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

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

[David Howells]

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@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166722777223.2555743.162508599131141451.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166732024173.3186319.18204305072070871546.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166869687556.3723671.10061142538708346995.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166920902005.1461876.2786264600108839814.stgit@warthog.procyon.org.uk/ # v2
Link: https://lore.kernel.org/r/166997419665.9475.15014699817597102032.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/167305160937.1521586.133299343565358971.stgit@warthog.procyon.org.uk/ # v4
Link: https://lore.kernel.org/r/167344725490.2425628.13771289553670112965.stgit@warthog.procyon.org.uk/ # v5

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

[PATCH v6 17/34] scsi: [RFC] Use netfs_extract_iter_to_sg()

[David Howells]

Use netfs_extract_iter_to_sg() to build a scatterlist from an iterator.

Note that if this fits, netfs_extract_iter_to_sg() should move to core
code.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: James E.J. Bottomley <jejb@linux.ibm.com>
cc: Martin K. Petersen <martin.petersen@oracle.com>
cc: Christoph Hellwig <hch@lst.de>
cc: linux-scsi@vger.kernel.org
---

 drivers/vhost/scsi.c |   78 +++++++++++++++-----------------------------------
 1 file changed, 23 insertions(+), 55 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 5d10837d19ec..af897cc4036d 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -34,6 +34,7 @@
 #include <linux/virtio_scsi.h>
 #include <linux/llist.h>
 #include <linux/bitmap.h>
+#include <linux/netfs.h>
 
 #include "vhost.h"
 
@@ -75,6 +76,9 @@ struct vhost_scsi_cmd {
 	u32 tvc_prot_sgl_count;
 	/* Saved unpacked SCSI LUN for vhost_scsi_target_queue_cmd() */
 	u32 tvc_lun;
+	/* Cleanup modes for scatterlists */
+	unsigned int tvc_cleanup_mode;
+	unsigned int tvc_prot_cleanup_mode;
 	/* Pointer to the SGL formatted memory from virtio-scsi */
 	struct scatterlist *tvc_sgl;
 	struct scatterlist *tvc_prot_sgl;
@@ -339,11 +343,13 @@ static void vhost_scsi_release_cmd_res(struct se_cmd *se_cmd)
 
 	if (tv_cmd->tvc_sgl_count) {
 		for (i = 0; i < tv_cmd->tvc_sgl_count; i++)
-			put_page(sg_page(&tv_cmd->tvc_sgl[i]));
+			page_put_unpin(sg_page(&tv_cmd->tvc_sgl[i]),
+				       tv_cmd->tvc_cleanup_mode);
 	}
 	if (tv_cmd->tvc_prot_sgl_count) {
 		for (i = 0; i < tv_cmd->tvc_prot_sgl_count; i++)
-			put_page(sg_page(&tv_cmd->tvc_prot_sgl[i]));
+			page_put_unpin(sg_page(&tv_cmd->tvc_prot_sgl[i]),
+				       tv_cmd->tvc_prot_cleanup_mode);
 	}
 
 	sbitmap_clear_bit(&svq->scsi_tags, se_cmd->map_tag);
@@ -631,41 +637,6 @@ vhost_scsi_get_cmd(struct vhost_virtqueue *vq, struct vhost_scsi_tpg *tpg,
 	return cmd;
 }
 
-/*
- * Map a user memory range into a scatterlist
- *
- * Returns the number of scatterlist entries used or -errno on error.
- */
-static int
-vhost_scsi_map_to_sgl(struct vhost_scsi_cmd *cmd,
-		      struct iov_iter *iter,
-		      struct scatterlist *sgl,
-		      bool write)
-{
-	struct page **pages = cmd->tvc_upages;
-	struct scatterlist *sg = sgl;
-	ssize_t bytes;
-	size_t offset;
-	unsigned int npages = 0, gup_flags = 0;
-
-	gup_flags |= write ? FOLL_SOURCE_BUF : FOLL_DEST_BUF;
-
-	bytes = iov_iter_get_pages(iter, pages, LONG_MAX,
-				   VHOST_SCSI_PREALLOC_UPAGES, &offset,
-				   gup_flags);
-	/* No pages were pinned */
-	if (bytes <= 0)
-		return bytes < 0 ? bytes : -EFAULT;
-
-	while (bytes) {
-		unsigned n = min_t(unsigned, PAGE_SIZE - offset, bytes);
-		sg_set_page(sg++, pages[npages++], n, offset);
-		bytes -= n;
-		offset = 0;
-	}
-	return npages;
-}
-
 static int
 vhost_scsi_calc_sgls(struct iov_iter *iter, size_t bytes, int max_sgls)
 {
@@ -689,24 +660,19 @@ vhost_scsi_calc_sgls(struct iov_iter *iter, size_t bytes, int max_sgls)
 static int
 vhost_scsi_iov_to_sgl(struct vhost_scsi_cmd *cmd, bool write,
 		      struct iov_iter *iter,
-		      struct scatterlist *sg, int sg_count)
+		      struct scatterlist *sg, int sg_count,
+		      unsigned int *cleanup_mode)
 {
-	struct scatterlist *p = sg;
-	int ret;
+	struct sg_table sgt = { .sgl = sg };
+	unsigned int gup_flags = write ? FOLL_SOURCE_BUF : FOLL_DEST_BUF;
+	ssize_t ret;
 
-	while (iov_iter_count(iter)) {
-		ret = vhost_scsi_map_to_sgl(cmd, iter, sg, write);
-		if (ret < 0) {
-			while (p < sg) {
-				struct page *page = sg_page(p++);
-				if (page)
-					put_page(page);
-			}
-			return ret;
-		}
-		sg += ret;
-	}
-	return 0;
+	ret = netfs_extract_iter_to_sg(iter, LONG_MAX, &sgt, sg_count, gup_flags);
+	if (ret > 0)
+		sg_mark_end(sg + sgt.nents - 1);
+
+	*cleanup_mode = iov_iter_extract_mode(iter, gup_flags);
+	return ret;
 }
 
 static int
@@ -730,7 +696,8 @@ vhost_scsi_mapal(struct vhost_scsi_cmd *cmd,
 
 		ret = vhost_scsi_iov_to_sgl(cmd, write, prot_iter,
 					    cmd->tvc_prot_sgl,
-					    cmd->tvc_prot_sgl_count);
+					    cmd->tvc_prot_sgl_count,
+					    &cmd->tvc_prot_cleanup_mode);
 		if (ret < 0) {
 			cmd->tvc_prot_sgl_count = 0;
 			return ret;
@@ -747,7 +714,8 @@ vhost_scsi_mapal(struct vhost_scsi_cmd *cmd,
 		  cmd->tvc_sgl, cmd->tvc_sgl_count);
 
 	ret = vhost_scsi_iov_to_sgl(cmd, write, data_iter,
-				    cmd->tvc_sgl, cmd->tvc_sgl_count);
+				    cmd->tvc_sgl, cmd->tvc_sgl_count,
+				    &cmd->tvc_cleanup_mode);
 	if (ret < 0) {
 		cmd->tvc_sgl_count = 0;
 		return ret;

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

[Christoph Hellwig]

First off the liver comment:  can we cut down things for a first
round?  Maybe just convert everything using the bio based helpers
and then chunk it up?  Reviewing 34 patches across a dozen subsystems
isn't going to be easy and it will be hard to come up with a final
positive conclusion.