iov_iter: add copy_page_to_iter_nofault()

Provide a means to copy a page to user space from an iterator, aborting if
a page fault would occur.  This supports compound pages, but may be passed
a tail page with an offset extending further into the compound page, so we
cannot pass a folio.

This allows for this function to be called from atomic context and _try_
to user pages if they are faulted in, aborting if not.

The function does not use _copy_to_iter() in order to not specify
might_fault(), this is similar to copy_page_from_iter_atomic().

This is being added in order that an iteratable form of vread() can be
implemented while holding spinlocks.

Link: https://lkml.kernel.org/r/19734729defb0f498a76bdec1bef3ac48a3af3e8.1679511146.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Baoquan He <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Liu Shixin <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Uladzislau Rezki (Sony) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions