Re: [Sound-open-firmware] [PATCH v7 3/3] vhost: add an RPMsg API

18 Sep 2020

Good morning,
On Fri, Sep 18, 2020 at 11:02:29AM +0200, Guennadi Liakhovetski wrote:
...
Hi Mathieu,
On Thu, Sep 17, 2020 at 04:01:38PM -0600, Mathieu Poirier wrote:
...
On Thu, Sep 10, 2020 at 01:13:51PM +0200, Guennadi Liakhovetski wrote:
...
Linux supports running the RPMsg protocol over the VirtIO transport
protocol, but currently there is only support for VirtIO clients and
no support for VirtIO servers. This patch adds a vhost-based RPMsg
server implementation, which makes it possible to use RPMsg over
VirtIO between guest VMs and the host.
I now get the client/server concept you are describing above but that happened
only after a lot of mental gymnastics.  If you drop the whole client/server
concept and concentrate on what this patch does, things will go better.  I would
personally go with what you have in the Kconfig:
...

 Vhost RPMsg API allows vhost drivers to communicate with VirtIO


 drivers on guest VMs, using the RPMsg over VirtIO protocol.



It is concise but describes exactly what this patch provide.
Ok, thanks, will try to improve.
...
...
Signed-off-by: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com
drivers/vhost/Kconfig       |   7 +
 drivers/vhost/Makefile      |   3 +
 drivers/vhost/rpmsg.c       | 370 ++++++++++++++++++++++++++++++++++++
 drivers/vhost/vhost_rpmsg.h |  74 ++++++++
 4 files changed, 454 insertions(+)
 create mode 100644 drivers/vhost/rpmsg.c
 create mode 100644 drivers/vhost/vhost_rpmsg.h

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 587fbae06182..ee1a19b7ab3d 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -38,6 +38,13 @@ config VHOST_NET
     To compile this driver as a module, choose M here: the module will
     be called vhost_net.
+config VHOST_RPMSG

tristate
select VHOST
help
 Vhost RPMsg API allows vhost drivers to communicate with VirtIO


 drivers on guest VMs, using the RPMsg over VirtIO protocol.




I suppose you intend this to be selectable from another config option?
yes.
...
...
config VHOST_SCSI
   tristate "VHOST_SCSI TCM fabric driver"
   depends on TARGET_CORE && EVENTFD
diff --git a/drivers/vhost/Makefile b/drivers/vhost/Makefile
index f3e1897cce85..9cf459d59f97 100644
--- a/drivers/vhost/Makefile
+++ b/drivers/vhost/Makefile
@@ -2,6 +2,9 @@
 obj-$(CONFIG_VHOST_NET) += vhost_net.o
 vhost_net-y := net.o
+obj-$(CONFIG_VHOST_RPMSG) += vhost_rpmsg.o
+vhost_rpmsg-y := rpmsg.o



obj-$(CONFIG_VHOST_SCSI) += vhost_scsi.o
 vhost_scsi-y := scsi.o
diff --git a/drivers/vhost/rpmsg.c b/drivers/vhost/rpmsg.c
new file mode 100644
index 000000000000..0ddee5b5f017
--- /dev/null
+++ b/drivers/vhost/rpmsg.c
@@ -0,0 +1,370 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*


Copyright(c) 2020 Intel Corporation. All rights reserved.







Author: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com







Vhost RPMsg VirtIO interface provides a set of functions to be used on the



host side as a counterpart to the guest side RPMsg VirtIO API, provided by



drivers/rpmsg/virtio_rpmsg_bus.c. This API can be used by any vhost driver to



handle RPMsg specific virtqueue processing.



Vhost drivers, using this API will use their own VirtIO device IDs, that



should then also be added to the ID table in virtio_rpmsg_bus.c


*/


+#include <linux/compat.h>
+#include <linux/file.h>
+#include <linux/miscdevice.h>
As far as I can tell the above two are not needed.
Look like left-over, will remove.
...
...
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/rpmsg/virtio.h>
+#include <linux/vhost.h>
+#include <uapi/linux/rpmsg.h>



+#include "vhost.h"
+#include "vhost_rpmsg.h"



+/*


All virtio-rpmsg virtual queue kicks always come with just one buffer -



either input or output, but we can also handle split messages


*/

+static int vhost_rpmsg_get_msg(struct vhost_virtqueue *vq, unsigned int *cnt)
+{

struct vhost_rpmsg *vr = container_of(vq->dev, struct vhost_rpmsg, dev);
unsigned int out, in;
int head = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in,
		     NULL, NULL);


if (head < 0) {
vq_err(vq, "%s(): error %d getting buffer\n",


       __func__, head);


return head;


}

/* Nothing new? */
if (head == vq->num)
return head;



if (vq == &vr->vq[VIRTIO_RPMSG_RESPONSE]) {
if (out) {


	vq_err(vq, "%s(): invalid %d output in response queue\n",


	       __func__, out);


	goto return_buf;


}



*cnt = in;


}

if (vq == &vr->vq[VIRTIO_RPMSG_REQUEST]) {
if (in) {


	vq_err(vq, "%s(): invalid %d input in request queue\n",


       __func__, in);


	goto return_buf;


}



*cnt = out;


}

return head;


+return_buf:

vhost_add_used(vq, head, 0);

return -EINVAL;

+}



+static const struct vhost_rpmsg_ept *vhost_rpmsg_ept_find(struct vhost_rpmsg *vr, int addr)
+{

unsigned int i;

for (i = 0; i < vr->n_epts; i++)
if (vr->ept[i].addr == addr)


	return vr->ept + i;



return NULL;

+}



+/*


if len < 0, then for reading a request, the complete virtual queue buffer



size is prepared, for sending a response, the length in the iterator is used


*/

+int vhost_rpmsg_start_lock(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

	   unsigned int qid, ssize_t len)


__acquires(vq->mutex)

+{

struct vhost_virtqueue *vq = vr->vq + qid;
unsigned int cnt;
ssize_t ret;
size_t tmp;

if (qid >= VIRTIO_RPMSG_NUM_OF_VQS)
return -EINVAL;



iter->vq = vq;

mutex_lock(&vq->mutex);
vhost_disable_notify(&vr->dev, vq);

iter->head = vhost_rpmsg_get_msg(vq, &cnt);
if (iter->head == vq->num)
iter->head = -EAGAIN;



if (iter->head < 0) {
ret = iter->head;


goto unlock;


}

tmp = iov_length(vq->iov, cnt);
if (tmp < sizeof(iter->rhdr)) {
vq_err(vq, "%s(): size %zu too small\n", __func__, tmp);


ret = -ENOBUFS;


goto return_buf;


}

switch (qid) {
case VIRTIO_RPMSG_REQUEST:
if (len >= 0) {


	if (tmp < sizeof(iter->rhdr) + len) {


		ret = -ENOBUFS;


		goto return_buf;


	}



	tmp = len + sizeof(iter->rhdr);


}



/* len is now the size of the payload */


iov_iter_init(&iter->iov_iter, WRITE, vq->iov, cnt, tmp);



/* Read the RPMSG header with endpoint addresses */


tmp = copy_from_iter(&iter->rhdr, sizeof(iter->rhdr), &iter->iov_iter);


if (tmp != sizeof(iter->rhdr)) {


	vq_err(vq, "%s(): got %zu instead of %zu\n", __func__,


	       tmp, sizeof(iter->rhdr));


	ret = -EIO;


	goto return_buf;


}



iter->ept = vhost_rpmsg_ept_find(vr, vhost32_to_cpu(vq, iter->rhdr.dst));


if (!iter->ept) {


	vq_err(vq, "%s(): no endpoint with address %d\n",


	       __func__, vhost32_to_cpu(vq, iter->rhdr.dst));


	ret = -ENOENT;


	goto return_buf;


}



/* Let the endpoint read the payload */


if (iter->ept->read) {


	ret = iter->ept->read(vr, iter);


	if (ret < 0)


		goto return_buf;



	iter->rhdr.len = cpu_to_vhost16(vq, ret);


} else {


	iter->rhdr.len = 0;


}



/* Prepare for the response phase */


iter->rhdr.dst = iter->rhdr.src;


iter->rhdr.src = cpu_to_vhost32(vq, iter->ept->addr);



I'm a little puzzled here - what will the response look like?  And why is it
prepared here?  From what I can see doing so introduces coupling with function
handle_rpmsg_req_single().  I think confirmation of reception should be handled
by endpoints rather than in the core.
RPMsg always contain a header, so we keep the header in the iterator. If the 
caller wants to reply to the request, the easiest way to do that is to reuse the 
iterator. In that case obviously you have to swap source and destination 
addresses. This can be done either in the request handler of the API, or by the 
caller, or in the API response handler. It would be silly to have the user do 
that, that would be repeated code. But I agree, it's a bit unclean to modify the 
header before returning it to the user, without knowing, whether the user will 
use it, in which case it might be surprised to see most fields from the request 
unchanged and only addresses swapped. I'll move this to response with a check 
for a reused iterator.
...
...


break;


case VIRTIO_RPMSG_RESPONSE:
if (!iter->ept && iter->rhdr.dst != cpu_to_vhost32(vq, RPMSG_NS_ADDR)) {


	/*


	 * Usually the iterator is configured when processing a


	 * message on the request queue, but it's also possible


	 * to send a message on the response queue without a


	 * preceding request, in that case the iterator must


	 * contain source and destination addresses.


	 */


	iter->ept = vhost_rpmsg_ept_find(vr, vhost32_to_cpu(vq, iter->rhdr.src));


	if (!iter->ept) {


		ret = -ENOENT;


		goto return_buf;


	}


}



if (len >= 0) {


	if (tmp < sizeof(iter->rhdr) + len) {


		ret = -ENOBUFS;


		goto return_buf;


	}



	iter->rhdr.len = cpu_to_vhost16(vq, len);


	tmp = len + sizeof(iter->rhdr);


}



/* len is now the size of the payload */


iov_iter_init(&iter->iov_iter, READ, vq->iov, cnt, tmp);



/* Write the RPMSG header with endpoint addresses */


tmp = copy_to_iter(&iter->rhdr, sizeof(iter->rhdr), &iter->iov_iter);


if (tmp != sizeof(iter->rhdr)) {


	ret = -EIO;


	goto return_buf;


}



/* Let the endpoint write the payload */



I would specifically mention that namespace payloads are taken care of by
vhost_rpmsg_ns_announce().  That makes it easier for people to connect the dots.
Ok
...
...

if (iter->ept && iter->ept->write) {


	ret = iter->ept->write(vr, iter);


	if (ret < 0)


		goto return_buf;


}



break;


}

return 0;


+return_buf:

vhost_add_used(vq, iter->head, 0);

+unlock:

vhost_enable_notify(&vr->dev, vq);
mutex_unlock(&vq->mutex);

return ret;

+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_start_lock);



+size_t vhost_rpmsg_copy(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

	void *data, size_t size)



+{

/*
* We could check for excess data, but copy_{to,from}_iter() don't do


* that either


*/


if (iter->vq == vr->vq + VIRTIO_RPMSG_RESPONSE)
return copy_to_iter(data, size, &iter->iov_iter);



return copy_from_iter(data, size, &iter->iov_iter);

+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_copy);



+int vhost_rpmsg_finish_unlock(struct vhost_rpmsg *vr,

	      struct vhost_rpmsg_iter *iter)


__releases(vq->mutex)

+{

if (iter->head >= 0)
vhost_add_used_and_signal(iter->vq->dev, iter->vq, iter->head,


			  vhost16_to_cpu(iter->vq, iter->rhdr.len) +


			  sizeof(iter->rhdr));



vhost_enable_notify(&vr->dev, iter->vq);
mutex_unlock(&iter->vq->mutex);

return iter->head;

+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_finish_unlock);



+/*


Return false to terminate the external loop only if we fail to obtain either



a request or a response buffer


*/

+static bool handle_rpmsg_req_single(struct vhost_rpmsg *vr,

		    struct vhost_virtqueue *vq)



+{

struct vhost_rpmsg_iter iter;
int ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_REQUEST, -EINVAL);
if (!ret)
ret = vhost_rpmsg_finish_unlock(vr, &iter);


if (ret < 0) {
if (ret != -EAGAIN)


	vq_err(vq, "%s(): RPMSG processing failed %d\n",


	       __func__, ret);


return false;


}

if (!iter.ept->write)
return true;



ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_RESPONSE, -EINVAL);
if (!ret)
ret = vhost_rpmsg_finish_unlock(vr, &iter);


if (ret < 0) {
vq_err(vq, "%s(): RPMSG finalising failed %d\n", __func__, ret);


return false;


}

As I said before dealing with the "response" queue here seems to be introducing
coupling with vhost_rpmsg_start_lock()...  Endpoints should be doing that.
Sorry, could you elaborate a bit, what do you mean by coupling?
In function vhost_rpmsg_start_lock() the rpmsg header is prepared for a response
at the end of the processing associated with the reception of a
VIRTIO_RPMSG_REQUEST.  I assumed (perhaps wrongly) that such as response was
sent here.  In that case preparing the response and sending the response should
be done at the same place.
But my assumption may be completely wrong... A better question should probably
be why is the VIRTIO_RPMSG_RESPONSE probed in handle_rpmsg_req_single()?
Shouldn't this be solely concerned with handling requests from the guest?  If
I'm wondering what is going on I expect other people will also do the same,
something that could be alleviated with more comments.
Thanks,
Mathieu
...
...
...


return true;

+}



+static void handle_rpmsg_req_kick(struct vhost_work *work)
+{

struct vhost_virtqueue *vq = container_of(work, struct vhost_virtqueue,
				  poll.work);


struct vhost_rpmsg *vr = container_of(vq->dev, struct vhost_rpmsg, dev);

while (handle_rpmsg_req_single(vr, vq))
;



+}



+/*


initialise two virtqueues with an array of endpoints,



request and response callbacks


*/

+void vhost_rpmsg_init(struct vhost_rpmsg *vr, const struct vhost_rpmsg_ept *ept,

      unsigned int n_epts)



+{

unsigned int i;

for (i = 0; i < ARRAY_SIZE(vr->vq); i++)
vr->vq_p[i] = &vr->vq[i];



/* vq[0]: host -> guest, vq[1]: host <- guest */
vr->vq[VIRTIO_RPMSG_REQUEST].handle_kick = handle_rpmsg_req_kick;
vr->vq[VIRTIO_RPMSG_RESPONSE].handle_kick = NULL;

The comment depicts vq[0] followed by vq[1] but the code initialise vq[1] before
vq[0], which is wildly confusing.  At the very least this should be:
Nobody should care which of those is 0 and which is 1 :-) But indeed you have a point, 
that the protocol isn't strictly request-response based, the host can also send 
messages to the guest without preceding requests. So, TX / RX should be a better fit.
...
vr->vq[VIRTIO_RPMSG_RESPONSE].handle_kick = NULL;
   vr->vq[VIRTIO_RPMSG_REQUEST].handle_kick = handle_rpmsg_req_kick;
And even better:
    /* See configuration of *vq_cbs[] in rpmsg_probe()  */

vr->vq[VIRTIO_RPMSG_TX].handle_kick = NULL;
   vr->vq[VIRTIO_RPMSG_RX].handle_kick = handle_rpmsg_req_kick;
...


vr->ept = ept;
vr->n_epts = n_epts;

vhost_dev_init(&vr->dev, vr->vq_p, VIRTIO_RPMSG_NUM_OF_VQS,
       UIO_MAXIOV, 0, 0, true, NULL);



+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_init);



+void vhost_rpmsg_destroy(struct vhost_rpmsg *vr)
+{

if (vhost_dev_has_owner(&vr->dev))
vhost_poll_flush(&vr->vq[VIRTIO_RPMSG_REQUEST].poll);



vhost_dev_cleanup(&vr->dev);

+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_destroy);



+/* send namespace */
+int vhost_rpmsg_ns_announce(struct vhost_rpmsg *vr, const char *name, unsigned int src)
+{

struct vhost_virtqueue *vq = &vr->vq[VIRTIO_RPMSG_RESPONSE];
struct vhost_rpmsg_iter iter = {
.rhdr = {


	.src = 0,


	.dst = cpu_to_vhost32(vq, RPMSG_NS_ADDR),


},


};
struct rpmsg_ns_msg ns = {
.addr = cpu_to_vhost32(vq, src),


.flags = cpu_to_vhost32(vq, RPMSG_NS_CREATE), /* for rpmsg_ns_cb() */


};

Here we have to assume the source can be found in the endpoints registered in
vhost_rpmsg_init().  I would put a check to make sure that is the case and
return an error otherwise.
Ok, will do.
...
...

int ret = vhost_rpmsg_start_lock(vr, &iter, VIRTIO_RPMSG_RESPONSE, sizeof(ns));

if (ret < 0)
return ret;



strlcpy(ns.name, name, sizeof(ns.name));

ret = vhost_rpmsg_copy(vr, &iter, &ns, sizeof(ns));
if (ret != sizeof(ns))
vq_err(iter.vq, "%s(): added %d instead of %zu bytes\n",


       __func__, ret, sizeof(ns));



ret = vhost_rpmsg_finish_unlock(vr, &iter);
if (ret < 0)
vq_err(iter.vq, "%s(): namespace announcement failed: %d\n",


       __func__, ret);



return ret;

+}
+EXPORT_SYMBOL_GPL(vhost_rpmsg_ns_announce);



+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Intel, Inc.");
+MODULE_DESCRIPTION("Vhost RPMsg API");
diff --git a/drivers/vhost/vhost_rpmsg.h b/drivers/vhost/vhost_rpmsg.h
new file mode 100644
index 000000000000..c020ea14cd16
--- /dev/null
+++ b/drivers/vhost/vhost_rpmsg.h
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*


Copyright(c) 2020 Intel Corporation. All rights reserved.







Author: Guennadi Liakhovetski guennadi.liakhovetski@linux.intel.com


*/


+#ifndef VHOST_RPMSG_H
+#define VHOST_RPMSG_H



+#include <linux/rpmsg/virtio.h>
+#include <linux/uio.h>



+#include "vhost.h"



+/* RPMsg uses two VirtQueues: one for each direction */
+enum {

VIRTIO_RPMSG_RESPONSE,	/* RPMsg response (host->guest) buffers */
VIRTIO_RPMSG_REQUEST,	/* RPMsg request (guest->host) buffers */

As I said above things would be much clearer if this was VIRTIO_RPMSG_TX and
VIRTIO_RPMSG_RX.
Ack.
...
I won't be commenting on the mechanic needed to access and send information on
the virtqueues as it is completely foreign to me.  Other than the above I think
this is going somewhere.
I'll wait for your clarifications about "coupling" and send a v8.
Thanks for the comments so far
Guennadi
...
Thanks,
Mathieu
...

/* Keep last */
VIRTIO_RPMSG_NUM_OF_VQS,

+};



+struct vhost_rpmsg_ept;



+struct vhost_rpmsg_iter {

struct iov_iter iov_iter;
struct rpmsg_hdr rhdr;
struct vhost_virtqueue *vq;
const struct vhost_rpmsg_ept *ept;
int head;
void *priv;

+};



+struct vhost_rpmsg {

struct vhost_dev dev;
struct vhost_virtqueue vq[VIRTIO_RPMSG_NUM_OF_VQS];
struct vhost_virtqueue *vq_p[VIRTIO_RPMSG_NUM_OF_VQS];
const struct vhost_rpmsg_ept *ept;
unsigned int n_epts;

+};



+struct vhost_rpmsg_ept {

ssize_t (*read)(struct vhost_rpmsg *, struct vhost_rpmsg_iter *);
ssize_t (*write)(struct vhost_rpmsg *, struct vhost_rpmsg_iter *);
int addr;

+};



+static inline size_t vhost_rpmsg_iter_len(const struct vhost_rpmsg_iter *iter)
+{

return iter->rhdr.len;

+}



+#define VHOST_RPMSG_ITER(_vq, _src, _dst) {			\

.rhdr = {						\
	.src = cpu_to_vhost32(_vq, _src),	\


	.dst = cpu_to_vhost32(_vq, _dst),	\


},						\


}


+void vhost_rpmsg_init(struct vhost_rpmsg *vr, const struct vhost_rpmsg_ept *ept,

      unsigned int n_epts);



+void vhost_rpmsg_destroy(struct vhost_rpmsg *vr);
+int vhost_rpmsg_ns_announce(struct vhost_rpmsg *vr, const char *name,

	    unsigned int src);



+int vhost_rpmsg_start_lock(struct vhost_rpmsg *vr,

	   struct vhost_rpmsg_iter *iter,


	   unsigned int qid, ssize_t len);



+size_t vhost_rpmsg_copy(struct vhost_rpmsg *vr, struct vhost_rpmsg_iter *iter,

	void *data, size_t size);



+int vhost_rpmsg_finish_unlock(struct vhost_rpmsg *vr,

	      struct vhost_rpmsg_iter *iter);




+#endif
2.28.0

    