies within bounds */
108 bgeu t0, t2, 1f
109 REG_L t0, 0(t0)
110 jr t0
1111:
112 tail do_trap_unknown
113SYM_CODE_END(handle_exception)
114ASM_NOKPROBE(handle_exception)
115
116/*
117 * The ret_from_exception must be called with interrupt disabled. Here is the
118 * caller list:
119 * - handle_exception
120 * - ret_from_fork
121 */
122SYM_CODE_START_NOALIGN(ret_from_exception)
123 REG_L s0, PT_STATUS(sp)
124#ifdef CONFIG_RISCV_M_MODE
125 /* the MPP value is too large to be used as an immediate arg for addi */
126 li t0, SR_MPP
127 and s0, s0, t0
128#else
129 andi s0, s0, SR_SPP
130#endif
131 bnez s0, 1f
132
133 /* Save unwound kernel stack pointer in thread_info */
134 addi s0, sp, PT_SIZE_ON_STACK
135 REG_S s0, TASK_TI_KERNEL_SP(tp)
136
137 /* Save the kernel shadow call stack pointer */
138 scs_save_current
139
140 /*
141 * Save TP into the scratch register , so we can find the kernel data
142 * structures again.
143 */
144 csrw CSR_SCRATCH, tp
1451:
146#ifdef CONFIG_RISCV_ISA_V_PREEMPTIVE
147 move a0, sp
148 call riscv_v_context_nesting_end
149#endif
150 REG_L a0, PT_STATUS(sp)
151 /*
152 * The current load reservation is effectively part of the processor's
153 * state, in the sense that load reservations cannot be shared between
154 * different hart contexts. We can't actually save and restore a load
155 * reservation, so instead here we clear any existing reservation --
156 * it's always legal for implementations to clear load reservations at
157 * any point (as long as the forward progress guarantee is kept, but
158 * we'll ignore that here).
159 *
160 * Dangling load reservations can be the result of taking a trap in the
161 * middle of an LR/SC sequence, but can also be the result of a taken
162 * forward branch around an SC -- which is how we implement CAS. As a
163 * result we need to clear reservations between the last CAS and the
164 * jump back to the new context. While it is unlikely the store
165 * completes, implementations are allowed to expand reservations to be
166 * arbitrarily large.
167 */
168 REG_L a2, PT_EPC(sp)
169 REG_SC x0, a2, PT_EPC(sp)
170
171 csrw CSR_STATUS, a0
172 csrw CSR_EPC, a2
173
174 REG_L x1, PT_RA(sp)
175 REG_L x3, PT_GP(sp)
176 REG_L x4, PT_TP(sp)
177 REG_L x5, PT_T0(sp)
178 restore_from_x6_to_x31
179
180 REG_L x2, PT_SP(sp)
181
182#ifdef CONFIG_RISCV_M_MODE
183 mret
184#else
185 sret
186#endif
187SYM_CODE_END(ret_from_exception)
188ASM_NOKPROBE(ret_from_exception)
189
190#ifdef CONFIG_VMAP_STACK
191SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
192 /* we reach here from kernel context, sscratch must be 0 */
193 csrrw x31, CSR_SCRATCH, x31
194 asm_per_cpu sp, overflow_stack, x31
195 li x31, OVERFLOW_STACK_SIZE
196 add sp, sp, x31
197 /* zero out x31 again and restore x31 */
198 xor x31, x31, x31
199 csrrw x31, CSR_SCRATCH, x31
200
201 addi sp, sp, -(PT_SIZE_ON_STACK)
202
203 //save context to overflow stack
204 REG_S x1, PT_RA(sp)
205 REG_S x3, PT_GP(sp)
206 REG_S x5, PT_T0(sp)
207 save_from_x6_to_x31
208
209 REG_L s0, TASK_TI_KERNEL_SP(tp)
210 csrr s1, CSR_STATUS
211 csrr s2, CSR_EPC
212 csrr s3, CSR_TVAL
213 csrr s4, CSR_CAUSE
214 csrr s5, CSR_SCRATCH
215 REG_S s0, PT_SP(sp)
216 REG_S s1, PT_STATUS(sp)
217 REG_S s2, PT_EPC(sp)
218 REG_S s3, PT_BADADDR(sp)
219 REG_S s4, PT_CAUSE(sp)
220 REG_S s5, PT_TP(sp)
221 move a0, sp
222 tail handle_bad_stack
223SYM_CODE_END(handle_kernel_stack_overflow)
224ASM_NOKPROBE(handle_kernel_stack_overflow)
225#endif
226
227SYM_CODE_START(ret_from_fork)
228 call schedule_tail
229 beqz s0, 1f /* not from kernel thread */
230 /* Call fn(arg) */
231 move a0, s1
232 jalr s0
2331:
234 move a0, sp /* pt_regs */
235 la ra, ret_from_exception
236 tail syscall_exit_to_user_mode
237SYM_CODE_END(ret_from_fork)
238
239#ifdef CONFIG_IRQ_STACKS
240/*
241 * void call_on_irq_stack(struct pt_regs *regs,
242 * void (*func)(struct pt_regs *));
243 *
244 * Calls func(regs) using the per-CPU IRQ stack.
245 */
246SYM_FUNC_START(call_on_irq_stack)
247 /* Create a frame record to save ra and s0 (fp) */
248 addi sp, sp, -STACKFRAME_SIZE_ON_STACK
249 REG_S ra, STACKFRAME_RA(sp)
250 REG_S s0, STACKFRAME_FP(sp)
251 addi s0, sp, STACKFRAME_SIZE_ON_STACK
252
253 /* Switch to the per-CPU shadow call stack */
254 scs_save_current
255 scs_load_irq_stack t0
256
257 /* Switch to the per-CPU IRQ stack and call the handler */
258 load_per_cpu t0, irq_stack_ptr, t1
259 li t1, IRQ_STACK_SIZE
260 add sp, t0, t1
261 jalr a1
262
263 /* Switch back to the thread shadow call stack */
264 scs_load_current
265
266 /* Switch back to the thread stack and restore ra and s0 */
267 addi sp, s0, -STACKFRAME_SIZE_ON_STACK
268 REG_L ra, STACKFRAME_RA(sp)
269 REG_L s0, STACKFRAME_FP(sp)
270 addi sp, sp, STACKFRAME_SIZE_ON_STACK
271
272 ret
273SYM_FUNC_END(call_on_irq_stack)
274#endif /* CONFIG_IRQ_STACKS */
275
276/*
277 * Integer register context switch
278 * The callee-saved registers must be saved and restored.
279 *
280 * a0: previous task_struct (must be preserved across the switch)
281 * a1: next task_struct
282 *
283 * The value of a0 and a1 must be preserved by this function, as that's how
284 * arguments are passed to schedule_tail.
285 */
286SYM_FUNC_START(__switch_to)
287 /* Save context into prev->thread */
288 li a4, TASK_THREAD_RA
289 add a3, a0, a4
290 add a4, a1, a4
291 REG_S ra, TASK_THREAD_RA_RA(a3)
292 REG_S sp, TASK_THREAD_SP_RA(a3)
293 REG_S s0, TASK_THREAD_S0_RA(a3)
294 REG_S s1, TASK_THREAD_S1_RA(a3)
295 REG_S s2, TASK_THREAD_S2_RA(a3)
296 REG_S s3, TASK_THREAD_S3_RA(a3)
297 REG_S s4, TASK_THREAD_S4_RA(a3)
298 REG_S s5, TASK_THREAD_S5_RA(a3)
299 REG_S s6, TASK_THREAD_S6_RA(a3)
300 REG_S s7, TASK_THREAD_S7_RA(a3)
301 REG_S s8, TASK_THREAD_S8_RA(a3)
302 REG_S s9, TASK_THREAD_S9_RA(a3)
303 REG_S s10, TASK_THREAD_S10_RA(a3)
304 REG_S s11, TASK_THREAD_S11_RA(a3)
305 /* Save the kernel shadow call stack pointer */
306 scs_save_current
307 /* Restore context from next->thread */
308 REG_L ra, TASK_THREAD_RA_RA(a4)
309 REG_L sp, TASK_THREAD_SP_RA(a4)
310 REG_L s0, TASK_THREAD_S0_RA(a4)
311 REG_L s1, TASK_THREAD_S1_RA(a4)
312 REG_L s2, TASK_THREAD_S2_RA(a4)
313 REG_L s3, TASK_THREAD_S3_RA(a4)
314 REG_L s4, TASK_THREAD_S4_RA(a4)
315 REG_L s5, TASK_THREAD_S5_RA(a4)
316 REG_L s6, TASK_THREAD_S6_RA(a4)
317 REG_L s7, TASK_THREAD_S7_RA(a4)
318 REG_L s8, TASK_THREAD_S8_RA(a4)
319 REG_L s9, TASK_THREAD_S9_RA(a4)
320 REG_L s10, TASK_THREAD_S10_RA(a4)
321 REG_L s11, TASK_THREAD_S11_RA(a4)
322 /* The offset of thread_info in task_struct is zero. */
323 move tp, a1
324 /* Switch to the next shadow call stack */
325 scs_load_current
326 ret
327SYM_FUNC_END(__switch_to)
328
329#ifndef CONFIG_MMU
330#define do_page_fault do_trap_unknown
331#endif
332
333 .section ".rodata"
334 .align LGREG
335 /* Exception vector table */
336SYM_DATA_START_LOCAL(excp_vect_table)
337 RISCV_PTR do_trap_insn_misaligned
338 ALT_INSN_FAULT(RISCV_PTR do_trap_insn_fault)
339 RISCV_PTR do_trap_insn_illegal
340 RISCV_PTR do_trap_break
341 RISCV_PTR do_trap_load_misaligned
342 RISCV_PTR do_trap_load_fault
343 RISCV_PTR do_trap_store_misaligned
344 RISCV_PTR do_trap_store_fault
345 RISCV_PTR do_trap_ecall_u /* system call */
346 RISCV_PTR do_trap_ecall_s
347 RISCV_PTR do_trap_unknown
348 RISCV_PTR do_trap_ecall_m
349 /* instruciton page fault */
350 ALT_PAGE_FAULT(RISCV_PTR do_page_fault)
351 RISCV_PTR do_page_fault /* load page fault */
352 RISCV_PTR do_trap_unknown
353 RISCV_PTR do_page_fault /* store page fault */
354SYM_DATA_END_LABEL(excp_vect_table, SYM_L_LOCAL, excp_vect_table_end)
355
356#ifndef CONFIG_MMU
357SYM_DATA_START(__user_rt_sigreturn)
358 li a7, __NR_rt_sigreturn
359 ecall
360SYM_DATA_END(__user_rt_sigreturn)
361#endif
362

source code of linux/arch/riscv/kernel/entry.S