On 2/28/22 07:59, Miklos Szeredi wrote:

On Sun, 27 Feb 2022 at 10:34, [off-list ref] wrote:

quoted

From: John Hubbard <jhubbard@nvidia.com>

Convert the fuse filesystem to support the new iov_iter_get_pages()
behavior. That routine now invokes pin_user_pages_fast(), which means
that such pages must be released via unpin_user_page(), rather than via
put_page().

This commit also removes any possibility of kernel pages being handled,
in the fuse_get_user_pages() call. Although this may seem like a steep
price to pay, Christoph Hellwig actually recommended it a few years ago
for nearly the same situation [1].

This might work for O_DIRECT, but fuse has this mode of operation
which turns normal "buffered" I/O into direct I/O.  And that in turn
will break execve of such files.

So AFAICS we need to keep kvec handing in some way.

Thanks for bringing that up! Do you have any hints for me, to jump start
a deeper look? And especially, sample programs that exercise this?


thanks,
-- 
John Hubbard
NVIDIA