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Linux/arch/powerpc/mm/pgtable.c

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  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 

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