xref: /openbmc/linux/arch/powerpc/mm/pgtable.c (revision e8f6f3b4)
1 /*
2  * This file contains common routines for dealing with free of page tables
3  * Along with common page table handling code
4  *
5  *  Derived from arch/powerpc/mm/tlb_64.c:
6  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
7  *
8  *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
9  *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
10  *    Copyright (C) 1996 Paul Mackerras
11  *
12  *  Derived from "arch/i386/mm/init.c"
13  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
14  *
15  *  Dave Engebretsen <engebret@us.ibm.com>
16  *      Rework for PPC64 port.
17  *
18  *  This program is free software; you can redistribute it and/or
19  *  modify it under the terms of the GNU General Public License
20  *  as published by the Free Software Foundation; either version
21  *  2 of the License, or (at your option) any later version.
22  */
23 
24 #include <linux/kernel.h>
25 #include <linux/gfp.h>
26 #include <linux/mm.h>
27 #include <linux/percpu.h>
28 #include <linux/hardirq.h>
29 #include <linux/hugetlb.h>
30 #include <asm/pgalloc.h>
31 #include <asm/tlbflush.h>
32 #include <asm/tlb.h>
33 
34 static inline int is_exec_fault(void)
35 {
36 	return current->thread.regs && TRAP(current->thread.regs) == 0x400;
37 }
38 
39 /* We only try to do i/d cache coherency on stuff that looks like
40  * reasonably "normal" PTEs. We currently require a PTE to be present
41  * and we avoid _PAGE_SPECIAL and _PAGE_NO_CACHE. We also only do that
42  * on userspace PTEs
43  */
44 static inline int pte_looks_normal(pte_t pte)
45 {
46 	return (pte_val(pte) &
47 	    (_PAGE_PRESENT | _PAGE_SPECIAL | _PAGE_NO_CACHE | _PAGE_USER)) ==
48 	    (_PAGE_PRESENT | _PAGE_USER);
49 }
50 
51 static struct page *maybe_pte_to_page(pte_t pte)
52 {
53 	unsigned long pfn = pte_pfn(pte);
54 	struct page *page;
55 
56 	if (unlikely(!pfn_valid(pfn)))
57 		return NULL;
58 	page = pfn_to_page(pfn);
59 	if (PageReserved(page))
60 		return NULL;
61 	return page;
62 }
63 
64 #if defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0
65 
66 /* Server-style MMU handles coherency when hashing if HW exec permission
67  * is supposed per page (currently 64-bit only). If not, then, we always
68  * flush the cache for valid PTEs in set_pte. Embedded CPU without HW exec
69  * support falls into the same category.
70  */
71 
72 static pte_t set_pte_filter(pte_t pte)
73 {
74 	pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
75 	if (pte_looks_normal(pte) && !(cpu_has_feature(CPU_FTR_COHERENT_ICACHE) ||
76 				       cpu_has_feature(CPU_FTR_NOEXECUTE))) {
77 		struct page *pg = maybe_pte_to_page(pte);
78 		if (!pg)
79 			return pte;
80 		if (!test_bit(PG_arch_1, &pg->flags)) {
81 			flush_dcache_icache_page(pg);
82 			set_bit(PG_arch_1, &pg->flags);
83 		}
84 	}
85 	return pte;
86 }
87 
88 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
89 				     int dirty)
90 {
91 	return pte;
92 }
93 
94 #else /* defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0 */
95 
96 /* Embedded type MMU with HW exec support. This is a bit more complicated
97  * as we don't have two bits to spare for _PAGE_EXEC and _PAGE_HWEXEC so
98  * instead we "filter out" the exec permission for non clean pages.
99  */
100 static pte_t set_pte_filter(pte_t pte)
101 {
102 	struct page *pg;
103 
104 	/* No exec permission in the first place, move on */
105 	if (!(pte_val(pte) & _PAGE_EXEC) || !pte_looks_normal(pte))
106 		return pte;
107 
108 	/* If you set _PAGE_EXEC on weird pages you're on your own */
109 	pg = maybe_pte_to_page(pte);
110 	if (unlikely(!pg))
111 		return pte;
112 
113 	/* If the page clean, we move on */
114 	if (test_bit(PG_arch_1, &pg->flags))
115 		return pte;
116 
117 	/* If it's an exec fault, we flush the cache and make it clean */
118 	if (is_exec_fault()) {
119 		flush_dcache_icache_page(pg);
120 		set_bit(PG_arch_1, &pg->flags);
121 		return pte;
122 	}
123 
124 	/* Else, we filter out _PAGE_EXEC */
125 	return __pte(pte_val(pte) & ~_PAGE_EXEC);
126 }
127 
128 static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
129 				     int dirty)
130 {
131 	struct page *pg;
132 
133 	/* So here, we only care about exec faults, as we use them
134 	 * to recover lost _PAGE_EXEC and perform I$/D$ coherency
135 	 * if necessary. Also if _PAGE_EXEC is already set, same deal,
136 	 * we just bail out
137 	 */
138 	if (dirty || (pte_val(pte) & _PAGE_EXEC) || !is_exec_fault())
139 		return pte;
140 
141 #ifdef CONFIG_DEBUG_VM
142 	/* So this is an exec fault, _PAGE_EXEC is not set. If it was
143 	 * an error we would have bailed out earlier in do_page_fault()
144 	 * but let's make sure of it
145 	 */
146 	if (WARN_ON(!(vma->vm_flags & VM_EXEC)))
147 		return pte;
148 #endif /* CONFIG_DEBUG_VM */
149 
150 	/* If you set _PAGE_EXEC on weird pages you're on your own */
151 	pg = maybe_pte_to_page(pte);
152 	if (unlikely(!pg))
153 		goto bail;
154 
155 	/* If the page is already clean, we move on */
156 	if (test_bit(PG_arch_1, &pg->flags))
157 		goto bail;
158 
159 	/* Clean the page and set PG_arch_1 */
160 	flush_dcache_icache_page(pg);
161 	set_bit(PG_arch_1, &pg->flags);
162 
163  bail:
164 	return __pte(pte_val(pte) | _PAGE_EXEC);
165 }
166 
167 #endif /* !(defined(CONFIG_PPC_STD_MMU) || _PAGE_EXEC == 0) */
168 
169 /*
170  * set_pte stores a linux PTE into the linux page table.
171  */
172 void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
173 		pte_t pte)
174 {
175 #ifdef CONFIG_DEBUG_VM
176 	WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
177 #endif
178 	/* Note: mm->context.id might not yet have been assigned as
179 	 * this context might not have been activated yet when this
180 	 * is called.
181 	 */
182 	pte = set_pte_filter(pte);
183 
184 	/* Perform the setting of the PTE */
185 	__set_pte_at(mm, addr, ptep, pte, 0);
186 }
187 
188 /*
189  * This is called when relaxing access to a PTE. It's also called in the page
190  * fault path when we don't hit any of the major fault cases, ie, a minor
191  * update of _PAGE_ACCESSED, _PAGE_DIRTY, etc... The generic code will have
192  * handled those two for us, we additionally deal with missing execute
193  * permission here on some processors
194  */
195 int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
196 			  pte_t *ptep, pte_t entry, int dirty)
197 {
198 	int changed;
199 	entry = set_access_flags_filter(entry, vma, dirty);
200 	changed = !pte_same(*(ptep), entry);
201 	if (changed) {
202 		if (!is_vm_hugetlb_page(vma))
203 			assert_pte_locked(vma->vm_mm, address);
204 		__ptep_set_access_flags(ptep, entry);
205 		flush_tlb_page_nohash(vma, address);
206 	}
207 	return changed;
208 }
209 
210 #ifdef CONFIG_DEBUG_VM
211 void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
212 {
213 	pgd_t *pgd;
214 	pud_t *pud;
215 	pmd_t *pmd;
216 
217 	if (mm == &init_mm)
218 		return;
219 	pgd = mm->pgd + pgd_index(addr);
220 	BUG_ON(pgd_none(*pgd));
221 	pud = pud_offset(pgd, addr);
222 	BUG_ON(pud_none(*pud));
223 	pmd = pmd_offset(pud, addr);
224 	/*
225 	 * khugepaged to collapse normal pages to hugepage, first set
226 	 * pmd to none to force page fault/gup to take mmap_sem. After
227 	 * pmd is set to none, we do a pte_clear which does this assertion
228 	 * so if we find pmd none, return.
229 	 */
230 	if (pmd_none(*pmd))
231 		return;
232 	BUG_ON(!pmd_present(*pmd));
233 	assert_spin_locked(pte_lockptr(mm, pmd));
234 }
235 #endif /* CONFIG_DEBUG_VM */
236 
237