Re: [PATCH v4 4/4] vhost: add an RPMsg API

Michael S. Tsirkin
2020-08-04T14:29:30Z

On Wed, Jul 22, 2020 at 05:09:27PM +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 a VirtIO server. This patch adds a vhost-based RPMsg
> server implementation.
>
> Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
> ---
> drivers/vhost/Kconfig | 7 +
> drivers/vhost/Makefile | 3 +
> drivers/vhost/rpmsg.c | 375 ++++++++++++++++++++++++++++++++++++
> drivers/vhost/vhost_rpmsg.h | 74 +++++++
> 4 files changed, 459 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 d3688c6afb87..602421bf1d03 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

So this lacks a description line so it does not appear
in menuconfig. How is user supposed to set it?
I added a one-line description.

> + depends on VHOST

Other drivers select VHOST instead. Any reason not to
do it like this here?

> + help
> + Vhost RPMsg API allows vhost drivers to communicate with VirtIO
> + drivers, using the RPMsg over VirtIO protocol.
> +

> 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..d7ab48414224
> --- /dev/null
> +++ b/drivers/vhost/rpmsg.c
> @@ -0,0 +1,375 @@
> +// 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. It provides a set of functions to match the
> + * guest side RPMsg VirtIO API, provided by drivers/rpmsg/virtio_rpmsg_bus.c
> + * These functions handle creation of 2 virtual queues, handling of endpoint
> + * addresses, sending a name-space announcement to the guest as well as any
> + * user messages. This API can be used by any vhost driver to handle RPMsg
> + * specific processing.
> + * Specific 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>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/vhost.h>
> +#include <linux/virtio_rpmsg.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
> + */
> +static int vhost_rpmsg_get_single(struct vhost_virtqueue *vq)
> +{
> + 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] && (out || in != 1)) {

This in != 1 looks like a dependency on a specific message layout.
virtio spec says to avoid these. Using iov iters it's not too hard to do
...

> + vq_err(vq,
> + "%s(): invalid %d input and %d output in response queue\n",
> + __func__, in, out);
> + goto return_buf;
> + }
> +
> + if (vq == &vr->vq[VIRTIO_RPMSG_REQUEST] && (in || out != 1)) {
> + vq_err(vq,
> + "%s(): invalid %d input and %d output in request queue\n",
> + __func__, in, out);
> + goto return_buf;
> + }
> +
> + return head;
> +
> +return_buf:
> + /*
> + * FIXME: might need to return the buffer using vhost_add_used()
> + * or vhost_discard_vq_desc(). vhost_discard_vq_desc() is
> + * described as "being useful for error handling," but it makes
> + * the thus discarded buffers "unseen," so next time we look we
> + * retrieve them again?

Yes. It's your decision what to do on error. if you also signal
an eventfd using vq_err, then discarding will
make it so userspace can poke at ring and hopefully fix it ...

> + */
> + 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;
> + 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_single(vq);
> + if (iter->head == vq->num)
> + iter->head = -EAGAIN;
> +
> + if (iter->head < 0)
> + goto unlock;
> +
> + tmp = vq->iov[0].iov_len;
> + if (tmp < sizeof(iter->rhdr)) {
> + vq_err(vq, "%s(): size %zu too small\n", __func__, tmp);
> + iter->head = -ENOBUFS;
> + goto return_buf;
> + }
> +
> + switch (qid) {
> + case VIRTIO_RPMSG_REQUEST:
> + if (len < 0) {
> + len = tmp - sizeof(iter->rhdr);
> + } else if (tmp < sizeof(iter->rhdr) + len) {
> + iter->head = -ENOBUFS;
> + goto return_buf;
> + }
> +
> + /* len is now the size of the payload */
> + iov_iter_init(&iter->iov_iter, WRITE,
> + vq->iov, 1, sizeof(iter->rhdr) + len);
> +
> + /* 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));
> + iter->head = -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));
> + iter->head = -ENOENT;
> + goto return_buf;
> + }
> +
> + /* Let the endpoint read the payload */
> + if (iter->ept->read) {
> + ssize_t ret = iter->ept->read(vr, iter);
> +
> + if (ret < 0) {
> + iter->head = ret;
> + 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);
> +
> + 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) {
> + iter->head = -ENOENT;
> + goto return_buf;
> + }
> + }
> +
> + if (len < 0) {
> + len = tmp - sizeof(iter->rhdr);
> + } else if (tmp < sizeof(iter->rhdr) + len) {
> + iter->head = -ENOBUFS;
> + goto return_buf;
> + } else {
> + iter->rhdr.len = cpu_to_vhost16(vq, len);
> + }
> +
> + /* len is now the size of the payload */
> + iov_iter_init(&iter->iov_iter, READ, vq->iov, 1, sizeof(iter->rhdr) + len);
> +
> + /* Write the RPMSG header with endpoint addresses */
> + tmp = copy_to_iter(&iter->rhdr, sizeof(iter->rhdr), &iter->iov_iter);
> + if (tmp != sizeof(iter->rhdr)) {
> + iter->head = -EIO;
> + goto return_buf;
> + }
> +
> + /* Let the endpoint write the payload */
> + if (iter->ept && iter->ept->write) {
> + ssize_t ret = iter->ept->write(vr, iter);
> +
> + if (ret < 0) {
> + iter->head = ret;
> + goto return_buf;
> + }
> + }
> +
> + break;
> + }
> +
> + return 0;
> +
> +return_buf:
> + /*
> + * FIXME: vhost_discard_vq_desc() or vhost_add_used(), see comment in
> + * vhost_rpmsg_get_single()
> + */

What's to be done with this FIXME?

> +unlock:
> + vhost_enable_notify(&vr->dev, vq);
> + mutex_unlock(&vq->mutex);
> +
> + return iter->head;
> +}
> +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;
> + }
> +
> + 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;
> +
> + 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),
> + .flags = cpu_to_vhost16(vq, RPMSG_NS_CREATE), /* rpmsg_recv_single() */
> + },
> + };
> + struct rpmsg_ns_msg ns = {
> + .addr = cpu_to_vhost32(vq, src),
> + .flags = cpu_to_vhost32(vq, RPMSG_NS_CREATE), /* for rpmsg_ns_cb() */
> + };
> + 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..30072cecb8a0
> --- /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/uio.h>
> +#include <linux/virtio_rpmsg.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 */
> + /* 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
> --
> 2.27.0