[PATCH v6 00/34] iov_iter: Improve page extraction (ref, pin or just list)

From: David Howells
Date: Mon Jan 16 2023 - 18:09:00 EST

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Hi Al, Christoph,

Here are patches clean up some use of READ/WRITE and ITER_SOURCE/DEST,
patches to provide support for extracting pages from an iov_iter and a
patch to use the primary extraction function in the block layer bio code.
I've also added a bunch of other conversions and had a tentative stab at
the networking code.

The patches make the following changes:

(1) Deal with switching from using the iterator data_source to indicate
the I/O direction to deriving this from other information, eg.:
IOCB_WRITE, IOMAP_WRITE and the REQ_OP_* number. This allows
iov_iter_rw() to be removed eventually.

(2) Define FOLL_SOURCE_BUF and FOLL_DEST_BUF and pass these into
iov_iter_get_pages*() to indicate the I/O direction with regards to
how the buffer described by the iterator is to be used. This is
included in the gup_flags passed in with Logan's patches.

Calls to iov_iter_get_pages*2() are replaced with calls to
iov_iter_get_pages*() and the former is removed.

(3) Add a function, iov_iter_extract_pages() to replace
iov_iter_get_pages*() that gets refs, pins or just lists the pages as
appropriate to the iterator type and the I/O direction.

Add a function, iov_iter_extract_mode() that will indicate from the
iterator type and the I/O direction how the cleanup is to be
performed, returning FOLL_GET, FOLL_PIN or 0.

Add a function, folio_put_unpin(), and a wrapper, page_put_unpin(),
that take a page and the return from iov_iter_extract_mode() and do
the right thing to clean up the page.

(4) Make the bio struct carry a pair of flags to indicate the cleanup
mode. BIO_NO_PAGE_REF is replaced with BIO_PAGE_REFFED (equivalent to
FOLL_GET) and BIO_PAGE_PINNED (equivalent to BIO_PAGE_PINNED) is
added. These are forced to have the same value as the FOLL_* flags so
they can be passed to the previously mentioned cleanup function.

(5) Make the iter-to-bio code use iov_iter_extract_pages() to
appropriately retain the pages and clean them up later.

(6) Fix bio_flagged() so that it doesn't prevent a gcc optimisation.

(7) Add a function in netfslib, netfs_extract_user_iter(), to extract a
UBUF- or IOVEC-type iterator to a page list in a BVEC-type iterator,
with all the pages suitably ref'd or pinned.

(8) Add a function in netfslib, netfs_extract_iter_to_sg(), to extract a
UBUF-, IOVEC-, BVEC-, XARRAY- or KVEC-type iterator to a scatterlist.
The first two types appropriately ref or pin pages; the latter three
don't perform any retention, leaving that to the caller.

Note that I can make use of this in the SCSI and AF_ALG code and
possibly the networking code, so this might merit being moved to core
code.

(9) Make AF_ALG use iov_iter_extract_pages() and possibly go further and
make it use netfs_extract_iter_to_sg() instead.

(10) Make SCSI vhost use netfs_extract_iter_to_sg().

(11) Make fs/direct-io.c use iov_iter_extract_pages().

(13) Make splice-to-pipe use iov_iter_extract_pages(), but limit the usage
to a cleanup mode of FOLL_GET.

(13) Make the 9P, FUSE and NFS filesystems use iov_iter_extract_pages().

(14) Make the CIFS filesystem use iterators from the top all the way down
to the socket on the simple path. Make it use
netfs_extract_user_iter() to use an XARRAY-type iterator or to build a
BVEC-type iterator in the top layers from a UBUF- or IOVEC-type
iterator and attach the iterator to the operation descriptors.

netfs_extract_iter_to_sg() is used to build scatterlists for doing
transport crypto and a function, smb_extract_iter_to_rdma(), is
provided to build an RDMA SGE list directly from an iterator without
going via a page list and then a scatter list.

(15) A couple of work-in-progress patches to try and make sk_buff fragments
record the information needed to clean them up in the lowest two bits
of the page pointer in the fragment struct.

This leaves:

(*) Four calls to iov_iter_get_pages() in CEPH. That will be helped by
patches to pass an iterator down to the transport layer instead of
converting to a page list high up and passing that down, but the
transport layer could do with some massaging so that it doesn't covert
the iterator to a page list and then the pages individually back to
iterators to pass to the socket.

(*) One call to iov_iter_get_pages() each in the networking core, RDS and
TLS, all related to zero-copy. TLS seems to do zerocopy-read (or
maybe decrypt-offload) and should be doing FOLL_PIN, not FOLL_GET for
user-provided buffers.

Changes:
========
ver #6)
- Fix write() syscall and co. not setting IOCB_WRITE.
- Added iocb_is_read() and iocb_is_write() to check IOCB_WRITE.
- Use op_is_write() in bio_copy_user_iov().
- Drop the iterator direction checks from smbd_recv().
- Define FOLL_SOURCE_BUF and FOLL_DEST_BUF and pass them in as part of
gup_flags to iov_iter_get/extract_pages*().
- Replace iov_iter_get_pages*2() with iov_iter_get_pages*() and remove.
- Add back the function to indicate the cleanup mode.
- Drop the cleanup_mode return arg to iov_iter_extract_pages().
- Provide a helper to clean up a page.
- Renumbered FOLL_GET and FOLL_PIN and made BIO_PAGE_REFFED/PINNED have
the same numerical values, enforced with an assertion.
- Converted AF_ALG, SCSI vhost, generic DIO, FUSE, splice to pipe, 9P and
NFS.
- Added in the patches to make CIFS do top-to-bottom iterators and use
various of the added extraction functions.
- Added a pair of work-in-progess patches to make sk_buff fragments store
FOLL_GET and FOLL_PIN.

ver #5)
- Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED and split into own patch.
- Transcribe FOLL_GET/PIN into BIO_PAGE_REFFED/PINNED flags.
- Add patch to allow bio_flagged() to be combined by gcc.

ver #4)
- Drop the patch to move the FOLL_* flags to linux/mm_types.h as they're
no longer referenced by linux/uio.h.
- Add ITER_SOURCE/DEST cleanup patches.
- Make iov_iter/netfslib iter extraction patches use ITER_SOURCE/DEST.
- Allow additional gup_flags to be passed into iov_iter_extract_pages().
- Add struct bio patch.

ver #3)
- Switch to using EXPORT_SYMBOL_GPL to prevent indirect 3rd-party access
to get/pin_user_pages_fast()[1].

ver #2)
- Rolled the extraction cleanup mode query function into the extraction
function, returning the indication through the argument list.
- Fixed patch 4 (extract to scatterlist) to actually use the new
extraction API.

I've pushed the patches (excluding the two WIP networking patches) here
also:

https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-extract

David

Link: https://lore.kernel.org/r/Y3zFzdWnWlEJ8X8/@infradead.org/ [1]
Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166920902005.1461876.2786264600108839814.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2
Link: https://lore.kernel.org/r/166997419665.9475.15014699817597102032.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3
Link: https://lore.kernel.org/r/167305160937.1521586.133299343565358971.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v4
Link: https://lore.kernel.org/r/167344725490.2425628.13771289553670112965.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v5

Previous versions of the CIFS patch sets can be found here:
Link: https://lore.kernel.org/r/164311902471.2806745.10187041199819525677.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/164928615045.457102.10607899252434268982.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/165211416682.3154751.17287804906832979514.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/165348876794.2106726.9240233279581920208.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/165364823513.3334034.11209090728654641458.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v3
Link: https://lore.kernel.org/r/166126392703.708021.14465850073772688008.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1
Link: https://lore.kernel.org/r/166697254399.61150.1256557652599252121.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # rfc

---
David Howells (34):
vfs: Unconditionally set IOCB_WRITE in call_write_iter()
iov_iter: Use IOCB/IOMAP_WRITE/op_is_write rather than iterator direction
iov_iter: Pass I/O direction into iov_iter_get_pages*()
iov_iter: Remove iov_iter_get_pages2/pages_alloc2()
iov_iter: Change the direction macros into an enum
iov_iter: Use the direction in the iterator functions
iov_iter: Add a function to extract a page list from an iterator
mm: Provide a helper to drop a pin/ref on a page
bio: Rename BIO_NO_PAGE_REF to BIO_PAGE_REFFED and invert the meaning
mm, block: Make BIO_PAGE_REFFED/PINNED the same as FOLL_GET/PIN numerically
iov_iter, block: Make bio structs pin pages rather than ref'ing if appropriate
bio: Fix bio_flagged() so that gcc can better optimise it
netfs: Add a function to extract a UBUF or IOVEC into a BVEC iterator
netfs: Add a function to extract an iterator into a scatterlist
af_alg: Pin pages rather than ref'ing if appropriate
af_alg: [RFC] Use netfs_extract_iter_to_sg() to create scatterlists
scsi: [RFC] Use netfs_extract_iter_to_sg()
dio: Pin pages rather than ref'ing if appropriate
fuse: Pin pages rather than ref'ing if appropriate
vfs: Make splice use iov_iter_extract_pages()
9p: Pin pages rather than ref'ing if appropriate
nfs: Pin pages rather than ref'ing if appropriate
cifs: Implement splice_read to pass down ITER_BVEC not ITER_PIPE
cifs: Add a function to build an RDMA SGE list from an iterator
cifs: Add a function to Hash the contents of an iterator
cifs: Add some helper functions
cifs: Add a function to read into an iter from a socket
cifs: Change the I/O paths to use an iterator rather than a page list
cifs: Build the RDMA SGE list directly from an iterator
cifs: Remove unused code
cifs: Fix problem with encrypted RDMA data read
cifs: DIO to/from KVEC-type iterators should now work
net: [RFC][WIP] Mark each skb_frags as to how they should be cleaned up
net: [RFC][WIP] Make __zerocopy_sg_from_iter() correctly pin or leave pages unref'd

block/bio.c | 48 +-
block/blk-map.c | 26 +-
block/blk.h | 25 +
block/fops.c | 8 +-
crypto/af_alg.c | 57 +-
crypto/algif_hash.c | 20 +-
drivers/net/tun.c | 2 +-
drivers/vhost/scsi.c | 75 +-
fs/9p/vfs_addr.c | 2 +-
fs/affs/file.c | 4 +-
fs/ceph/addr.c | 2 +-
fs/ceph/file.c | 16 +-
fs/cifs/Kconfig | 1 +
fs/cifs/cifsencrypt.c | 172 +++-
fs/cifs/cifsfs.c | 12 +-
fs/cifs/cifsfs.h | 6 +
fs/cifs/cifsglob.h | 66 +-
fs/cifs/cifsproto.h | 11 +-
fs/cifs/cifssmb.c | 13 +-
fs/cifs/connect.c | 16 +
fs/cifs/file.c | 1851 +++++++++++++++++--------------------
fs/cifs/fscache.c | 22 +-
fs/cifs/fscache.h | 10 +-
fs/cifs/misc.c | 132 +--
fs/cifs/smb2ops.c | 374 ++++----
fs/cifs/smb2pdu.c | 45 +-
fs/cifs/smbdirect.c | 511 ++++++----
fs/cifs/smbdirect.h | 4 +-
fs/cifs/transport.c | 57 +-
fs/dax.c | 6 +-
fs/direct-io.c | 77 +-
fs/exfat/inode.c | 6 +-
fs/ext2/inode.c | 2 +-
fs/f2fs/file.c | 10 +-
fs/fat/inode.c | 4 +-
fs/fuse/dax.c | 2 +-
fs/fuse/dev.c | 24 +-
fs/fuse/file.c | 34 +-
fs/fuse/fuse_i.h | 1 +
fs/hfs/inode.c | 2 +-
fs/hfsplus/inode.c | 2 +-
fs/iomap/direct-io.c | 6 +-
fs/jfs/inode.c | 2 +-
fs/netfs/Makefile | 1 +
fs/netfs/iterator.c | 371 ++++++++
fs/nfs/direct.c | 32 +-
fs/nilfs2/inode.c | 2 +-
fs/ntfs3/inode.c | 2 +-
fs/ocfs2/aops.c | 2 +-
fs/orangefs/inode.c | 2 +-
fs/reiserfs/inode.c | 2 +-
fs/splice.c | 10 +-
fs/udf/inode.c | 2 +-
include/crypto/if_alg.h | 7 +-
include/linux/bio.h | 23 +-
include/linux/blk_types.h | 3 +-
include/linux/fs.h | 11 +
include/linux/mm.h | 32 +-
include/linux/netfs.h | 6 +
include/linux/skbuff.h | 124 ++-
include/linux/uio.h | 83 +-
io_uring/net.c | 2 +-
lib/iov_iter.c | 428 ++++++++-
mm/gup.c | 47 +
mm/vmalloc.c | 1 +
net/9p/trans_common.c | 6 +-
net/9p/trans_common.h | 3 +-
net/9p/trans_virtio.c | 91 +-
net/bpf/test_run.c | 2 +-
net/core/datagram.c | 23 +-
net/core/gro.c | 2 +-
net/core/skbuff.c | 16 +-
net/core/skmsg.c | 4 +-
net/ipv4/ip_output.c | 2 +-
net/ipv4/tcp.c | 4 +-
net/ipv6/esp6.c | 5 +-
net/ipv6/ip6_output.c | 2 +-
net/packet/af_packet.c | 2 +-
net/rds/message.c | 4 +-
net/tls/tls_sw.c | 5 +-
net/xfrm/xfrm_ipcomp.c | 2 +-
81 files changed, 3006 insertions(+), 2126 deletions(-)
create mode 100644 fs/netfs/iterator.c

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