1// SPDX-License-Identifier: GPL-2.0
2// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
3
4#include <linux/extable.h>
5#include <linux/kprobes.h>
6#include <linux/mmu_context.h>
7#include <linux/perf_event.h>
8
9int fixup_exception(struct pt_regs *regs)
10{
11	const struct exception_table_entry *fixup;
12
13	fixup = search_exception_tables(instruction_pointer(regs));
14	if (fixup) {
15		regs->pc = fixup->fixup;
16
17		return 1;
18	}
19
20	return 0;
21}
22
23static inline bool is_write(struct pt_regs *regs)
24{
25	switch (trap_no(regs)) {
26	case VEC_TLBINVALIDS:
27		return true;
28	case VEC_TLBMODIFIED:
29		return true;
30	}
31
32	return false;
33}
34
35#ifdef CONFIG_CPU_HAS_LDSTEX
36static inline void csky_cmpxchg_fixup(struct pt_regs *regs)
37{
38	return;
39}
40#else
41extern unsigned long csky_cmpxchg_ldw;
42extern unsigned long csky_cmpxchg_stw;
43static inline void csky_cmpxchg_fixup(struct pt_regs *regs)
44{
45	if (trap_no(regs) != VEC_TLBMODIFIED)
46		return;
47
48	if (instruction_pointer(regs) == csky_cmpxchg_stw)
49		instruction_pointer_set(regs, csky_cmpxchg_ldw);
50	return;
51}
52#endif
53
54static inline void no_context(struct pt_regs *regs, unsigned long addr)
55{
56	current->thread.trap_no = trap_no(regs);
57
58	/* Are we prepared to handle this kernel fault? */
59	if (fixup_exception(regs))
60		return;
61
62	/*
63	 * Oops. The kernel tried to access some bad page. We'll have to
64	 * terminate things with extreme prejudice.
65	 */
66	bust_spinlocks(1);
67	pr_alert("Unable to handle kernel paging request at virtual "
68		 "addr 0x%08lx, pc: 0x%08lx\n", addr, regs->pc);
69	die(regs, "Oops");
70	make_task_dead(SIGKILL);
71}
72
73static inline void mm_fault_error(struct pt_regs *regs, unsigned long addr, vm_fault_t fault)
74{
75	current->thread.trap_no = trap_no(regs);
76
77	if (fault & VM_FAULT_OOM) {
78		/*
79		 * We ran out of memory, call the OOM killer, and return the userspace
80		 * (which will retry the fault, or kill us if we got oom-killed).
81		 */
82		if (!user_mode(regs)) {
83			no_context(regs, addr);
84			return;
85		}
86		pagefault_out_of_memory();
87		return;
88	} else if (fault & VM_FAULT_SIGBUS) {
89		/* Kernel mode? Handle exceptions or die */
90		if (!user_mode(regs)) {
91			no_context(regs, addr);
92			return;
93		}
94		do_trap(regs, SIGBUS, BUS_ADRERR, addr);
95		return;
96	}
97	BUG();
98}
99
100static inline void bad_area_nosemaphore(struct pt_regs *regs, struct mm_struct *mm, int code, unsigned long addr)
101{
102	/*
103	 * Something tried to access memory that isn't in our memory map.
104	 * Fix it, but check if it's kernel or user first.
105	 */
106	/* User mode accesses just cause a SIGSEGV */
107	if (user_mode(regs)) {
108		do_trap(regs, SIGSEGV, code, addr);
109		return;
110	}
111
112	no_context(regs, addr);
113}
114
115static inline void vmalloc_fault(struct pt_regs *regs, int code, unsigned long addr)
116{
117	pgd_t *pgd, *pgd_k;
118	pud_t *pud, *pud_k;
119	pmd_t *pmd, *pmd_k;
120	pte_t *pte_k;
121	int offset;
122
123	/* User mode accesses just cause a SIGSEGV */
124	if (user_mode(regs)) {
125		do_trap(regs, SIGSEGV, code, addr);
126		return;
127	}
128
129	/*
130	 * Synchronize this task's top level page-table
131	 * with the 'reference' page table.
132	 *
133	 * Do _not_ use "tsk" here. We might be inside
134	 * an interrupt in the middle of a task switch..
135	 */
136	offset = pgd_index(addr);
137
138	pgd = get_pgd() + offset;
139	pgd_k = init_mm.pgd + offset;
140
141	if (!pgd_present(*pgd_k)) {
142		no_context(regs, addr);
143		return;
144	}
145	set_pgd(pgd, *pgd_k);
146
147	pud = (pud_t *)pgd;
148	pud_k = (pud_t *)pgd_k;
149	if (!pud_present(*pud_k)) {
150		no_context(regs, addr);
151		return;
152	}
153
154	pmd = pmd_offset(pud, addr);
155	pmd_k = pmd_offset(pud_k, addr);
156	if (!pmd_present(*pmd_k)) {
157		no_context(regs, addr);
158		return;
159	}
160	set_pmd(pmd, *pmd_k);
161
162	pte_k = pte_offset_kernel(pmd_k, addr);
163	if (!pte_present(*pte_k)) {
164		no_context(regs, addr);
165		return;
166	}
167
168	flush_tlb_one(addr);
169}
170
171static inline bool access_error(struct pt_regs *regs, struct vm_area_struct *vma)
172{
173	if (is_write(regs)) {
174		if (!(vma->vm_flags & VM_WRITE))
175			return true;
176	} else {
177		if (unlikely(!vma_is_accessible(vma)))
178			return true;
179	}
180	return false;
181}
182
183/*
184 * This routine handles page faults.  It determines the address and the
185 * problem, and then passes it off to one of the appropriate routines.
186 */
187asmlinkage void do_page_fault(struct pt_regs *regs)
188{
189	struct task_struct *tsk;
190	struct vm_area_struct *vma;
191	struct mm_struct *mm;
192	unsigned long addr = read_mmu_entryhi() & PAGE_MASK;
193	unsigned int flags = FAULT_FLAG_DEFAULT;
194	int code = SEGV_MAPERR;
195	vm_fault_t fault;
196
197	tsk = current;
198	mm = tsk->mm;
199
200	csky_cmpxchg_fixup(regs);
201
202	if (kprobe_page_fault(regs, tsk->thread.trap_no))
203		return;
204
205	/*
206	 * Fault-in kernel-space virtual memory on-demand.
207	 * The 'reference' page table is init_mm.pgd.
208	 *
209	 * NOTE! We MUST NOT take any locks for this case. We may
210	 * be in an interrupt or a critical region, and should
211	 * only copy the information from the master page table,
212	 * nothing more.
213	 */
214	if (unlikely((addr >= VMALLOC_START) && (addr <= VMALLOC_END))) {
215		vmalloc_fault(regs, code, addr);
216		return;
217	}
218
219	/* Enable interrupts if they were enabled in the parent context. */
220	if (likely(regs->sr & BIT(6)))
221		local_irq_enable();
222
223	/*
224	 * If we're in an interrupt, have no user context, or are running
225	 * in an atomic region, then we must not take the fault.
226	 */
227	if (unlikely(faulthandler_disabled() || !mm)) {
228		no_context(regs, addr);
229		return;
230	}
231
232	if (user_mode(regs))
233		flags |= FAULT_FLAG_USER;
234
235	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
236
237	if (is_write(regs))
238		flags |= FAULT_FLAG_WRITE;
239retry:
240	vma = lock_mm_and_find_vma(mm, addr, regs);
241	if (unlikely(!vma)) {
242		bad_area_nosemaphore(regs, mm, code, addr);
243		return;
244	}
245
246	/*
247	 * Ok, we have a good vm_area for this memory access, so
248	 * we can handle it.
249	 */
250	code = SEGV_ACCERR;
251
252	if (unlikely(access_error(regs, vma))) {
253		mmap_read_unlock(mm);
254		bad_area_nosemaphore(regs, mm, code, addr);
255		return;
256	}
257
258	/*
259	 * If for any reason at all we could not handle the fault,
260	 * make sure we exit gracefully rather than endlessly redo
261	 * the fault.
262	 */
263	fault = handle_mm_fault(vma, addr, flags, regs);
264
265	/*
266	 * If we need to retry but a fatal signal is pending, handle the
267	 * signal first. We do not need to release the mmap_lock because it
268	 * would already be released in __lock_page_or_retry in mm/filemap.c.
269	 */
270	if (fault_signal_pending(fault, regs)) {
271		if (!user_mode(regs))
272			no_context(regs, addr);
273		return;
274	}
275
276	/* The fault is fully completed (including releasing mmap lock) */
277	if (fault & VM_FAULT_COMPLETED)
278		return;
279
280	if (unlikely((fault & VM_FAULT_RETRY) && (flags & FAULT_FLAG_ALLOW_RETRY))) {
281		flags |= FAULT_FLAG_TRIED;
282
283		/*
284		 * No need to mmap_read_unlock(mm) as we would
285		 * have already released it in __lock_page_or_retry
286		 * in mm/filemap.c.
287		 */
288		goto retry;
289	}
290
291	mmap_read_unlock(mm);
292
293	if (unlikely(fault & VM_FAULT_ERROR)) {
294		mm_fault_error(regs, addr, fault);
295		return;
296	}
297	return;
298}
299