Message-Id: <20190806123154.23798-3-suwan.kim027@gmail.com>
Date:   Tue,  6 Aug 2019 21:31:54 +0900
From:   Suwan Kim <suwan.kim027@...il.com>
To:     shuah@...nel.org, valentina.manea.m@...il.com,
        gregkh@...uxfoundation.org, stern@...land.harvard.edu
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Suwan Kim <suwan.kim027@...il.com>
Subject: [PATCH v4 2/2] usbip: Implement SG support to vhci-hcd and stub driver

There are bugs on vhci with usb 3.0 storage device. In USB, each SG
list entry buffer should be divisible by the bulk max packet size.
But with native SG support, this problem doesn't matter because the
SG buffer is treated as contiguous buffer. But without native SG
support, USB storage driver breaks SG list into several URBs and the
error occurs because of a buffer size of URB that cannot be divided
by the bulk max packet size. The error situation is as follows.

When USB Storage driver requests 31.5 KB data and has SG list which
has 3584 bytes buffer followed by 7 4096 bytes buffer for some
reason. USB Storage driver splits this SG list into several URBs
because VHCI doesn't support SG and sends them separately. So the
first URB buffer size is 3584 bytes. When receiving data from device,
USB 3.0 device sends data packet of 1024 bytes size because the max
packet size of BULK pipe is 1024 bytes. So device sends 4096 bytes.
But the first URB buffer has only 3584 bytes buffer size. So host
controller terminates the transfer even though there is more data to
receive. So, vhci needs to support SG transfer to prevent this error.

In this patch, vhci supports SG regardless of whether the server's
host controller supports SG or not, because stub driver splits SG
list into several URBs if the server's host controller doesn't
support SG.

To support SG, vhci_map_urb_for_dma() sets URB_DMA_MAP_SG flag in
urb->transfer_flags if URB has SG list and this flag will tell stub
driver to use SG list.

vhci sends each SG list entry to stub driver. Then, stub driver sees
the total length of the buffer and allocates SG table and pages
according to the total buffer length calling sgl_alloc(). After stub
driver receives completed URB, it again sends each SG list entry to
vhci.

If the server's host controller doesn't support SG, stub driver
breaks a single SG request into several URBs and submits them to
the server's host controller. When all the split URBs are completed,
stub driver reassembles the URBs into a single return command and
sends it to vhci.

Moreover, in the situation where vhci supports SG, but stub driver
does not, or vice versa, usbip works normally. Because there is no
protocol modification, there is no problem in communication between
server and client even if the one has a kernel without SG support.

In the case of vhci supports SG and stub driver doesn't, because
vhci sends only the total length of the buffer to stub driver as
it did before the patch applied, stub driver only needs to allocate
the required length of buffers regardless of whether vhci supports
SG or not.

If stub driver needs to send data buffer to vhci because of IN pipe,
stub driver also sends only total length of buffer as metadata and
then sends real data as vhci does. Then vhci receive data from stub
driver and store it to the corresponding buffer of SG list entry.

In the case of stub driver that supports SG, buffer is allocated by
sgl_alloc(). However, stub driver that does not support SG allocates
buffer using only kmalloc(). Therefore, if vhci supports SG and stub
driver doesn't, stub driver has to allocate buffer with kmalloc() as
much as the total length of SG buffer which is quite huge when vhci
sends SG request, so it has big overhead in buffer allocation.

And for the case of stub driver supports SG and vhci doesn't, since
the USB storage driver checks that vhci doesn't support SG and sends
the request to stub driver by splitting the SG list into multiple
URBs, stub driver allocates a buffer with kmalloc() as it did before
this patch.

VUDC also works well with this patch. Tests are done with two USB
gadget created by CONFIGFS USB gadget. Both use the BULK pipe.

        1. Serial gadget
        2. Mass storage gadget

 * Serial gadget test

Serial gadget on the host sends and receives data using cat command
on the /dev/ttyGS<N>. The client uses minicom to communicate with
the serial gadget.

 * Mass storage gadget test

After connecting the gadget with vhci, use "dd" to test read and
write operation on the client side.

Read  - dd if=/dev/sd<N> iflag=direct of=/dev/null bs=1G count=1
Write - dd if=<my file path> iflag=direct of=/dev/sd<N> bs=1G count=1

Signed-off-by: Suwan Kim <suwan.kim027@...il.com>
---
v3 - v4

- Rewrite the description about the vhci bug with USB 3.0 storage
  device.
- Add the description about the test with VUDC.
- Fix the error message in stub_recv_cmd_unlink().

v2 - v3

- Rewrite the commit log to make it more clear.
- Add the description about the mismatch situation in commit log.
- Run chechpatch.pl and fix errors with coding style and typos.
- Fix the error path of usbip_recv_xbuff() to stop receiving data
  after TCP error occurs.
- Consolidate the duplicated error path in usbip_recv_xbuff() and
  vhci_send_cmd_submit().
- Undo the unnecessary changes
  * Undo the deletion of empty line in stub_send_ret_submit()
  * Move memset() lines in stub_send_ret_submit() to the original
    position.

v1 - v2

- Add the logic that splits single SG request into several URBs in
  stub driver if server’s HC doesn’t support SG.
---
 drivers/usb/usbip/stub.h         |   7 +-
 drivers/usb/usbip/stub_main.c    |  55 ++++++---
 drivers/usb/usbip/stub_rx.c      | 204 ++++++++++++++++++++++---------
 drivers/usb/usbip/stub_tx.c      |  99 +++++++++++----
 drivers/usb/usbip/usbip_common.c |  59 ++++++---
 drivers/usb/usbip/vhci_hcd.c     |  15 ++-
 drivers/usb/usbip/vhci_tx.c      |  63 ++++++++--
 7 files changed, 376 insertions(+), 126 deletions(-)

diff --git a/drivers/usb/usbip/stub.h b/drivers/usb/usbip/stub.h
index 35618ceb2791..d11270560c24 100644
--- a/drivers/usb/usbip/stub.h
+++ b/drivers/usb/usbip/stub.h
@@ -52,7 +52,11 @@ struct stub_priv {
 	unsigned long seqnum;
 	struct list_head list;
 	struct stub_device *sdev;
-	struct urb *urb;
+	struct urb **urbs;
+	struct scatterlist *sgl;
+	int num_urbs;
+	int completed_urbs;
+	int urb_status;
 
 	int unlinking;
 };
@@ -86,6 +90,7 @@ extern struct usb_device_driver stub_driver;
 struct bus_id_priv *get_busid_priv(const char *busid);
 void put_busid_priv(struct bus_id_priv *bid);
 int del_match_busid(char *busid);
+void stub_free_priv_and_urb(struct stub_priv *priv);
 void stub_device_cleanup_urbs(struct stub_device *sdev);
 
 /* stub_rx.c */
diff --git a/drivers/usb/usbip/stub_main.c b/drivers/usb/usbip/stub_main.c
index 2e4bfccd4bfc..3ee636215e9c 100644
--- a/drivers/usb/usbip/stub_main.c
+++ b/drivers/usb/usbip/stub_main.c
@@ -6,6 +6,7 @@
 #include <linux/string.h>
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
@@ -288,6 +289,42 @@ static struct stub_priv *stub_priv_pop_from_listhead(struct list_head *listhead)
 	return NULL;
 }
 
+void stub_free_priv_and_urb(struct stub_priv *priv)
+{
+	struct urb *urb;
+	int i;
+
+	for (i = 0; i < priv->num_urbs; i++) {
+		urb = priv->urbs[i];
+
+		if (!urb)
+			return;
+
+		kfree(urb->setup_packet);
+		urb->setup_packet = NULL;
+
+
+		if (urb->transfer_buffer && !priv->sgl) {
+			kfree(urb->transfer_buffer);
+			urb->transfer_buffer = NULL;
+		}
+
+		if (urb->num_sgs) {
+			sgl_free(urb->sg);
+			urb->sg = NULL;
+			urb->num_sgs = 0;
+		}
+
+		usb_free_urb(urb);
+	}
+
+	list_del(&priv->list);
+	if (priv->sgl)
+		sgl_free(priv->sgl);
+	kfree(priv->urbs);
+	kmem_cache_free(stub_priv_cache, priv);
+}
+
 static struct stub_priv *stub_priv_pop(struct stub_device *sdev)
 {
 	unsigned long flags;
@@ -314,25 +351,15 @@ static struct stub_priv *stub_priv_pop(struct stub_device *sdev)
 void stub_device_cleanup_urbs(struct stub_device *sdev)
 {
 	struct stub_priv *priv;
-	struct urb *urb;
+	int i;
 
 	dev_dbg(&sdev->udev->dev, "Stub device cleaning up urbs\n");
 
 	while ((priv = stub_priv_pop(sdev))) {
-		urb = priv->urb;
-		dev_dbg(&sdev->udev->dev, "free urb seqnum %lu\n",
-			priv->seqnum);
-		usb_kill_urb(urb);
+		for (i = 0; i < priv->num_urbs; i++)
+			usb_kill_urb(priv->urbs[i]);
 
-		kmem_cache_free(stub_priv_cache, priv);
-
-		kfree(urb->transfer_buffer);
-		urb->transfer_buffer = NULL;
-
-		kfree(urb->setup_packet);
-		urb->setup_packet = NULL;
-
-		usb_free_urb(urb);
+		stub_free_priv_and_urb(priv);
 	}
 }
 
diff --git a/drivers/usb/usbip/stub_rx.c b/drivers/usb/usbip/stub_rx.c
index b0a855acafa3..66edfeea68fe 100644
--- a/drivers/usb/usbip/stub_rx.c
+++ b/drivers/usb/usbip/stub_rx.c
@@ -7,6 +7,7 @@
 #include <linux/kthread.h>
 #include <linux/usb.h>
 #include <linux/usb/hcd.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
@@ -201,7 +202,7 @@ static void tweak_special_requests(struct urb *urb)
 static int stub_recv_cmd_unlink(struct stub_device *sdev,
 				struct usbip_header *pdu)
 {
-	int ret;
+	int ret, i;
 	unsigned long flags;
 	struct stub_priv *priv;
 
@@ -246,12 +247,14 @@ static int stub_recv_cmd_unlink(struct stub_device *sdev,
 		 * so a driver in a client host will know the failure
 		 * of the unlink request ?
 		 */
-		ret = usb_unlink_urb(priv->urb);
-		if (ret != -EINPROGRESS)
-			dev_err(&priv->urb->dev->dev,
-				"failed to unlink a urb # %lu, ret %d\n",
-				priv->seqnum, ret);
-
+		for (i = priv->completed_urbs; i < priv->num_urbs; i++) {
+			ret = usb_unlink_urb(priv->urbs[i]);
+			if (ret != -EINPROGRESS)
+				dev_err(&priv->urbs[i]->dev->dev,
+					"failed to unlink %d/%d urb of seqnum %lu, ret %d\n",
+					i + 1, priv->num_urbs,
+					priv->seqnum, ret);
+		}
 		return 0;
 	}
 
@@ -433,14 +436,36 @@ static void masking_bogus_flags(struct urb *urb)
 	urb->transfer_flags &= allowed;
 }
 
+static int stub_recv_xbuff(struct usbip_device *ud, struct stub_priv *priv)
+{
+	int ret;
+	int i;
+
+	for (i = 0; i < priv->num_urbs; i++) {
+		ret = usbip_recv_xbuff(ud, priv->urbs[i]);
+		if (ret < 0)
+			break;
+	}
+
+	return ret;
+}
+
 static void stub_recv_cmd_submit(struct stub_device *sdev,
 				 struct usbip_header *pdu)
 {
-	int ret;
 	struct stub_priv *priv;
 	struct usbip_device *ud = &sdev->ud;
 	struct usb_device *udev = sdev->udev;
+	struct scatterlist *sgl = NULL, *sg;
+	void *buffer = NULL;
+	unsigned long long buf_len;
+	int nents;
+	int num_urbs = 1;
 	int pipe = get_pipe(sdev, pdu);
+	int use_sg = pdu->u.cmd_submit.transfer_flags & URB_DMA_MAP_SG;
+	int support_sg = 1;
+	int np = 0;
+	int ret, i;
 
 	if (pipe == -1)
 		return;
@@ -449,76 +474,139 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
 	if (!priv)
 		return;
 
-	/* setup a urb */
-	if (usb_pipeisoc(pipe))
-		priv->urb = usb_alloc_urb(pdu->u.cmd_submit.number_of_packets,
-					  GFP_KERNEL);
-	else
-		priv->urb = usb_alloc_urb(0, GFP_KERNEL);
+	buf_len = (unsigned long long)pdu->u.cmd_submit.transfer_buffer_length;
 
-	if (!priv->urb) {
-		usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
-		return;
+	/* allocate urb transfer buffer, if needed */
+	if (buf_len) {
+		if (use_sg) {
+			sgl = sgl_alloc(buf_len, GFP_KERNEL, &nents);
+			if (!sgl)
+				goto err_malloc;
+		} else {
+			buffer = kzalloc(buf_len, GFP_KERNEL);
+			if (!buffer)
+				goto err_malloc;
+		}
 	}
 
-	/* allocate urb transfer buffer, if needed */
-	if (pdu->u.cmd_submit.transfer_buffer_length > 0) {
-		priv->urb->transfer_buffer =
-			kzalloc(pdu->u.cmd_submit.transfer_buffer_length,
-				GFP_KERNEL);
-		if (!priv->urb->transfer_buffer) {
+	/* Check if the server's HCD supports SG */
+	if (use_sg && !udev->bus->sg_tablesize) {
+		/*
+		 * If the server's HCD doesn't support SG, break a single SG
+		 * request into several URBs and map each SG list entry to
+		 * corresponding URB buffer. The previously allocated SG
+		 * list is stored in priv->sgl (If the server's HCD support SG,
+		 * SG list is stored only in urb->sg) and it is used as an
+		 * indicator that the server split single SG request into
+		 * several URBs. Later, priv->sgl is used by stub_complete() and
+		 * stub_send_ret_submit() to reassemble the divied URBs.
+		 */
+		support_sg = 0;
+		num_urbs = nents;
+		priv->completed_urbs = 0;
+		pdu->u.cmd_submit.transfer_flags &= ~URB_DMA_MAP_SG;
+	}
+
+	/* allocate urb array */
+	priv->num_urbs = num_urbs;
+	priv->urbs = kmalloc_array(num_urbs, sizeof(*priv->urbs), GFP_KERNEL);
+	if (!priv->urbs)
+		goto err_urbs;
+
+	/* setup a urb */
+	if (support_sg) {
+		if (usb_pipeisoc(pipe))
+			np = pdu->u.cmd_submit.number_of_packets;
+
+		priv->urbs[0] = usb_alloc_urb(np, GFP_KERNEL);
+		if (!priv->urbs[0])
+			goto err_urb;
+
+		if (buf_len) {
+			if (use_sg) {
+				priv->urbs[0]->sg = sgl;
+				priv->urbs[0]->num_sgs = nents;
+				priv->urbs[0]->transfer_buffer = NULL;
+			} else {
+				priv->urbs[0]->transfer_buffer = buffer;
+			}
+		}
+
+		/* copy urb setup packet */
+		priv->urbs[0]->setup_packet = kmemdup(&pdu->u.cmd_submit.setup,
+					8, GFP_KERNEL);
+		if (!priv->urbs[0]->setup_packet) {
 			usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
 			return;
 		}
-	}
 
-	/* copy urb setup packet */
-	priv->urb->setup_packet = kmemdup(&pdu->u.cmd_submit.setup, 8,
-					  GFP_KERNEL);
-	if (!priv->urb->setup_packet) {
-		dev_err(&udev->dev, "allocate setup_packet\n");
-		usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
-		return;
+		usbip_pack_pdu(pdu, priv->urbs[0], USBIP_CMD_SUBMIT, 0);
+	} else {
+		for_each_sg(sgl, sg, nents, i) {
+			priv->urbs[i] = usb_alloc_urb(0, GFP_KERNEL);
+			/* The URBs which is previously allocated will be freed
+			 * in stub_device_cleanup_urbs() if error occurs.
+			 */
+			if (!priv->urbs[i])
+				goto err_urb;
+
+			usbip_pack_pdu(pdu, priv->urbs[i], USBIP_CMD_SUBMIT, 0);
+			priv->urbs[i]->transfer_buffer = sg_virt(sg);
+			priv->urbs[i]->transfer_buffer_length = sg->length;
+		}
+		priv->sgl = sgl;
 	}
 
-	/* set other members from the base header of pdu */
-	priv->urb->context                = (void *) priv;
-	priv->urb->dev                    = udev;
-	priv->urb->pipe                   = pipe;
-	priv->urb->complete               = stub_complete;
+	for (i = 0; i < num_urbs; i++) {
+		/* set other members from the base header of pdu */
+		priv->urbs[i]->context = (void *) priv;
+		priv->urbs[i]->dev = udev;
+		priv->urbs[i]->pipe = pipe;
+		priv->urbs[i]->complete = stub_complete;
 
-	usbip_pack_pdu(pdu, priv->urb, USBIP_CMD_SUBMIT, 0);
+		/* no need to submit an intercepted request, but harmless? */
+		tweak_special_requests(priv->urbs[i]);
 
+		masking_bogus_flags(priv->urbs[i]);
+	}
 
-	if (usbip_recv_xbuff(ud, priv->urb) < 0)
+	if (stub_recv_xbuff(ud, priv) < 0)
 		return;
 
-	if (usbip_recv_iso(ud, priv->urb) < 0)
+	if (usbip_recv_iso(ud, priv->urbs[0]) < 0)
 		return;
 
-	/* no need to submit an intercepted request, but harmless? */
-	tweak_special_requests(priv->urb);
-
-	masking_bogus_flags(priv->urb);
 	/* urb is now ready to submit */
-	ret = usb_submit_urb(priv->urb, GFP_KERNEL);
-
-	if (ret == 0)
-		usbip_dbg_stub_rx("submit urb ok, seqnum %u\n",
-				  pdu->base.seqnum);
-	else {
-		dev_err(&udev->dev, "submit_urb error, %d\n", ret);
-		usbip_dump_header(pdu);
-		usbip_dump_urb(priv->urb);
-
-		/*
-		 * Pessimistic.
-		 * This connection will be discarded.
-		 */
-		usbip_event_add(ud, SDEV_EVENT_ERROR_SUBMIT);
+	for (i = 0; i < priv->num_urbs; i++) {
+		ret = usb_submit_urb(priv->urbs[i], GFP_KERNEL);
+
+		if (ret == 0)
+			usbip_dbg_stub_rx("submit urb ok, seqnum %u\n",
+					pdu->base.seqnum);
+		else {
+			dev_err(&udev->dev, "submit_urb error, %d\n", ret);
+			usbip_dump_header(pdu);
+			usbip_dump_urb(priv->urbs[i]);
+
+			/*
+			 * Pessimistic.
+			 * This connection will be discarded.
+			 */
+			usbip_event_add(ud, SDEV_EVENT_ERROR_SUBMIT);
+			break;
+		}
 	}
 
 	usbip_dbg_stub_rx("Leave\n");
+	return;
+
+err_urb:
+	kfree(priv->urbs);
+err_urbs:
+	kfree(buffer);
+	sgl_free(sgl);
+err_malloc:
+	usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
 }
 
 /* recv a pdu */
diff --git a/drivers/usb/usbip/stub_tx.c b/drivers/usb/usbip/stub_tx.c
index f0ec41a50cbc..36010a82b359 100644
--- a/drivers/usb/usbip/stub_tx.c
+++ b/drivers/usb/usbip/stub_tx.c
@@ -5,25 +5,11 @@
 
 #include <linux/kthread.h>
 #include <linux/socket.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "stub.h"
 
-static void stub_free_priv_and_urb(struct stub_priv *priv)
-{
-	struct urb *urb = priv->urb;
-
-	kfree(urb->setup_packet);
-	urb->setup_packet = NULL;
-
-	kfree(urb->transfer_buffer);
-	urb->transfer_buffer = NULL;
-
-	list_del(&priv->list);
-	kmem_cache_free(stub_priv_cache, priv);
-	usb_free_urb(urb);
-}
-
 /* be in spin_lock_irqsave(&sdev->priv_lock, flags) */
 void stub_enqueue_ret_unlink(struct stub_device *sdev, __u32 seqnum,
 			     __u32 status)
@@ -85,6 +71,22 @@ void stub_complete(struct urb *urb)
 		break;
 	}
 
+	/*
+	 * If the server breaks single SG request into the several URBs, the
+	 * URBs must be reassembled before sending completed URB to the vhci.
+	 * Don't wake up the tx thread until all the URBs are completed.
+	 */
+	if (priv->sgl) {
+		priv->completed_urbs++;
+
+		/* Only save the first error status */
+		if (urb->status && !priv->urb_status)
+			priv->urb_status = urb->status;
+
+		if (priv->completed_urbs < priv->num_urbs)
+			return;
+	}
+
 	/* link a urb to the queue of tx. */
 	spin_lock_irqsave(&sdev->priv_lock, flags);
 	if (sdev->ud.tcp_socket == NULL) {
@@ -156,18 +158,22 @@ static int stub_send_ret_submit(struct stub_device *sdev)
 	size_t total_size = 0;
 
 	while ((priv = dequeue_from_priv_tx(sdev)) != NULL) {
-		int ret;
-		struct urb *urb = priv->urb;
+		struct urb *urb = priv->urbs[0];
 		struct usbip_header pdu_header;
 		struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 		struct kvec *iov = NULL;
+		struct scatterlist *sg;
+		u32 actual_length = 0;
 		int iovnum = 0;
+		int ret;
+		int i;
 
 		txsize = 0;
 		memset(&pdu_header, 0, sizeof(pdu_header));
 		memset(&msg, 0, sizeof(msg));
 
-		if (urb->actual_length > 0 && !urb->transfer_buffer) {
+		if (urb->actual_length > 0 && !urb->transfer_buffer &&
+		   !urb->num_sgs) {
 			dev_err(&sdev->udev->dev,
 				"urb: actual_length %d transfer_buffer null\n",
 				urb->actual_length);
@@ -176,6 +182,11 @@ static int stub_send_ret_submit(struct stub_device *sdev)
 
 		if (usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS)
 			iovnum = 2 + urb->number_of_packets;
+		else if (usb_pipein(urb->pipe) && urb->actual_length > 0 &&
+			urb->num_sgs)
+			iovnum = 1 + urb->num_sgs;
+		else if (usb_pipein(urb->pipe) && priv->sgl)
+			iovnum = 1 + priv->num_urbs;
 		else
 			iovnum = 2;
 
@@ -192,6 +203,15 @@ static int stub_send_ret_submit(struct stub_device *sdev)
 		setup_ret_submit_pdu(&pdu_header, urb);
 		usbip_dbg_stub_tx("setup txdata seqnum: %d\n",
 				  pdu_header.base.seqnum);
+
+		if (priv->sgl) {
+			for (i = 0; i < priv->num_urbs; i++)
+				actual_length += priv->urbs[i]->actual_length;
+
+			pdu_header.u.ret_submit.status = priv->urb_status;
+			pdu_header.u.ret_submit.actual_length = actual_length;
+		}
+
 		usbip_header_correct_endian(&pdu_header, 1);
 
 		iov[iovnum].iov_base = &pdu_header;
@@ -200,12 +220,47 @@ static int stub_send_ret_submit(struct stub_device *sdev)
 		txsize += sizeof(pdu_header);
 
 		/* 2. setup transfer buffer */
-		if (usb_pipein(urb->pipe) &&
+		if (usb_pipein(urb->pipe) && priv->sgl) {
+			/* If the server split a single SG request into several
+			 * URBs because the server's HCD doesn't support SG,
+			 * reassemble the split URB buffers into a single
+			 * return command.
+			 */
+			for (i = 0; i < priv->num_urbs; i++) {
+				iov[iovnum].iov_base =
+					priv->urbs[i]->transfer_buffer;
+				iov[iovnum].iov_len =
+					priv->urbs[i]->actual_length;
+				iovnum++;
+			}
+			txsize += actual_length;
+		} else if (usb_pipein(urb->pipe) &&
 		    usb_pipetype(urb->pipe) != PIPE_ISOCHRONOUS &&
 		    urb->actual_length > 0) {
-			iov[iovnum].iov_base = urb->transfer_buffer;
-			iov[iovnum].iov_len  = urb->actual_length;
-			iovnum++;
+			if (urb->num_sgs) {
+				unsigned int copy = urb->actual_length;
+				int size;
+
+				for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+					if (copy == 0)
+						break;
+
+					if (copy < sg->length)
+						size = copy;
+					else
+						size = sg->length;
+
+					iov[iovnum].iov_base = sg_virt(sg);
+					iov[iovnum].iov_len = size;
+
+					iovnum++;
+					copy -= size;
+				}
+			} else {
+				iov[iovnum].iov_base = urb->transfer_buffer;
+				iov[iovnum].iov_len  = urb->actual_length;
+				iovnum++;
+			}
 			txsize += urb->actual_length;
 		} else if (usb_pipein(urb->pipe) &&
 			   usb_pipetype(urb->pipe) == PIPE_ISOCHRONOUS) {
diff --git a/drivers/usb/usbip/usbip_common.c b/drivers/usb/usbip/usbip_common.c
index 45da3e01c7b0..6532d68e8808 100644
--- a/drivers/usb/usbip/usbip_common.c
+++ b/drivers/usb/usbip/usbip_common.c
@@ -680,8 +680,12 @@ EXPORT_SYMBOL_GPL(usbip_pad_iso);
 /* some members of urb must be substituted before. */
 int usbip_recv_xbuff(struct usbip_device *ud, struct urb *urb)
 {
-	int ret;
+	struct scatterlist *sg;
+	int ret = 0;
+	int recv;
 	int size;
+	int copy;
+	int i;
 
 	if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC) {
 		/* the direction of urb must be OUT. */
@@ -701,29 +705,48 @@ int usbip_recv_xbuff(struct usbip_device *ud, struct urb *urb)
 	if (!(size > 0))
 		return 0;
 
-	if (size > urb->transfer_buffer_length) {
+	if (size > urb->transfer_buffer_length)
 		/* should not happen, probably malicious packet */
-		if (ud->side == USBIP_STUB) {
-			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
-			return 0;
-		} else {
-			usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
-			return -EPIPE;
-		}
-	}
+		goto error;
 
-	ret = usbip_recv(ud->tcp_socket, urb->transfer_buffer, size);
-	if (ret != size) {
-		dev_err(&urb->dev->dev, "recv xbuf, %d\n", ret);
-		if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC) {
-			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
-		} else {
-			usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
-			return -EPIPE;
+	if (urb->num_sgs) {
+		copy = size;
+		for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+			int recv_size;
+
+			if (copy < sg->length)
+				recv_size = copy;
+			else
+				recv_size = sg->length;
+
+			recv = usbip_recv(ud->tcp_socket, sg_virt(sg),
+						recv_size);
+
+			if (recv != recv_size)
+				goto error;
+
+			copy -= recv;
+			ret += recv;
 		}
+
+		if (ret != size)
+			goto error;
+	} else {
+		ret = usbip_recv(ud->tcp_socket, urb->transfer_buffer, size);
+		if (ret != size)
+			goto error;
 	}
 
 	return ret;
+
+error:
+	dev_err(&urb->dev->dev, "recv xbuf, %d\n", ret);
+	if (ud->side == USBIP_STUB || ud->side == USBIP_VUDC)
+		usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
+	else
+		usbip_event_add(ud, VDEV_EVENT_ERROR_TCP);
+
+	return -EPIPE;
 }
 EXPORT_SYMBOL_GPL(usbip_recv_xbuff);
 
diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index 429e4e989f38..0958024b8fae 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c
@@ -697,7 +697,8 @@ static int vhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
 	}
 	vdev = &vhci_hcd->vdev[portnum-1];
 
-	if (!urb->transfer_buffer && urb->transfer_buffer_length) {
+	if (!urb->transfer_buffer && !urb->num_sgs &&
+	     urb->transfer_buffer_length) {
 		dev_dbg(dev, "Null URB transfer buffer\n");
 		return -EINVAL;
 	}
@@ -1143,6 +1144,15 @@ static int vhci_setup(struct usb_hcd *hcd)
 		hcd->speed = HCD_USB3;
 		hcd->self.root_hub->speed = USB_SPEED_SUPER;
 	}
+
+	/*
+	 * Support SG.
+	 * sg_tablesize is an arbitrary value to alleviate memory pressure
+	 * on the host.
+	 */
+	hcd->self.sg_tablesize = 32;
+	hcd->self.no_sg_constraint = 1;
+
 	return 0;
 }
 
@@ -1296,6 +1306,9 @@ static int vhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 		return -EINVAL;
 	}
 
+	if (urb->num_sgs)
+		urb->transfer_flags |= URB_DMA_MAP_SG;
+
 	return 0;
 }
 
diff --git a/drivers/usb/usbip/vhci_tx.c b/drivers/usb/usbip/vhci_tx.c
index 2fa26d0578d7..865eb1276b6c 100644
--- a/drivers/usb/usbip/vhci_tx.c
+++ b/drivers/usb/usbip/vhci_tx.c
@@ -5,6 +5,7 @@
 
 #include <linux/kthread.h>
 #include <linux/slab.h>
+#include <linux/scatterlist.h>
 
 #include "usbip_common.h"
 #include "vhci.h"
@@ -50,19 +51,23 @@ static struct vhci_priv *dequeue_from_priv_tx(struct vhci_device *vdev)
 
 static int vhci_send_cmd_submit(struct vhci_device *vdev)
 {
+	struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 	struct vhci_priv *priv = NULL;
+	struct scatterlist *sg;
 
 	struct msghdr msg;
-	struct kvec iov[3];
+	struct kvec *iov;
 	size_t txsize;
 
 	size_t total_size = 0;
+	int iovnum;
+	int err = -ENOMEM;
+	int i;
 
 	while ((priv = dequeue_from_priv_tx(vdev)) != NULL) {
 		int ret;
 		struct urb *urb = priv->urb;
 		struct usbip_header pdu_header;
-		struct usbip_iso_packet_descriptor *iso_buffer = NULL;
 
 		txsize = 0;
 		memset(&pdu_header, 0, sizeof(pdu_header));
@@ -72,18 +77,42 @@ static int vhci_send_cmd_submit(struct vhci_device *vdev)
 		usbip_dbg_vhci_tx("setup txdata urb seqnum %lu\n",
 				  priv->seqnum);
 
+		if (urb->num_sgs && usb_pipeout(urb->pipe))
+			iovnum = 2 + urb->num_sgs;
+		else
+			iovnum = 3;
+
+		iov = kcalloc(iovnum, sizeof(*iov), GFP_KERNEL);
+		if (!iov) {
+			usbip_event_add(&vdev->ud, SDEV_EVENT_ERROR_MALLOC);
+			return -ENOMEM;
+		}
+
 		/* 1. setup usbip_header */
 		setup_cmd_submit_pdu(&pdu_header, urb);
 		usbip_header_correct_endian(&pdu_header, 1);
+		iovnum = 0;
 
-		iov[0].iov_base = &pdu_header;
-		iov[0].iov_len  = sizeof(pdu_header);
+		iov[iovnum].iov_base = &pdu_header;
+		iov[iovnum].iov_len  = sizeof(pdu_header);
 		txsize += sizeof(pdu_header);
+		iovnum++;
 
 		/* 2. setup transfer buffer */
 		if (!usb_pipein(urb->pipe) && urb->transfer_buffer_length > 0) {
-			iov[1].iov_base = urb->transfer_buffer;
-			iov[1].iov_len  = urb->transfer_buffer_length;
+			if (urb->num_sgs &&
+				      !usb_endpoint_xfer_isoc(&urb->ep->desc)) {
+				for_each_sg(urb->sg, sg, urb->num_sgs, i) {
+					iov[iovnum].iov_base = sg_virt(sg);
+					iov[iovnum].iov_len = sg->length;
+					iovnum++;
+				}
+			} else {
+				iov[iovnum].iov_base = urb->transfer_buffer;
+				iov[iovnum].iov_len  =
+						urb->transfer_buffer_length;
+				iovnum++;
+			}
 			txsize += urb->transfer_buffer_length;
 		}
 
@@ -95,23 +124,26 @@ static int vhci_send_cmd_submit(struct vhci_device *vdev)
 			if (!iso_buffer) {
 				usbip_event_add(&vdev->ud,
 						SDEV_EVENT_ERROR_MALLOC);
-				return -1;
+				goto err_iso_buffer;
 			}
 
-			iov[2].iov_base = iso_buffer;
-			iov[2].iov_len  = len;
+			iov[iovnum].iov_base = iso_buffer;
+			iov[iovnum].iov_len  = len;
+			iovnum++;
 			txsize += len;
 		}
 
-		ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, 3, txsize);
+		ret = kernel_sendmsg(vdev->ud.tcp_socket, &msg, iov, iovnum,
+				     txsize);
 		if (ret != txsize) {
 			pr_err("sendmsg failed!, ret=%d for %zd\n", ret,
 			       txsize);
-			kfree(iso_buffer);
 			usbip_event_add(&vdev->ud, VDEV_EVENT_ERROR_TCP);
-			return -1;
+			err = -EPIPE;
+			goto err_tx;
 		}
 
+		kfree(iov);
 		kfree(iso_buffer);
 		usbip_dbg_vhci_tx("send txdata\n");
 
@@ -119,6 +151,13 @@ static int vhci_send_cmd_submit(struct vhci_device *vdev)
 	}
 
 	return total_size;
+
+err_tx:
+	kfree(iso_buffer);
+err_iso_buffer:
+	kfree(iov);
+
+	return err;
 }
 
 static struct vhci_unlink *dequeue_from_unlink_tx(struct vhci_device *vdev)
-- 
2.20.1

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