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author | Andreas Gruenbacher <agruenba@redhat.com> | 2021-07-05 17:26:28 +0200 |
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committer | Andreas Gruenbacher <agruenba@redhat.com> | 2021-10-20 19:33:07 +0200 |
commit | cdd591fc86e38ad3899196066219fbbd845f3162 (patch) | |
tree | 6fa9b67d1df07be3b57ba43a66120c0c4fd63450 /mm/gup.c | |
parent | iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable (diff) | |
download | linux-cdd591fc86e38ad3899196066219fbbd845f3162.tar.xz linux-cdd591fc86e38ad3899196066219fbbd845f3162.zip |
iov_iter: Introduce fault_in_iov_iter_writeable
Introduce a new fault_in_iov_iter_writeable helper for safely faulting
in an iterator for writing. Uses get_user_pages() to fault in the pages
without actually writing to them, which would be destructive.
We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that
the iterator passed to .read_iter isn't in memory.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Diffstat (limited to 'mm/gup.c')
-rw-r--r-- | mm/gup.c | 63 |
1 files changed, 63 insertions, 0 deletions
@@ -1691,6 +1691,69 @@ out: } EXPORT_SYMBOL(fault_in_writeable); +/* + * fault_in_safe_writeable - fault in an address range for writing + * @uaddr: start of address range + * @size: length of address range + * + * Faults in an address range using get_user_pages, i.e., without triggering + * hardware page faults. This is primarily useful when we already know that + * some or all of the pages in the address range aren't in memory. + * + * Other than fault_in_writeable(), this function is non-destructive. + * + * Note that we don't pin or otherwise hold the pages referenced that we fault + * in. There's no guarantee that they'll stay in memory for any duration of + * time. + * + * Returns the number of bytes not faulted in, like copy_to_user() and + * copy_from_user(). + */ +size_t fault_in_safe_writeable(const char __user *uaddr, size_t size) +{ + unsigned long start = (unsigned long)untagged_addr(uaddr); + unsigned long end, nstart, nend; + struct mm_struct *mm = current->mm; + struct vm_area_struct *vma = NULL; + int locked = 0; + + nstart = start & PAGE_MASK; + end = PAGE_ALIGN(start + size); + if (end < nstart) + end = 0; + for (; nstart != end; nstart = nend) { + unsigned long nr_pages; + long ret; + + if (!locked) { + locked = 1; + mmap_read_lock(mm); + vma = find_vma(mm, nstart); + } else if (nstart >= vma->vm_end) + vma = vma->vm_next; + if (!vma || vma->vm_start >= end) + break; + nend = end ? min(end, vma->vm_end) : vma->vm_end; + if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + continue; + if (nstart < vma->vm_start) + nstart = vma->vm_start; + nr_pages = (nend - nstart) / PAGE_SIZE; + ret = __get_user_pages_locked(mm, nstart, nr_pages, + NULL, NULL, &locked, + FOLL_TOUCH | FOLL_WRITE); + if (ret <= 0) + break; + nend = nstart + ret * PAGE_SIZE; + } + if (locked) + mmap_read_unlock(mm); + if (nstart == end) + return 0; + return size - min_t(size_t, nstart - start, size); +} +EXPORT_SYMBOL(fault_in_safe_writeable); + /** * fault_in_readable - fault in userspace address range for reading * @uaddr: start of user address range |