#include <linux/kernel.h> #include <linux/errno.h> #include <linux/err.h> #include <linux/spinlock.h> #include <linux/mm.h> #include <linux/pagemap.h> #include <linux/rmap.h> #include <linux/swap.h> #include <linux/swapops.h> #include <linux/sched.h> #include <linux/rwsem.h> #include <linux/hugetlb.h> #include <asm/pgtable.h> #include <asm/tlbflush.h> #include "internal.h" static struct page *no_page_table(struct vm_area_struct *vma, unsigned int flags) { /* * When core dumping an enormous anonymous area that nobody * has touched so far, we don't want to allocate unnecessary pages or * page tables. Return error instead of NULL to skip handle_mm_fault, * then get_dump_page() will return NULL to leave a hole in the dump. * But we can only make this optimization where a hole would surely * be zero-filled if handle_mm_fault() actually did handle it. */ if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault)) return ERR_PTR(-EFAULT); return NULL; } static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address, pte_t *pte, unsigned int flags) { /* No page to get reference */ if (flags & FOLL_GET) return -EFAULT; if (flags & FOLL_TOUCH) { pte_t entry = *pte; if (flags & FOLL_WRITE) entry = pte_mkdirty(entry); entry = pte_mkyoung(entry); if (!pte_same(*pte, entry)) { set_pte_at(vma->vm_mm, address, pte, entry); update_mmu_cache(vma, address, pte); } } /* Proper page table entry exists, but no corresponding struct page */ return -EEXIST; } static struct page *follow_page_pte(struct vm_area_struct *vma, unsigned long address, pmd_t *pmd, unsigned int flags) { struct mm_struct *mm = vma->vm_mm; struct page *page; spinlock_t *ptl; pte_t *ptep, pte; retry: if (unlikely(pmd_bad(*pmd))) return no_page_table(vma, flags); ptep = pte_offset_map_lock(mm, pmd, address, &ptl); pte = *ptep; if (!pte_present(pte)) { swp_entry_t entry; /* * KSM's break_ksm() relies upon recognizing a ksm page * even while it is being migrated, so for that case we * need migration_entry_wait(). */ if (likely(!(flags & FOLL_MIGRATION))) goto no_page; if (pte_none(pte)) goto no_page; entry = pte_to_swp_entry(pte); if (!is_migration_entry(entry)) goto no_page; pte_unmap_unlock(ptep, ptl); migration_entry_wait(mm, pmd, address); goto retry; } if ((flags & FOLL_NUMA) && pte_protnone(pte)) goto no_page; if ((flags & FOLL_WRITE) && !pte_write(pte)) { pte_unmap_unlock(ptep, ptl); return NULL; } page = vm_normal_page(vma, address, pte); if (unlikely(!page)) { if (flags & FOLL_DUMP) { /* Avoid special (like zero) pages in core dumps */ page = ERR_PTR(-EFAULT); goto out; } if (is_zero_pfn(pte_pfn(pte))) { page = pte_page(pte); } else { int ret; ret = follow_pfn_pte(vma, address, ptep, flags); page = ERR_PTR(ret); goto out; } } if (flags & FOLL_GET) get_page_foll(page); if (flags & FOLL_TOUCH) { if ((flags & FOLL_WRITE) && !pte_dirty(pte) && !PageDirty(page)) set_page_dirty(page); /* * pte_mkyoung() would be more correct here, but atomic care * is needed to avoid losing the dirty bit: it is easier to use * mark_page_accessed(). */ mark_page_accessed(page); } if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) { /* * The preliminary mapping check is mainly to avoid the * pointless overhead of lock_page on the ZERO_PAGE * which might bounce very badly if there is contention. * * If the page is already locked, we don't need to * handle it now - vmscan will handle it later if and * when it attempts to reclaim the page. */ if (page->mapping && trylock_page(page)) { lru_add_drain(); /* push cached pages to LRU */ /* * Because we lock page here, and migration is * blocked by the pte's page reference, and we * know the page is still mapped, we don't even * need to check for file-cache page truncation. */ mlock_vma_page(page); unlock_page(page); } } out: pte_unmap_unlock(ptep, ptl); return page; no_page: pte_unmap_unlock(ptep, ptl); if (!pte_none(pte)) return NULL; return no_page_table(vma, flags); } /** * follow_page_mask - look up a page descriptor from a user-virtual address * @vma: vm_area_struct mapping @address * @address: virtual address to look up * @flags: flags modifying lookup behaviour * @page_mask: on output, *page_mask is set according to the size of the page * * @flags can have FOLL_ flags set, defined in <linux/mm.h> * * Returns the mapped (struct page *), %NULL if no mapping exists, or * an error pointer if there is a mapping to something not represented * by a page descriptor (see also vm_normal_page()). */ struct page *follow_page_mask(struct vm_area_struct *vma, unsigned long address, unsigned int flags, unsigned int *page_mask) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; spinlock_t *ptl; struct page *page; struct mm_struct *mm = vma->vm_mm; *page_mask = 0; page = follow_huge_addr(mm, address, flags & FOLL_WRITE); if (!IS_ERR(page)) { BUG_ON(flags & FOLL_GET); return page; } pgd = pgd_offset(mm, address); if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd))) return no_page_table(vma, flags); pud = pud_offset(pgd, address); if (pud_none(*pud)) return no_page_table(vma, flags); if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) { page = follow_huge_pud(mm, address, pud, flags); if (page) return page; return no_page_table(vma, flags); } if (unlikely(pud_bad(*pud))) return no_page_table(vma, flags); pmd = pmd_offset(pud, address); if (pmd_none(*pmd)) return no_page_table(vma, flags); if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) { page = follow_huge_pmd(mm, address, pmd, flags); if (page) return page; return no_page_table(vma, flags); } if ((flags & FOLL_NUMA) && pmd_protnone(*pmd)) return no_page_table(vma, flags); if (pmd_trans_huge(*pmd)) { if (flags & FOLL_SPLIT) { split_huge_page_pmd(vma, address, pmd); return follow_page_pte(vma, address, pmd, flags); } ptl = pmd_lock(mm, pmd); if (likely(pmd_trans_huge(*pmd))) { if (unlikely(pmd_trans_splitting(*pmd))) { spin_unlock(ptl); wait_split_huge_page(vma->anon_vma, pmd); } else { page = follow_trans_huge_pmd(vma, address, pmd, flags); spin_unlock(ptl); *page_mask = HPAGE_PMD_NR - 1; return page; } } else spin_unlock(ptl); } return follow_page_pte(vma, address, pmd, flags); } static int get_gate_page(struct mm_struct *mm, unsigned long address, unsigned int gup_flags, struct vm_area_struct **vma, struct page **page) { pgd_t *pgd; pud_t *pud; pmd_t *pmd; pte_t *pte; int ret = -EFAULT; /* user gate pages are read-only */ if (gup_flags & FOLL_WRITE) return -EFAULT; if (address > TASK_SIZE) pgd = pgd_offset_k(address); else pgd = pgd_offset_gate(mm, address); BUG_ON(pgd_none(*pgd)); pud = pud_offset(pgd, address); BUG_ON(pud_none(*pud)); pmd = pmd_offset(pud, address); if (pmd_none(*pmd)) return -EFAULT; VM_BUG_ON(pmd_trans_huge(*pmd)); pte = pte_offset_map(pmd, address); if (pte_none(*pte)) goto unmap; *vma = get_gate_vma(mm); if (!page) goto out; *page = vm_normal_page(*vma, address, *pte); if (!*page) { if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte))) goto unmap; *page = pte_page(*pte); } get_page(*page); out: ret = 0; unmap: pte_unmap(pte); return ret; } /* * mmap_sem must be held on entry. If @nonblocking != NULL and * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released. * If it is, *@nonblocking will be set to 0 and -EBUSY returned. */ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma, unsigned long address, unsigned int *flags, int *nonblocking) { struct mm_struct *mm = vma->vm_mm; unsigned int fault_flags = 0; int ret; /* For mm_populate(), just skip the stack guard page. */ if ((*flags & FOLL_POPULATE) && (stack_guard_page_start(vma, address) || stack_guard_page_end(vma, address + PAGE_SIZE))) return -ENOENT; if (*flags & FOLL_WRITE) fault_flags |= FAULT_FLAG_WRITE; if (nonblocking) fault_flags |= FAULT_FLAG_ALLOW_RETRY; if (*flags & FOLL_NOWAIT) fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT; if (*flags & FOLL_TRIED) { VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY); fault_flags |= FAULT_FLAG_TRIED; } ret = handle_mm_fault(mm, vma, address, fault_flags); if (ret & VM_FAULT_ERROR) { if (ret & VM_FAULT_OOM) return -ENOMEM; if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT; if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) return -EFAULT; BUG(); } if (tsk) { if (ret & VM_FAULT_MAJOR) tsk->maj_flt++; else tsk->min_flt++; } if (ret & VM_FAULT_RETRY) { if (nonblocking) *nonblocking = 0; return -EBUSY; } /* * The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when * necessary, even if maybe_mkwrite decided not to set pte_write. We * can thus safely do subsequent page lookups as if they were reads. * But only do so when looping for pte_write is futile: in some cases * userspace may also be wanting to write to the gotten user page, * which a read fault here might prevent (a readonly page might get * reCOWed by userspace write). */ if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE)) *flags &= ~FOLL_WRITE; return 0; } static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags) { vm_flags_t vm_flags = vma->vm_flags; if (vm_flags & (VM_IO | VM_PFNMAP)) return -EFAULT; if (gup_flags & FOLL_WRITE) { if (!(vm_flags & VM_WRITE)) { if (!(gup_flags & FOLL_FORCE)) return -EFAULT; /* * We used to let the write,force case do COW in a * VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could * set a breakpoint in a read-only mapping of an * executable, without corrupting the file (yet only * when that file had been opened for writing!). * Anon pages in shared mappings are surprising: now * just reject it. */ if (!is_cow_mapping(vm_flags)) { WARN_ON_ONCE(vm_flags & VM_MAYWRITE); return -EFAULT; } } } else if (!(vm_flags & VM_READ)) { if (!(gup_flags & FOLL_FORCE)) return -EFAULT; /* * Is there actually any vma we can reach here which does not * have VM_MAYREAD set? */ if (!(vm_flags & VM_MAYREAD)) return -EFAULT; } return 0; } /** * __get_user_pages() - pin user pages in memory * @tsk: task_struct of target task * @mm: mm_struct of target mm * @start: starting user address * @nr_pages: number of pages from start to pin * @gup_flags: flags modifying pin behaviour * @pages: array that receives pointers to the pages pinned. * Should be at least nr_pages long. Or NULL, if caller * only intends to ensure the pages are faulted in. * @vmas: array of pointers to vmas corresponding to each page. * Or NULL if the caller does not require them. * @nonblocking: whether waiting for disk IO or mmap_sem contention * * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. Each page returned must be released * with a put_page() call when it is finished with. vmas will only * remain valid while mmap_sem is held. * * Must be called with mmap_sem held. It may be released. See below. * * __get_user_pages walks a process's page tables and takes a reference to * each struct page that each user address corresponds to at a given * instant. That is, it takes the page that would be accessed if a user * thread accesses the given user virtual address at that instant. * * This does not guarantee that the page exists in the user mappings when * __get_user_pages returns, and there may even be a completely different * page there in some cases (eg. if mmapped pagecache has been invalidated * and subsequently re faulted). However it does guarantee that the page * won't be freed completely. And mostly callers simply care that the page * contains data that was valid *at some point in time*. Typically, an IO * or similar operation cannot guarantee anything stronger anyway because * locks can't be held over the syscall boundary. * * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If * the page is written to, set_page_dirty (or set_page_dirty_lock, as * appropriate) must be called after the page is finished with, and * before put_page is called. * * If @nonblocking != NULL, __get_user_pages will not wait for disk IO * or mmap_sem contention, and if waiting is needed to pin all pages, * *@nonblocking will be set to 0. Further, if @gup_flags does not * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in * this case. * * A caller using such a combination of @nonblocking and @gup_flags * must therefore hold the mmap_sem for reading only, and recognize * when it's been released. Otherwise, it must be held for either * reading or writing and will not be released. * * In most cases, get_user_pages or get_user_pages_fast should be used * instead of __get_user_pages. __get_user_pages should be used only if * you need some special @gup_flags. */ long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas, int *nonblocking) { long i = 0; unsigned int page_mask; struct vm_area_struct *vma = NULL; if (!nr_pages) return 0; VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET)); /* * If FOLL_FORCE is set then do not force a full fault as the hinting * fault information is unrelated to the reference behaviour of a task * using the address space */ if (!(gup_flags & FOLL_FORCE)) gup_flags |= FOLL_NUMA; do { struct page *page; unsigned int foll_flags = gup_flags; unsigned int page_increm; /* first iteration or cross vma bound */ if (!vma || start >= vma->vm_end) { vma = find_extend_vma(mm, start); if (!vma && in_gate_area(mm, start)) { int ret; ret = get_gate_page(mm, start & PAGE_MASK, gup_flags, &vma, pages ? &pages[i] : NULL); if (ret) return i ? : ret; page_mask = 0; goto next_page; } if (!vma || check_vma_flags(vma, gup_flags)) return i ? : -EFAULT; if (is_vm_hugetlb_page(vma)) { i = follow_hugetlb_page(mm, vma, pages, vmas, &start, &nr_pages, i, gup_flags); continue; } } retry: /* * If we have a pending SIGKILL, don't keep faulting pages and * potentially allocating memory. */ if (unlikely(fatal_signal_pending(current))) return i ? i : -ERESTARTSYS; cond_resched(); page = follow_page_mask(vma, start, foll_flags, &page_mask); if (!page) { int ret; ret = faultin_page(tsk, vma, start, &foll_flags, nonblocking); switch (ret) { case 0: goto retry; case -EFAULT: case -ENOMEM: case -EHWPOISON: return i ? i : ret; case -EBUSY: return i; case -ENOENT: goto next_page; } BUG(); } else if (PTR_ERR(page) == -EEXIST) { /* * Proper page table entry exists, but no corresponding * struct page. */ goto next_page; } else if (IS_ERR(page)) { return i ? i : PTR_ERR(page); } if (pages) { pages[i] = page; flush_anon_page(vma, page, start); flush_dcache_page(page); page_mask = 0; } next_page: if (vmas) { vmas[i] = vma; page_mask = 0; } page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask); if (page_increm > nr_pages) page_increm = nr_pages; i += page_increm; start += page_increm * PAGE_SIZE; nr_pages -= page_increm; } while (nr_pages); return i; } EXPORT_SYMBOL(__get_user_pages); /* * fixup_user_fault() - manually resolve a user page fault * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded. * @mm: mm_struct of target mm * @address: user address * @fault_flags:flags to pass down to handle_mm_fault() * * This is meant to be called in the specific scenario where for locking reasons * we try to access user memory in atomic context (within a pagefault_disable() * section), this returns -EFAULT, and we want to resolve the user fault before * trying again. * * Typically this is meant to be used by the futex code. * * The main difference with get_user_pages() is that this function will * unconditionally call handle_mm_fault() which will in turn perform all the * necessary SW fixup of the dirty and young bits in the PTE, while * handle_mm_fault() only guarantees to update these in the struct page. * * This is important for some architectures where those bits also gate the * access permission to the page because they are maintained in software. On * such architectures, gup() will not be enough to make a subsequent access * succeed. * * This has the same semantics wrt the @mm->mmap_sem as does filemap_fault(). */ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, unsigned long address, unsigned int fault_flags) { struct vm_area_struct *vma; vm_flags_t vm_flags; int ret; vma = find_extend_vma(mm, address); if (!vma || address < vma->vm_start) return -EFAULT; vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ; if (!(vm_flags & vma->vm_flags)) return -EFAULT; ret = handle_mm_fault(mm, vma, address, fault_flags); if (ret & VM_FAULT_ERROR) { if (ret & VM_FAULT_OOM) return -ENOMEM; if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE)) return -EHWPOISON; if (ret & (VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV)) return -EFAULT; BUG(); } if (tsk) { if (ret & VM_FAULT_MAJOR) tsk->maj_flt++; else tsk->min_flt++; } return 0; } static __always_inline long __get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, int write, int force, struct page **pages, struct vm_area_struct **vmas, int *locked, bool notify_drop, unsigned int flags) { long ret, pages_done; bool lock_dropped; if (locked) { /* if VM_FAULT_RETRY can be returned, vmas become invalid */ BUG_ON(vmas); /* check caller initialized locked */ BUG_ON(*locked != 1); } if (pages) flags |= FOLL_GET; if (write) flags |= FOLL_WRITE; if (force) flags |= FOLL_FORCE; pages_done = 0; lock_dropped = false; for (;;) { ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas, locked); if (!locked) /* VM_FAULT_RETRY couldn't trigger, bypass */ return ret; /* VM_FAULT_RETRY cannot return errors */ if (!*locked) { BUG_ON(ret < 0); BUG_ON(ret >= nr_pages); } if (!pages) /* If it's a prefault don't insist harder */ return ret; if (ret > 0) { nr_pages -= ret; pages_done += ret; if (!nr_pages) break; } if (*locked) { /* VM_FAULT_RETRY didn't trigger */ if (!pages_done) pages_done = ret; break; } /* VM_FAULT_RETRY triggered, so seek to the faulting offset */ pages += ret; start += ret << PAGE_SHIFT; /* * Repeat on the address that fired VM_FAULT_RETRY * without FAULT_FLAG_ALLOW_RETRY but with * FAULT_FLAG_TRIED. */ *locked = 1; lock_dropped = true; down_read(&mm->mmap_sem); ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED, pages, NULL, NULL); if (ret != 1) { BUG_ON(ret > 1); if (!pages_done) pages_done = ret; break; } nr_pages--; pages_done++; if (!nr_pages) break; pages++; start += PAGE_SIZE; } if (notify_drop && lock_dropped && *locked) { /* * We must let the caller know we temporarily dropped the lock * and so the critical section protected by it was lost. */ up_read(&mm->mmap_sem); *locked = 0; } return pages_done; } /* * We can leverage the VM_FAULT_RETRY functionality in the page fault * paths better by using either get_user_pages_locked() or * get_user_pages_unlocked(). * * get_user_pages_locked() is suitable to replace the form: * * down_read(&mm->mmap_sem); * do_something() * get_user_pages(tsk, mm, ..., pages, NULL); * up_read(&mm->mmap_sem); * * to: * * int locked = 1; * down_read(&mm->mmap_sem); * do_something() * get_user_pages_locked(tsk, mm, ..., pages, &locked); * if (locked) * up_read(&mm->mmap_sem); */ long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, int write, int force, struct page **pages, int *locked) { return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, pages, NULL, locked, true, FOLL_TOUCH); } EXPORT_SYMBOL(get_user_pages_locked); /* * Same as get_user_pages_unlocked(...., FOLL_TOUCH) but it allows to * pass additional gup_flags as last parameter (like FOLL_HWPOISON). * * NOTE: here FOLL_TOUCH is not set implicitly and must be set by the * caller if required (just like with __get_user_pages). "FOLL_GET", * "FOLL_WRITE" and "FOLL_FORCE" are set implicitly as needed * according to the parameters "pages", "write", "force" * respectively. */ __always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, int write, int force, struct page **pages, unsigned int gup_flags) { long ret; int locked = 1; down_read(&mm->mmap_sem); ret = __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, pages, NULL, &locked, false, gup_flags); if (locked) up_read(&mm->mmap_sem); return ret; } EXPORT_SYMBOL(__get_user_pages_unlocked); /* * get_user_pages_unlocked() is suitable to replace the form: * * down_read(&mm->mmap_sem); * get_user_pages(tsk, mm, ..., pages, NULL); * up_read(&mm->mmap_sem); * * with: * * get_user_pages_unlocked(tsk, mm, ..., pages); * * It is functionally equivalent to get_user_pages_fast so * get_user_pages_fast should be used instead, if the two parameters * "tsk" and "mm" are respectively equal to current and current->mm, * or if "force" shall be set to 1 (get_user_pages_fast misses the * "force" parameter). */ long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, int write, int force, struct page **pages) { return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write, force, pages, FOLL_TOUCH); } EXPORT_SYMBOL(get_user_pages_unlocked); /* * get_user_pages() - pin user pages in memory * @tsk: the task_struct to use for page fault accounting, or * NULL if faults are not to be recorded. * @mm: mm_struct of target mm * @start: starting user address * @nr_pages: number of pages from start to pin * @write: whether pages will be written to by the caller * @force: whether to force access even when user mapping is currently * protected (but never forces write access to shared mapping). * @pages: array that receives pointers to the pages pinned. * Should be at least nr_pages long. Or NULL, if caller * only intends to ensure the pages are faulted in. * @vmas: array of pointers to vmas corresponding to each page. * Or NULL if the caller does not require them. * * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. Each page returned must be released * with a put_page() call when it is finished with. vmas will only * remain valid while mmap_sem is held. * * Must be called with mmap_sem held for read or write. * * get_user_pages walks a process's page tables and takes a reference to * each struct page that each user address corresponds to at a given * instant. That is, it takes the page that would be accessed if a user * thread accesses the given user virtual address at that instant. * * This does not guarantee that the page exists in the user mappings when * get_user_pages returns, and there may even be a completely different * page there in some cases (eg. if mmapped pagecache has been invalidated * and subsequently re faulted). However it does guarantee that the page * won't be freed completely. And mostly callers simply care that the page * contains data that was valid *at some point in time*. Typically, an IO * or similar operation cannot guarantee anything stronger anyway because * locks can't be held over the syscall boundary. * * If write=0, the page must not be written to. If the page is written to, * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called * after the page is finished with, and before put_page is called. * * get_user_pages is typically used for fewer-copy IO operations, to get a * handle on the memory by some means other than accesses via the user virtual * addresses. The pages may be submitted for DMA to devices or accessed via * their kernel linear mapping (via the kmap APIs). Care should be taken to * use the correct cache flushing APIs. * * See also get_user_pages_fast, for performance critical applications. * * get_user_pages should be phased out in favor of * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing * should use get_user_pages because it cannot pass * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault. */ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, int write, int force, struct page **pages, struct vm_area_struct **vmas) { return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force, pages, vmas, NULL, false, FOLL_TOUCH); } EXPORT_SYMBOL(get_user_pages); /** * populate_vma_page_range() - populate a range of pages in the vma. * @vma: target vma * @start: start address * @end: end address * @nonblocking: * * This takes care of mlocking the pages too if VM_LOCKED is set. * * return 0 on success, negative error code on error. * * vma->vm_mm->mmap_sem must be held. * * If @nonblocking is NULL, it may be held for read or write and will * be unperturbed. * * If @nonblocking is non-NULL, it must held for read only and may be * released. If it's released, *@nonblocking will be set to 0. */ long populate_vma_page_range(struct vm_area_struct *vma, unsigned long start, unsigned long end, int *nonblocking) { struct mm_struct *mm = vma->vm_mm; unsigned long nr_pages = (end - start) / PAGE_SIZE; int gup_flags; VM_BUG_ON(start & ~PAGE_MASK); VM_BUG_ON(end & ~PAGE_MASK); VM_BUG_ON_VMA(start < vma->vm_start, vma); VM_BUG_ON_VMA(end > vma->vm_end, vma); VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm); gup_flags = FOLL_TOUCH | FOLL_POPULATE; /* * We want to touch writable mappings with a write fault in order * to break COW, except for shared mappings because these don't COW * and we would not want to dirty them for nothing. */ if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE) gup_flags |= FOLL_WRITE; /* * We want mlock to succeed for regions that have any permissions * other than PROT_NONE. */ if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) gup_flags |= FOLL_FORCE; /* * We made sure addr is within a VMA, so the following will * not result in a stack expansion that recurses back here. */ return __get_user_pages(current, mm, start, nr_pages, gup_flags, NULL, NULL, nonblocking); } /* * __mm_populate - populate and/or mlock pages within a range of address space. * * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap * flags. VMAs must be already marked with the desired vm_flags, and * mmap_sem must not be held. */ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors) { struct mm_struct *mm = current->mm; unsigned long end, nstart, nend; struct vm_area_struct *vma = NULL; int locked = 0; long ret = 0; VM_BUG_ON(start & ~PAGE_MASK); VM_BUG_ON(len != PAGE_ALIGN(len)); end = start + len; for (nstart = start; nstart < end; nstart = nend) { /* * We want to fault in pages for [nstart; end) address range. * Find first corresponding VMA. */ if (!locked) { locked = 1; down_read(&mm->mmap_sem); vma = find_vma(mm, nstart); } else if (nstart >= vma->vm_end) vma = vma->vm_next; if (!vma || vma->vm_start >= end) break; /* * Set [nstart; nend) to intersection of desired address * range with the first VMA. Also, skip undesirable VMA types. */ nend = min(end, vma->vm_end); if (vma->vm_flags & (VM_IO | VM_PFNMAP)) continue; if (nstart < vma->vm_start) nstart = vma->vm_start; /* * Now fault in a range of pages. populate_vma_page_range() * double checks the vma flags, so that it won't mlock pages * if the vma was already munlocked. */ ret = populate_vma_page_range(vma, nstart, nend, &locked); if (ret < 0) { if (ignore_errors) { ret = 0; continue; /* continue at next VMA */ } break; } nend = nstart + ret * PAGE_SIZE; ret = 0; } if (locked) up_read(&mm->mmap_sem); return ret; /* 0 or negative error code */ } /** * get_dump_page() - pin user page in memory while writing it to core dump * @addr: user address * * Returns struct page pointer of user page pinned for dump, * to be freed afterwards by page_cache_release() or put_page(). * * Returns NULL on any kind of failure - a hole must then be inserted into * the corefile, to preserve alignment with its headers; and also returns * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found - * allowing a hole to be left in the corefile to save diskspace. * * Called without mmap_sem, but after all other threads have been killed. */ #ifdef CONFIG_ELF_CORE struct page *get_dump_page(unsigned long addr) { struct vm_area_struct *vma; struct page *page; if (__get_user_pages(current, current->mm, addr, 1, FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma, NULL) < 1) return NULL; flush_cache_page(vma, addr, page_to_pfn(page)); return page; } #endif /* CONFIG_ELF_CORE */ /* * Generic RCU Fast GUP * * get_user_pages_fast attempts to pin user pages by walking the page * tables directly and avoids taking locks. Thus the walker needs to be * protected from page table pages being freed from under it, and should * block any THP splits. * * One way to achieve this is to have the walker disable interrupts, and * rely on IPIs from the TLB flushing code blocking before the page table * pages are freed. This is unsuitable for architectures that do not need * to broadcast an IPI when invalidating TLBs. * * Another way to achieve this is to batch up page table containing pages * belonging to more than one mm_user, then rcu_sched a callback to free those * pages. Disabling interrupts will allow the fast_gup walker to both block * the rcu_sched callback, and an IPI that we broadcast for splitting THPs * (which is a relatively rare event). The code below adopts this strategy. * * Before activating this code, please be aware that the following assumptions * are currently made: * * *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free * pages containing page tables. * * *) THP splits will broadcast an IPI, this can be achieved by overriding * pmdp_splitting_flush. * * *) ptes can be read atomically by the architecture. * * *) access_ok is sufficient to validate userspace address ranges. * * The last two assumptions can be relaxed by the addition of helper functions. * * This code is based heavily on the PowerPC implementation by Nick Piggin. */ #ifdef CONFIG_HAVE_GENERIC_RCU_GUP #ifdef __HAVE_ARCH_PTE_SPECIAL static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { pte_t *ptep, *ptem; int ret = 0; ptem = ptep = pte_offset_map(&pmd, addr); do { /* * In the line below we are assuming that the pte can be read * atomically. If this is not the case for your architecture, * please wrap this in a helper function! * * for an example see gup_get_pte in arch/x86/mm/gup.c */ pte_t pte = READ_ONCE(*ptep); struct page *page; /* * Similar to the PMD case below, NUMA hinting must take slow * path using the pte_protnone check. */ if (!pte_present(pte) || pte_special(pte) || pte_protnone(pte) || (write && !pte_write(pte))) goto pte_unmap; VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); if (!page_cache_get_speculative(page)) goto pte_unmap; if (unlikely(pte_val(pte) != pte_val(*ptep))) { put_page(page); goto pte_unmap; } pages[*nr] = page; (*nr)++; } while (ptep++, addr += PAGE_SIZE, addr != end); ret = 1; pte_unmap: pte_unmap(ptem); return ret; } #else /* * If we can't determine whether or not a pte is special, then fail immediately * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not * to be special. * * For a futex to be placed on a THP tail page, get_futex_key requires a * __get_user_pages_fast implementation that can pin pages. Thus it's still * useful to have gup_huge_pmd even if we can't operate on ptes. */ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { return 0; } #endif /* __HAVE_ARCH_PTE_SPECIAL */ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { struct page *head, *page, *tail; int refs; if (write && !pmd_write(orig)) return 0; refs = 0; head = pmd_page(orig); page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT); tail = page; do { VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; refs++; } while (addr += PAGE_SIZE, addr != end); if (!page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) { *nr -= refs; while (refs--) put_page(head); return 0; } /* * Any tail pages need their mapcount reference taken before we * return. (This allows the THP code to bump their ref count when * they are split into base pages). */ while (refs--) { if (PageTail(tail)) get_huge_page_tail(tail); tail++; } return 1; } static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { struct page *head, *page, *tail; int refs; if (write && !pud_write(orig)) return 0; refs = 0; head = pud_page(orig); page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT); tail = page; do { VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; refs++; } while (addr += PAGE_SIZE, addr != end); if (!page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } if (unlikely(pud_val(orig) != pud_val(*pudp))) { *nr -= refs; while (refs--) put_page(head); return 0; } while (refs--) { if (PageTail(tail)) get_huge_page_tail(tail); tail++; } return 1; } static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { int refs; struct page *head, *page, *tail; if (write && !pgd_write(orig)) return 0; refs = 0; head = pgd_page(orig); page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); tail = page; do { VM_BUG_ON_PAGE(compound_head(page) != head, page); pages[*nr] = page; (*nr)++; page++; refs++; } while (addr += PAGE_SIZE, addr != end); if (!page_cache_add_speculative(head, refs)) { *nr -= refs; return 0; } if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) { *nr -= refs; while (refs--) put_page(head); return 0; } while (refs--) { if (PageTail(tail)) get_huge_page_tail(tail); tail++; } return 1; } static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { unsigned long next; pmd_t *pmdp; pmdp = pmd_offset(&pud, addr); do { pmd_t pmd = READ_ONCE(*pmdp); next = pmd_addr_end(addr, end); if (pmd_none(pmd) || pmd_trans_splitting(pmd)) return 0; if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) { /* * NUMA hinting faults need to be handled in the GUP * slowpath for accounting purposes and so that they * can be serialised against THP migration. */ if (pmd_protnone(pmd)) return 0; if (!gup_huge_pmd(pmd, pmdp, addr, next, write, pages, nr)) return 0; } else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) { /* * architecture have different format for hugetlbfs * pmd format and THP pmd format */ if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr, PMD_SHIFT, next, write, pages, nr)) return 0; } else if (!gup_pte_range(pmd, addr, next, write, pages, nr)) return 0; } while (pmdp++, addr = next, addr != end); return 1; } static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, int write, struct page **pages, int *nr) { unsigned long next; pud_t *pudp; pudp = pud_offset(&pgd, addr); do { pud_t pud = READ_ONCE(*pudp); next = pud_addr_end(addr, end); if (pud_none(pud)) return 0; if (unlikely(pud_huge(pud))) { if (!gup_huge_pud(pud, pudp, addr, next, write, pages, nr)) return 0; } else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) { if (!gup_huge_pd(__hugepd(pud_val(pud)), addr, PUD_SHIFT, next, write, pages, nr)) return 0; } else if (!gup_pmd_range(pud, addr, next, write, pages, nr)) return 0; } while (pudp++, addr = next, addr != end); return 1; } /* * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to * the regular GUP. It will only return non-negative values. */ int __get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { struct mm_struct *mm = current->mm; unsigned long addr, len, end; unsigned long next, flags; pgd_t *pgdp; int nr = 0; start &= PAGE_MASK; addr = start; len = (unsigned long) nr_pages << PAGE_SHIFT; end = start + len; if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ, start, len))) return 0; /* * Disable interrupts. We use the nested form as we can already have * interrupts disabled by get_futex_key. * * With interrupts disabled, we block page table pages from being * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h * for more details. * * We do not adopt an rcu_read_lock(.) here as we also want to * block IPIs that come from THPs splitting. */ local_irq_save(flags); pgdp = pgd_offset(mm, addr); do { pgd_t pgd = READ_ONCE(*pgdp); next = pgd_addr_end(addr, end); if (pgd_none(pgd)) break; if (unlikely(pgd_huge(pgd))) { if (!gup_huge_pgd(pgd, pgdp, addr, next, write, pages, &nr)) break; } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) { if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr, PGDIR_SHIFT, next, write, pages, &nr)) break; } else if (!gup_pud_range(pgd, addr, next, write, pages, &nr)) break; } while (pgdp++, addr = next, addr != end); local_irq_restore(flags); return nr; } /** * get_user_pages_fast() - pin user pages in memory * @start: starting user address * @nr_pages: number of pages from start to pin * @write: whether pages will be written to * @pages: array that receives pointers to the pages pinned. * Should be at least nr_pages long. * * Attempt to pin user pages in memory without taking mm->mmap_sem. * If not successful, it will fall back to taking the lock and * calling get_user_pages(). * * Returns number of pages pinned. This may be fewer than the number * requested. If nr_pages is 0 or negative, returns 0. If no pages * were pinned, returns -errno. */ int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { struct mm_struct *mm = current->mm; int nr, ret; start &= PAGE_MASK; nr = __get_user_pages_fast(start, nr_pages, write, pages); ret = nr; if (nr < nr_pages) { /* Try to get the remaining pages with get_user_pages */ start += nr << PAGE_SHIFT; pages += nr; ret = get_user_pages_unlocked(current, mm, start, nr_pages - nr, write, 0, pages); /* Have to be a bit careful with return values */ if (nr > 0) { if (ret < 0) ret = nr; else ret += nr; } } return ret; } #endif /* CONFIG_HAVE_GENERIC_RCU_GUP */