diff options
Diffstat (limited to 'include/linux/mm.h')
| -rw-r--r-- | include/linux/mm.h | 41 |
1 files changed, 28 insertions, 13 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 083d7b4863ed..8bc677ce8f01 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1505,19 +1505,6 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages, long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, struct page **pages, unsigned int gup_flags); -#if defined(CONFIG_FS_DAX) || defined(CONFIG_CMA) -long get_user_pages_longterm(unsigned long start, unsigned long nr_pages, - unsigned int gup_flags, struct page **pages, - struct vm_area_struct **vmas); -#else -static inline long get_user_pages_longterm(unsigned long start, - unsigned long nr_pages, unsigned int gup_flags, - struct page **pages, struct vm_area_struct **vmas) -{ - return get_user_pages(start, nr_pages, gup_flags, pages, vmas); -} -#endif /* CONFIG_FS_DAX */ - int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages); @@ -2583,6 +2570,34 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, #define FOLL_REMOTE 0x2000 /* we are working on non-current tsk/mm */ #define FOLL_COW 0x4000 /* internal GUP flag */ #define FOLL_ANON 0x8000 /* don't do file mappings */ +#define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ + +/* + * NOTE on FOLL_LONGTERM: + * + * FOLL_LONGTERM indicates that the page will be held for an indefinite time + * period _often_ under userspace control. This is contrasted with + * iov_iter_get_pages() where usages which are transient. + * + * FIXME: For pages which are part of a filesystem, mappings are subject to the + * lifetime enforced by the filesystem and we need guarantees that longterm + * users like RDMA and V4L2 only establish mappings which coordinate usage with + * the filesystem. Ideas for this coordination include revoking the longterm + * pin, delaying writeback, bounce buffer page writeback, etc. As FS DAX was + * added after the problem with filesystems was found FS DAX VMAs are + * specifically failed. Filesystem pages are still subject to bugs and use of + * FOLL_LONGTERM should be avoided on those pages. + * + * FIXME: Also NOTE that FOLL_LONGTERM is not supported in every GUP call. + * Currently only get_user_pages() and get_user_pages_fast() support this flag + * and calls to get_user_pages_[un]locked are specifically not allowed. This + * is due to an incompatibility with the FS DAX check and + * FAULT_FLAG_ALLOW_RETRY + * + * In the CMA case: longterm pins in a CMA region would unnecessarily fragment + * that region. And so CMA attempts to migrate the page before pinning when + * FOLL_LONGTERM is specified. + */ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) { |