diff options
| -rw-r--r-- | include/linux/mm.h | 1 | ||||
| -rw-r--r-- | mm/gup.c | 83 |
2 files changed, 43 insertions, 41 deletions
diff --git a/include/linux/mm.h b/include/linux/mm.h index 7e07f4f490cb..e6b884715da1 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2816,6 +2816,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, #define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ #define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ #define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */ +#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */ /* * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each @@ -2731,10 +2731,12 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, struct page **pages) { unsigned long addr, len, end; + unsigned long flags; int nr_pinned = 0, ret = 0; if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | - FOLL_FORCE | FOLL_PIN | FOLL_GET))) + FOLL_FORCE | FOLL_PIN | FOLL_GET | + FOLL_FAST_ONLY))) return -EINVAL; start = untagged_addr(start) & PAGE_MASK; @@ -2753,16 +2755,36 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, * order to avoid confusing the normal COW routines. So only * targets that are already writable are safe to do by just * looking at the page tables. + * + * NOTE! With FOLL_FAST_ONLY we allow read-only gup_fast() here, + * because there is no slow path to fall back on. But you'd + * better be careful about possible COW pages - you'll get _a_ + * COW page, but not necessarily the one you intended to get + * depending on what COW event happens after this. COW may break + * the page copy in a random direction. + * + * Disable interrupts. The nested form is used, in order to allow + * full, general purpose use of this routine. + * + * With interrupts disabled, we block page table pages from being + * freed from under us. See struct mmu_table_batch comments in + * include/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. */ - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && - gup_fast_permitted(start, end)) { - local_irq_disable(); - gup_pgd_range(addr, end, gup_flags | FOLL_WRITE, pages, &nr_pinned); - local_irq_enable(); + if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) { + unsigned long fast_flags = gup_flags; + if (!(gup_flags & FOLL_FAST_ONLY)) + fast_flags |= FOLL_WRITE; + + local_irq_save(flags); + gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned); + local_irq_restore(flags); ret = nr_pinned; } - if (nr_pinned < nr_pages) { + if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) { /* Try to get the remaining pages with get_user_pages */ start += nr_pinned << PAGE_SHIFT; pages += nr_pinned; @@ -2798,51 +2820,30 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, int __get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { - unsigned long len, end; - unsigned long flags; - int nr_pinned = 0; + int nr_pinned; /* * Internally (within mm/gup.c), gup fast variants must set FOLL_GET, * because gup fast is always a "pin with a +1 page refcount" request. + * + * FOLL_FAST_ONLY is required in order to match the API description of + * this routine: no fall back to regular ("slow") GUP. */ - unsigned int gup_flags = FOLL_GET; + unsigned int gup_flags = FOLL_GET | FOLL_FAST_ONLY; if (write) gup_flags |= FOLL_WRITE; - start = untagged_addr(start) & PAGE_MASK; - len = (unsigned long) nr_pages << PAGE_SHIFT; - end = start + len; - - if (end <= start) - return 0; - if (unlikely(!access_ok((void __user *)start, len))) - return 0; + nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags, + pages); /* - * 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 struct mmu_table_batch comments in - * include/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. - * - * NOTE! We allow read-only gup_fast() here, but you'd better be - * careful about possible COW pages. You'll get _a_ COW page, but - * not necessarily the one you intended to get depending on what - * COW event happens after this. COW may break the page copy in a - * random direction. + * As specified in the API description above, this routine is not + * allowed to return negative values. However, the common core + * routine internal_get_user_pages_fast() *can* return -errno. + * Therefore, correct for that here: */ - - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && - gup_fast_permitted(start, end)) { - local_irq_save(flags); - gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); - local_irq_restore(flags); - } + if (nr_pinned < 0) + nr_pinned = 0; return nr_pinned; } |