[PATCH 6/6] fuse: convert direct IO paths to use FOLL_PIN

jhubbard.send.patches
2022-02-27T09:34:58Z

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].

[1] https://lore.kernel.org/kvm/20190724061750.GA19397@infradead.org/

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
fs/fuse/dev.c | 7 +++++--
fs/fuse/file.c | 38 +++++++++-----------------------------
2 files changed, 14 insertions(+), 31 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index e1b4a846c90d..9db85c4d549a 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -675,7 +675,10 @@ static void fuse_copy_finish(struct fuse_copy_state *cs)
flush_dcache_page(cs->pg);
set_page_dirty_lock(cs->pg);
}
- put_page(cs->pg);
+ if (cs->pipebufs)
+ put_page(cs->pg);
+ else
+ unpin_user_page(cs->pg);
}
cs->pg = NULL;
}
@@ -730,7 +733,7 @@ static int fuse_copy_fill(struct fuse_copy_state *cs)
}
} else {
size_t off;
- err = iov_iter_get_pages(cs->iter, &page, PAGE_SIZE, 1, &off);
+ err = iov_iter_pin_pages(cs->iter, &page, PAGE_SIZE, 1, &off);
if (err < 0)
return err;
BUG_ON(!err);
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 94747bac3489..ecfa5bdde919 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -611,18 +611,6 @@ void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
args->out_args[0].size = count;
}

-static void fuse_release_user_pages(struct fuse_args_pages *ap,
- bool should_dirty)
-{
- unsigned int i;
-
- for (i = 0; i < ap->num_pages; i++) {
- if (should_dirty)
- set_page_dirty_lock(ap->pages[i]);
- put_page(ap->pages[i]);
- }
-}
-
static void fuse_io_release(struct kref *kref)
{
kfree(container_of(kref, struct fuse_io_priv, refcnt));
@@ -720,7 +708,8 @@ static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
struct fuse_io_priv *io = ia->io;
ssize_t pos = -1;

- fuse_release_user_pages(&ia->ap, io->should_dirty);
+ unpin_user_pages_dirty_lock(ia->ap.pages, ia->ap.num_pages,
+ io->should_dirty);

if (err) {
/* Nothing */
@@ -1382,25 +1371,14 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
size_t nbytes = 0; /* # bytes already packed in req */
ssize_t ret = 0;

- /* Special case for kernel I/O: can copy directly into the buffer */
- if (iov_iter_is_kvec(ii)) {
- unsigned long user_addr = fuse_get_user_addr(ii);
- size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
-
- if (write)
- ap->args.in_args[1].value = (void *) user_addr;
- else
- ap->args.out_args[0].value = (void *) user_addr;
-
- iov_iter_advance(ii, frag_size);
- *nbytesp = frag_size;
- return 0;
- }
+ /* Only user space buffers are allowed with fuse Direct IO. */
+ if (WARN_ON_ONCE(!iter_is_iovec(ii)))
+ return -EOPNOTSUPP;

while (nbytes < *nbytesp && ap->num_pages < max_pages) {
unsigned npages;
size_t start;
- ret = iov_iter_get_pages(ii, &ap->pages[ap->num_pages],
+ ret = iov_iter_pin_pages(ii, &ap->pages[ap->num_pages],
*nbytesp - nbytes,
max_pages - ap->num_pages,
&start);
@@ -1484,7 +1462,9 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
}

if (!io->async || nres < 0) {
- fuse_release_user_pages(&ia->ap, io->should_dirty);
+ unpin_user_pages_dirty_lock(ia->ap.pages,
+ ia->ap.num_pages,
+ io->should_dirty);
fuse_io_free(ia);
}
ia = NULL;
--
2.35.1