| blob | 208702d8c18eeac291ca8ef21eeec977d93af570 |
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 */
7 #include <linux/init.h>
8 #include <linux/linkage.h>
10 #include <asm/asm.h>
11 #include <asm/csr.h>
12 #include <asm/unistd.h>
13 #include <asm/thread_info.h>
14 #include <asm/asm-offsets.h>
16 .text
17 .altmacro
19 /*
20 * Prepares to enter a system call or exception by saving all registers to the
21 * stack.
22 */
23 .macro SAVE_ALL
24 LOCAL _restore_kernel_tpsp
25 LOCAL _save_context
27 /*
28 * If coming from userspace, preserve the user thread pointer and load
29 * the kernel thread pointer. If we came from the kernel, the scratch
30 * register will contain 0, and we should continue on the current TP.
31 */
32 csrrw tp, CSR_SCRATCH, tp
33 bnez tp, _save_context
35 _restore_kernel_tpsp:
36 csrr tp, CSR_SCRATCH
37 REG_S sp, TASK_TI_KERNEL_SP(tp)
38 _save_context:
39 REG_S sp, TASK_TI_USER_SP(tp)
40 REG_L sp, TASK_TI_KERNEL_SP(tp)
41 addi sp, sp, -(PT_SIZE_ON_STACK)
42 REG_S x1, PT_RA(sp)
43 REG_S x3, PT_GP(sp)
44 REG_S x5, PT_T0(sp)
45 REG_S x6, PT_T1(sp)
46 REG_S x7, PT_T2(sp)
47 REG_S x8, PT_S0(sp)
48 REG_S x9, PT_S1(sp)
49 REG_S x10, PT_A0(sp)
50 REG_S x11, PT_A1(sp)
51 REG_S x12, PT_A2(sp)
52 REG_S x13, PT_A3(sp)
53 REG_S x14, PT_A4(sp)
54 REG_S x15, PT_A5(sp)
55 REG_S x16, PT_A6(sp)
56 REG_S x17, PT_A7(sp)
57 REG_S x18, PT_S2(sp)
58 REG_S x19, PT_S3(sp)
59 REG_S x20, PT_S4(sp)
60 REG_S x21, PT_S5(sp)
61 REG_S x22, PT_S6(sp)
62 REG_S x23, PT_S7(sp)
63 REG_S x24, PT_S8(sp)
64 REG_S x25, PT_S9(sp)
65 REG_S x26, PT_S10(sp)
66 REG_S x27, PT_S11(sp)
67 REG_S x28, PT_T3(sp)
68 REG_S x29, PT_T4(sp)
69 REG_S x30, PT_T5(sp)
70 REG_S x31, PT_T6(sp)
72 /*
73 * Disable user-mode memory access as it should only be set in the
74 * actual user copy routines.
75 *
76 * Disable the FPU to detect illegal usage of floating point in kernel
77 * space.
78 */
79 li t0, SR_SUM | SR_FS
81 REG_L s0, TASK_TI_USER_SP(tp)
82 csrrc s1, CSR_STATUS, t0
83 csrr s2, CSR_EPC
84 csrr s3, CSR_TVAL
85 csrr s4, CSR_CAUSE
86 csrr s5, CSR_SCRATCH
87 REG_S s0, PT_SP(sp)
88 REG_S s1, PT_STATUS(sp)
89 REG_S s2, PT_EPC(sp)
90 REG_S s3, PT_BADADDR(sp)
91 REG_S s4, PT_CAUSE(sp)
92 REG_S s5, PT_TP(sp)
93 .endm
95 /*
96 * Prepares to return from a system call or exception by restoring all
97 * registers from the stack.
98 */
99 .macro RESTORE_ALL
100 REG_L a0, PT_STATUS(sp)
101 /*
102 * The current load reservation is effectively part of the processor's
103 * state, in the sense that load reservations cannot be shared between
104 * different hart contexts. We can't actually save and restore a load
105 * reservation, so instead here we clear any existing reservation --
106 * it's always legal for implementations to clear load reservations at
107 * any point (as long as the forward progress guarantee is kept, but
108 * we'll ignore that here).
109 *
110 * Dangling load reservations can be the result of taking a trap in the
111 * middle of an LR/SC sequence, but can also be the result of a taken
112 * forward branch around an SC -- which is how we implement CAS. As a
113 * result we need to clear reservations between the last CAS and the
114 * jump back to the new context. While it is unlikely the store
115 * completes, implementations are allowed to expand reservations to be
116 * arbitrarily large.
117 */
118 REG_L a2, PT_EPC(sp)
119 REG_SC x0, a2, PT_EPC(sp)
121 csrw CSR_STATUS, a0
122 csrw CSR_EPC, a2
124 REG_L x1, PT_RA(sp)
125 REG_L x3, PT_GP(sp)
126 REG_L x4, PT_TP(sp)
127 REG_L x5, PT_T0(sp)
128 REG_L x6, PT_T1(sp)
129 REG_L x7, PT_T2(sp)
130 REG_L x8, PT_S0(sp)
131 REG_L x9, PT_S1(sp)
132 REG_L x10, PT_A0(sp)
133 REG_L x11, PT_A1(sp)
134 REG_L x12, PT_A2(sp)
135 REG_L x13, PT_A3(sp)
136 REG_L x14, PT_A4(sp)
137 REG_L x15, PT_A5(sp)
138 REG_L x16, PT_A6(sp)
139 REG_L x17, PT_A7(sp)
140 REG_L x18, PT_S2(sp)
141 REG_L x19, PT_S3(sp)
142 REG_L x20, PT_S4(sp)
143 REG_L x21, PT_S5(sp)
144 REG_L x22, PT_S6(sp)
145 REG_L x23, PT_S7(sp)
146 REG_L x24, PT_S8(sp)
147 REG_L x25, PT_S9(sp)
148 REG_L x26, PT_S10(sp)
149 REG_L x27, PT_S11(sp)
150 REG_L x28, PT_T3(sp)
151 REG_L x29, PT_T4(sp)
152 REG_L x30, PT_T5(sp)
153 REG_L x31, PT_T6(sp)
155 REG_L x2, PT_SP(sp)
156 .endm
158 #if !IS_ENABLED(CONFIG_PREEMPTION)
159 .set resume_kernel, restore_all
160 #endif
162 ENTRY(handle_exception)
163 SAVE_ALL
165 /*
166 * Set the scratch register to 0, so that if a recursive exception
167 * occurs, the exception vector knows it came from the kernel
168 */
169 csrw CSR_SCRATCH, x0
171 /* Load the global pointer */
172 .option push
173 .option norelax
174 la gp, __global_pointer$
175 .option pop
177 la ra, ret_from_exception
178 /*
179 * MSB of cause differentiates between
180 * interrupts and exceptions
181 */
182 bge s4, zero, 1f
184 /* Handle interrupts */
185 move a0, sp /* pt_regs */
186 tail do_IRQ
187 1:
188 /*
189 * Exceptions run with interrupts enabled or disabled depending on the
190 * state of SR_PIE in m/sstatus.
191 */
192 andi t0, s1, SR_PIE
193 beqz t0, 1f
194 csrs CSR_STATUS, SR_IE
196 1:
197 /* Handle syscalls */
198 li t0, EXC_SYSCALL
199 beq s4, t0, handle_syscall
201 /* Handle other exceptions */
202 slli t0, s4, RISCV_LGPTR
203 la t1, excp_vect_table
204 la t2, excp_vect_table_end
205 move a0, sp /* pt_regs */
206 add t0, t1, t0
207 /* Check if exception code lies within bounds */
208 bgeu t0, t2, 1f
209 REG_L t0, 0(t0)
210 jr t0
211 1:
212 tail do_trap_unknown
214 handle_syscall:
215 /* save the initial A0 value (needed in signal handlers) */
216 REG_S a0, PT_ORIG_A0(sp)
217 /*
218 * Advance SEPC to avoid executing the original
219 * scall instruction on sret
220 */
221 addi s2, s2, 0x4
222 REG_S s2, PT_EPC(sp)
223 /* Trace syscalls, but only if requested by the user. */
224 REG_L t0, TASK_TI_FLAGS(tp)
225 andi t0, t0, _TIF_SYSCALL_WORK
226 bnez t0, handle_syscall_trace_enter
227 check_syscall_nr:
228 /* Check to make sure we don't jump to a bogus syscall number. */
229 li t0, __NR_syscalls
230 la s0, sys_ni_syscall
231 /*
232 * Syscall number held in a7.
233 * If syscall number is above allowed value, redirect to ni_syscall.
234 */
235 bge a7, t0, 1f
236 /*
237 * Check if syscall is rejected by tracer, i.e., a7 == -1.
238 * If yes, we pretend it was executed.
239 */
240 li t1, -1
241 beq a7, t1, ret_from_syscall_rejected
242 blt a7, t1, 1f
243 /* Call syscall */
244 la s0, sys_call_table
245 slli t0, a7, RISCV_LGPTR
246 add s0, s0, t0
247 REG_L s0, 0(s0)
248 1:
249 jalr s0
251 ret_from_syscall:
252 /* Set user a0 to kernel a0 */
253 REG_S a0, PT_A0(sp)
254 /*
255 * We didn't execute the actual syscall.
256 * Seccomp already set return value for the current task pt_regs.
257 * (If it was configured with SECCOMP_RET_ERRNO/TRACE)
258 */
259 ret_from_syscall_rejected:
260 /* Trace syscalls, but only if requested by the user. */
261 REG_L t0, TASK_TI_FLAGS(tp)
262 andi t0, t0, _TIF_SYSCALL_WORK
263 bnez t0, handle_syscall_trace_exit
265 ret_from_exception:
266 REG_L s0, PT_STATUS(sp)
267 csrc CSR_STATUS, SR_IE
268 #ifdef CONFIG_RISCV_M_MODE
269 /* the MPP value is too large to be used as an immediate arg for addi */
270 li t0, SR_MPP
271 and s0, s0, t0
272 #else
273 andi s0, s0, SR_SPP
274 #endif
275 bnez s0, resume_kernel
277 resume_userspace:
278 /* Interrupts must be disabled here so flags are checked atomically */
279 REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
280 andi s1, s0, _TIF_WORK_MASK
281 bnez s1, work_pending
283 /* Save unwound kernel stack pointer in thread_info */
284 addi s0, sp, PT_SIZE_ON_STACK
285 REG_S s0, TASK_TI_KERNEL_SP(tp)
287 /*
288 * Save TP into the scratch register , so we can find the kernel data
289 * structures again.
290 */
291 csrw CSR_SCRATCH, tp
293 restore_all:
294 RESTORE_ALL
295 #ifdef CONFIG_RISCV_M_MODE
296 mret
297 #else
298 sret
299 #endif
301 #if IS_ENABLED(CONFIG_PREEMPTION)
302 resume_kernel:
303 REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
304 bnez s0, restore_all
305 REG_L s0, TASK_TI_FLAGS(tp)
306 andi s0, s0, _TIF_NEED_RESCHED
307 beqz s0, restore_all
308 call preempt_schedule_irq
309 j restore_all
310 #endif
312 work_pending:
313 /* Enter slow path for supplementary processing */
314 la ra, ret_from_exception
315 andi s1, s0, _TIF_NEED_RESCHED
316 bnez s1, work_resched
317 work_notifysig:
318 /* Handle pending signals and notify-resume requests */
319 csrs CSR_STATUS, SR_IE /* Enable interrupts for do_notify_resume() */
320 move a0, sp /* pt_regs */
321 move a1, s0 /* current_thread_info->flags */
322 tail do_notify_resume
323 work_resched:
324 tail schedule
326 /* Slow paths for ptrace. */
327 handle_syscall_trace_enter:
328 move a0, sp
329 call do_syscall_trace_enter
330 move t0, a0
331 REG_L a0, PT_A0(sp)
332 REG_L a1, PT_A1(sp)
333 REG_L a2, PT_A2(sp)
334 REG_L a3, PT_A3(sp)
335 REG_L a4, PT_A4(sp)
336 REG_L a5, PT_A5(sp)
337 REG_L a6, PT_A6(sp)
338 REG_L a7, PT_A7(sp)
339 bnez t0, ret_from_syscall_rejected
340 j check_syscall_nr
341 handle_syscall_trace_exit:
342 move a0, sp
343 call do_syscall_trace_exit
344 j ret_from_exception
346 END(handle_exception)
348 ENTRY(ret_from_fork)
349 la ra, ret_from_exception
350 tail schedule_tail
351 ENDPROC(ret_from_fork)
353 ENTRY(ret_from_kernel_thread)
354 call schedule_tail
355 /* Call fn(arg) */
356 la ra, ret_from_exception
357 move a0, s1
358 jr s0
359 ENDPROC(ret_from_kernel_thread)
362 /*
363 * Integer register context switch
364 * The callee-saved registers must be saved and restored.
365 *
366 * a0: previous task_struct (must be preserved across the switch)
367 * a1: next task_struct
368 *
369 * The value of a0 and a1 must be preserved by this function, as that's how
370 * arguments are passed to schedule_tail.
371 */
372 ENTRY(__switch_to)
373 /* Save context into prev->thread */
374 li a4, TASK_THREAD_RA
375 add a3, a0, a4
376 add a4, a1, a4
377 REG_S ra, TASK_THREAD_RA_RA(a3)
378 REG_S sp, TASK_THREAD_SP_RA(a3)
379 REG_S s0, TASK_THREAD_S0_RA(a3)
380 REG_S s1, TASK_THREAD_S1_RA(a3)
381 REG_S s2, TASK_THREAD_S2_RA(a3)
382 REG_S s3, TASK_THREAD_S3_RA(a3)
383 REG_S s4, TASK_THREAD_S4_RA(a3)
384 REG_S s5, TASK_THREAD_S5_RA(a3)
385 REG_S s6, TASK_THREAD_S6_RA(a3)
386 REG_S s7, TASK_THREAD_S7_RA(a3)
387 REG_S s8, TASK_THREAD_S8_RA(a3)
388 REG_S s9, TASK_THREAD_S9_RA(a3)
389 REG_S s10, TASK_THREAD_S10_RA(a3)
390 REG_S s11, TASK_THREAD_S11_RA(a3)
391 /* Restore context from next->thread */
392 REG_L ra, TASK_THREAD_RA_RA(a4)
393 REG_L sp, TASK_THREAD_SP_RA(a4)
394 REG_L s0, TASK_THREAD_S0_RA(a4)
395 REG_L s1, TASK_THREAD_S1_RA(a4)
396 REG_L s2, TASK_THREAD_S2_RA(a4)
397 REG_L s3, TASK_THREAD_S3_RA(a4)
398 REG_L s4, TASK_THREAD_S4_RA(a4)
399 REG_L s5, TASK_THREAD_S5_RA(a4)
400 REG_L s6, TASK_THREAD_S6_RA(a4)
401 REG_L s7, TASK_THREAD_S7_RA(a4)
402 REG_L s8, TASK_THREAD_S8_RA(a4)
403 REG_L s9, TASK_THREAD_S9_RA(a4)
404 REG_L s10, TASK_THREAD_S10_RA(a4)
405 REG_L s11, TASK_THREAD_S11_RA(a4)
406 /* Swap the CPU entry around. */
407 lw a3, TASK_TI_CPU(a0)
408 lw a4, TASK_TI_CPU(a1)
409 sw a3, TASK_TI_CPU(a1)
410 sw a4, TASK_TI_CPU(a0)
411 #if TASK_TI != 0
412 #error "TASK_TI != 0: tp will contain a 'struct thread_info', not a 'struct task_struct' so get_current() won't work."
413 addi tp, a1, TASK_TI
414 #else
415 move tp, a1
416 #endif
417 ret
418 ENDPROC(__switch_to)
420 #ifndef CONFIG_MMU
421 #define do_page_fault do_trap_unknown
422 #endif
424 .section ".rodata"
425 /* Exception vector table */
426 ENTRY(excp_vect_table)
427 RISCV_PTR do_trap_insn_misaligned
428 RISCV_PTR do_trap_insn_fault
429 RISCV_PTR do_trap_insn_illegal
430 RISCV_PTR do_trap_break
431 RISCV_PTR do_trap_load_misaligned
432 RISCV_PTR do_trap_load_fault
433 RISCV_PTR do_trap_store_misaligned
434 RISCV_PTR do_trap_store_fault
435 RISCV_PTR do_trap_ecall_u /* system call, gets intercepted */
436 RISCV_PTR do_trap_ecall_s
437 RISCV_PTR do_trap_unknown
438 RISCV_PTR do_trap_ecall_m
439 RISCV_PTR do_page_fault /* instruction page fault */
440 RISCV_PTR do_page_fault /* load page fault */
441 RISCV_PTR do_trap_unknown
442 RISCV_PTR do_page_fault /* store page fault */
443 excp_vect_table_end:
444 END(excp_vect_table)
446 #ifndef CONFIG_MMU
447 ENTRY(__user_rt_sigreturn)
448 li a7, __NR_rt_sigreturn
449 scall
450 END(__user_rt_sigreturn)
451 #endif