[PATCH 10/17] cifs: Add a function to build an RDMA SGE list from an iterator

David Howells
2023-02-16T21:50:28Z

Add a function to add elements onto an RDMA SGE list representing page
fragments extracted from a BVEC-, KVEC- or XARRAY-type iterator and DMA
mapped until the maximum number of elements is reached.

Nothing is done to make sure the pages remain present - that must be done
by the caller.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Tom Talpey <tom@talpey.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-rdma@vger.kernel.org

Link: https://lore.kernel.org/r/166697256704.61150.17388516338310645808.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/166732028840.3186319.8512284239779728860.stgit@warthog.procyon.org.uk/ # rfc
---
fs/cifs/smbdirect.c | 214 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 214 insertions(+)

diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c
index 8c816b25ce7c..3e0aacddc291 100644
--- a/fs/cifs/smbdirect.c
+++ b/fs/cifs/smbdirect.c
@@ -44,6 +44,17 @@ static int smbd_post_send_page(struct smbd_connection *info,
static void destroy_mr_list(struct smbd_connection *info);
static int allocate_mr_list(struct smbd_connection *info);

+struct smb_extract_to_rdma {
+ struct ib_sge *sge;
+ unsigned int nr_sge;
+ unsigned int max_sge;
+ struct ib_device *device;
+ u32 local_dma_lkey;
+ enum dma_data_direction direction;
+};
+static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
+ struct smb_extract_to_rdma *rdma);
+
/* SMBD version number */
#define SMBD_V1 0x0100

@@ -2490,3 +2501,206 @@ int smbd_deregister_mr(struct smbd_mr *smbdirect_mr)

return rc;
}
+
+static bool smb_set_sge(struct smb_extract_to_rdma *rdma,
+ struct page *lowest_page, size_t off, size_t len)
+{
+ struct ib_sge *sge = &rdma->sge[rdma->nr_sge];
+ u64 addr;
+
+ addr = ib_dma_map_page(rdma->device, lowest_page,
+ off, len, rdma->direction);
+ if (ib_dma_mapping_error(rdma->device, addr))
+ return false;
+
+ sge->addr = addr;
+ sge->length = len;
+ sge->lkey = rdma->local_dma_lkey;
+ rdma->nr_sge++;
+ return true;
+}
+
+/*
+ * Extract page fragments from a BVEC-class iterator and add them to an RDMA
+ * element list. The pages are not pinned.
+ */
+static ssize_t smb_extract_bvec_to_rdma(struct iov_iter *iter,
+ struct smb_extract_to_rdma *rdma,
+ ssize_t maxsize)
+{
+ const struct bio_vec *bv = iter->bvec;
+ unsigned long start = iter->iov_offset;
+ unsigned int i;
+ ssize_t ret = 0;
+
+ for (i = 0; i < iter->nr_segs; i++) {
+ size_t off, len;
+
+ len = bv[i].bv_len;
+ if (start >= len) {
+ start -= len;
+ continue;
+ }
+
+ len = min_t(size_t, maxsize, len - start);
+ off = bv[i].bv_offset + start;
+
+ if (!smb_set_sge(rdma, bv[i].bv_page, off, len))
+ return -EIO;
+
+ ret += len;
+ maxsize -= len;
+ if (rdma->nr_sge >= rdma->max_sge || maxsize <= 0)
+ break;
+ start = 0;
+ }
+
+ return ret;
+}
+
+/*
+ * Extract fragments from a KVEC-class iterator and add them to an RDMA list.
+ * This can deal with vmalloc'd buffers as well as kmalloc'd or static buffers.
+ * The pages are not pinned.
+ */
+static ssize_t smb_extract_kvec_to_rdma(struct iov_iter *iter,
+ struct smb_extract_to_rdma *rdma,
+ ssize_t maxsize)
+{
+ const struct kvec *kv = iter->kvec;
+ unsigned long start = iter->iov_offset;
+ unsigned int i;
+ ssize_t ret = 0;
+
+ for (i = 0; i < iter->nr_segs; i++) {
+ struct page *page;
+ unsigned long kaddr;
+ size_t off, len, seg;
+
+ len = kv[i].iov_len;
+ if (start >= len) {
+ start -= len;
+ continue;
+ }
+
+ kaddr = (unsigned long)kv[i].iov_base + start;
+ off = kaddr & ~PAGE_MASK;
+ len = min_t(size_t, maxsize, len - start);
+ kaddr &= PAGE_MASK;
+
+ maxsize -= len;
+ do {
+ seg = min_t(size_t, len, PAGE_SIZE - off);
+
+ if (is_vmalloc_or_module_addr((void *)kaddr))
+ page = vmalloc_to_page((void *)kaddr);
+ else
+ page = virt_to_page(kaddr);
+
+ if (!smb_set_sge(rdma, page, off, seg))
+ return -EIO;
+
+ ret += seg;
+ len -= seg;
+ kaddr += PAGE_SIZE;
+ off = 0;
+ } while (len > 0 && rdma->nr_sge < rdma->max_sge);
+
+ if (rdma->nr_sge >= rdma->max_sge || maxsize <= 0)
+ break;
+ start = 0;
+ }
+
+ return ret;
+}
+
+/*
+ * Extract folio fragments from an XARRAY-class iterator and add them to an
+ * RDMA list. The folios are not pinned.
+ */
+static ssize_t smb_extract_xarray_to_rdma(struct iov_iter *iter,
+ struct smb_extract_to_rdma *rdma,
+ ssize_t maxsize)
+{
+ struct xarray *xa = iter->xarray;
+ struct folio *folio;
+ loff_t start = iter->xarray_start + iter->iov_offset;
+ pgoff_t index = start / PAGE_SIZE;
+ ssize_t ret = 0;
+ size_t off, len;
+ XA_STATE(xas, xa, index);
+
+ rcu_read_lock();
+
+ xas_for_each(&xas, folio, ULONG_MAX) {
+ if (xas_retry(&xas, folio))
+ continue;
+ if (WARN_ON(xa_is_value(folio)))
+ break;
+ if (WARN_ON(folio_test_hugetlb(folio)))
+ break;
+
+ off = offset_in_folio(folio, start);
+ len = min_t(size_t, maxsize, folio_size(folio) - off);
+
+ if (!smb_set_sge(rdma, folio_page(folio, 0), off, len)) {
+ rcu_read_lock();
+ return -EIO;
+ }
+
+ maxsize -= len;
+ ret += len;
+ if (rdma->nr_sge >= rdma->max_sge || maxsize <= 0)
+ break;
+ }
+
+ rcu_read_unlock();
+ return ret;
+}
+
+/*
+ * Extract page fragments from up to the given amount of the source iterator
+ * and build up an RDMA list that refers to all of those bits. The RDMA list
+ * is appended to, up to the maximum number of elements set in the parameter
+ * block.
+ *
+ * The extracted page fragments are not pinned or ref'd in any way; if an
+ * IOVEC/UBUF-type iterator is to be used, it should be converted to a
+ * BVEC-type iterator and the pages pinned, ref'd or otherwise held in some
+ * way.
+ */
+static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
+ struct smb_extract_to_rdma *rdma)
+{
+ ssize_t ret;
+ int before = rdma->nr_sge;
+
+ switch (iov_iter_type(iter)) {
+ case ITER_BVEC:
+ ret = smb_extract_bvec_to_rdma(iter, rdma, len);
+ break;
+ case ITER_KVEC:
+ ret = smb_extract_kvec_to_rdma(iter, rdma, len);
+ break;
+ case ITER_XARRAY:
+ ret = smb_extract_xarray_to_rdma(iter, rdma, len);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ return -EIO;
+ }
+
+ if (ret > 0) {
+ iov_iter_advance(iter, ret);
+ } else if (ret < 0) {
+ while (rdma->nr_sge > before) {
+ struct ib_sge *sge = &rdma->sge[rdma->nr_sge--];
+
+ ib_dma_unmap_single(rdma->device, sge->addr, sge->length,
+ rdma->direction);
+ sge->addr = 0;
+ }
+ }
+
+ return ret;
+}