diff options
| -rw-r--r-- | include/linux/mm.h | 20 | ||||
| -rw-r--r-- | mm/memory.c | 50 | ||||
| -rw-r--r-- | mm/util.c | 16 |
3 files changed, 67 insertions, 19 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 33da7f53884..a880161a385 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -824,8 +824,11 @@ static inline int handle_mm_fault(struct mm_struct *mm, extern int make_pages_present(unsigned long addr, unsigned long end); extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write); -int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, - int len, int write, int force, struct page **pages, struct vm_area_struct **vmas); +int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, + unsigned long start, int len, int write, int force, + struct page **pages, struct vm_area_struct **vmas); +int get_user_pages_fast(unsigned long start, int nr_pages, int write, + struct page **pages); extern int try_to_release_page(struct page * page, gfp_t gfp_mask); extern void do_invalidatepage(struct page *page, unsigned long offset); @@ -850,19 +853,6 @@ extern int mprotect_fixup(struct vm_area_struct *vma, unsigned long end, unsigned long newflags); /* - * get_user_pages_fast provides equivalent functionality to get_user_pages, - * operating on current and current->mm (force=0 and doesn't return any vmas). - * - * get_user_pages_fast may take mmap_sem and page tables, so no assumptions - * can be made about locking. get_user_pages_fast is to be implemented in a - * way that is advantageous (vs get_user_pages()) when the user memory area is - * already faulted in and present in ptes. However if the pages have to be - * faulted in, it may turn out to be slightly slower). - */ -int get_user_pages_fast(unsigned long start, int nr_pages, int write, - struct page **pages); - -/* * A callback you can register to apply pressure to ageable caches. * * 'shrink' is passed a count 'nr_to_scan' and a 'gfpmask'. It should diff --git a/mm/memory.c b/mm/memory.c index 4126dd16778..891bad0613f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1360,6 +1360,56 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, return i; } +/** + * get_user_pages() - pin user pages in memory + * @tsk: task_struct of target task + * @mm: mm_struct of target mm + * @start: starting user address + * @len: number of pages from start to pin + * @write: whether pages will be written to by the caller + * @force: whether to force write access even if user mapping is + * readonly. This will result in the page being COWed even + * in MAP_SHARED mappings. You do not want this. + * @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 len 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. + */ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, int len, int write, int force, struct page **pages, struct vm_area_struct **vmas) diff --git a/mm/util.c b/mm/util.c index abc65aa7cdf..d5d2213728c 100644 --- a/mm/util.c +++ b/mm/util.c @@ -233,13 +233,21 @@ void arch_pick_mmap_layout(struct mm_struct *mm) * @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. + * + * get_user_pages_fast provides equivalent functionality to get_user_pages, + * operating on current and current->mm, with force=0 and vma=NULL. However + * unlike get_user_pages, it must be called without mmap_sem held. + * + * get_user_pages_fast may take mmap_sem and page table locks, so no + * assumptions can be made about lack of locking. get_user_pages_fast is to be + * implemented in a way that is advantageous (vs get_user_pages()) when the + * user memory area is already faulted in and present in ptes. However if the + * pages have to be faulted in, it may turn out to be slightly slower so + * callers need to carefully consider what to use. On many architectures, + * get_user_pages_fast simply falls back to get_user_pages. */ int __attribute__((weak)) get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) |