Re: [RFC PATCH v7 19/25] vhost: Add vhost_svq_inject

[Jason Wang]

On Thu, Apr 14, 2022 at 12:32 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> This allows qemu to inject packets to the device without guest's notice.

Does it mean it can support guests without _F_ANNOUNCE?

>
> This will be use to inject net CVQ messages to restore status in the 
> destination

I guess for restoring, we should set cvq.ready = true but all other
(TX/RX) as false before we complete the restoring? If yes, I don't see
codes to do that.

>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-shadow-virtqueue.h |   5 +
>  hw/virtio/vhost-shadow-virtqueue.c | 179 +++++++++++++++++++++++++----
>  2 files changed, 160 insertions(+), 24 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> b/hw/virtio/vhost-shadow-virtqueue.h
> index e06ac52158..2a5229e77f 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -17,6 +17,9 @@
>
>  typedef struct SVQElement {
>      VirtQueueElement elem;
> +    hwaddr in_iova;
> +    hwaddr out_iova;
> +    bool not_from_guest;

Let's add a comment for those fields.

>  } SVQElement;
>
>  typedef void (*VirtQueueElementCallback)(VirtIODevice *vdev,
> @@ -106,6 +109,8 @@ typedef struct VhostShadowVirtqueue {
>
>  bool vhost_svq_valid_features(uint64_t features, Error **errp);
>
> +bool vhost_svq_inject(VhostShadowVirtqueue *svq, const struct iovec *iov,
> +                      size_t out_num, size_t in_num);
>  void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
>  void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd);
>  void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index 87980e2a9c..f3600df133 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -16,6 +16,7 @@
>  #include "qemu/log.h"
>  #include "qemu/memalign.h"
>  #include "linux-headers/linux/vhost.h"
> +#include "qemu/iov.h"
>
>  /**
>   * Validate the transport device features that both guests can use with the 
> SVQ
> @@ -122,7 +123,8 @@ static bool vhost_svq_translate_addr(const 
> VhostShadowVirtqueue *svq,
>      return true;
>  }
>
> -static bool vhost_svq_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr 
> *sg,
> +static bool vhost_svq_vring_write_descs(VhostShadowVirtqueue *svq,
> +                                        SVQElement *svq_elem, hwaddr *sg,
>                                          const struct iovec *iovec, size_t 
> num,
>                                          bool more_descs, bool write)
>  {
> @@ -130,15 +132,39 @@ static bool 
> vhost_svq_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr *sg,
>      unsigned n;
>      uint16_t flags = write ? cpu_to_le16(VRING_DESC_F_WRITE) : 0;
>      vring_desc_t *descs = svq->vring.desc;
> -    bool ok;
>
>      if (num == 0) {
>          return true;
>      }
>
> -    ok = vhost_svq_translate_addr(svq, sg, iovec, num);
> -    if (unlikely(!ok)) {
> -        return false;
> +    if (svq_elem->not_from_guest) {
> +        DMAMap map = {
> +            .translated_addr = (hwaddr)iovec->iov_base,
> +            .size = ROUND_UP(iovec->iov_len, 4096) - 1,
> +            .perm = write ? IOMMU_RW : IOMMU_RO,
> +        };
> +        int r;
> +
> +        if (unlikely(num != 1)) {
> +            error_report("Unexpected chain of element injected");
> +            return false;
> +        }
> +        r = vhost_iova_tree_map_alloc(svq->iova_tree, &map);
> +        if (unlikely(r != IOVA_OK)) {
> +            error_report("Cannot map injected element");
> +            return false;
> +        }
> +
> +        r = svq->map_ops->map(map.iova, map.size + 1,
> +                              (void *)map.translated_addr, !write,
> +                              svq->map_ops_opaque);
> +        assert(r == 0);
> +        sg[0] = map.iova;
> +    } else {
> +        bool ok = vhost_svq_translate_addr(svq, sg, iovec, num);
> +        if (unlikely(!ok)) {
> +            return false;
> +        }
>      }
>
>      for (n = 0; n < num; n++) {
> @@ -166,7 +192,8 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue 
> *svq, SVQElement *svq_elem,
>      unsigned avail_idx;
>      vring_avail_t *avail = svq->vring.avail;
>      bool ok;
> -    g_autofree hwaddr *sgs = g_new(hwaddr, MAX(elem->out_num, elem->in_num));
> +    g_autofree hwaddr *sgs = NULL;
> +    hwaddr *in_sgs, *out_sgs;
>
>      *head = svq->free_head;
>
> @@ -177,15 +204,23 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue 
> *svq, SVQElement *svq_elem,
>          return false;
>      }
>
> -    ok = vhost_svq_vring_write_descs(svq, sgs, elem->out_sg, elem->out_num,
> -                                     elem->in_num > 0, false);
> +    if (!svq_elem->not_from_guest) {
> +        sgs = g_new(hwaddr, MAX(elem->out_num, elem->in_num));
> +        in_sgs = out_sgs = sgs;
> +    } else {
> +        in_sgs = &svq_elem->in_iova;
> +        out_sgs = &svq_elem->out_iova;
> +    }
> +    ok = vhost_svq_vring_write_descs(svq, svq_elem, out_sgs, elem->out_sg,
> +                                     elem->out_num, elem->in_num > 0, false);
>      if (unlikely(!ok)) {
>          return false;
>      }
>
> -    ok = vhost_svq_vring_write_descs(svq, sgs, elem->in_sg, elem->in_num, 
> false,
> -                                     true);
> +    ok = vhost_svq_vring_write_descs(svq, svq_elem, in_sgs, elem->in_sg,
> +                                     elem->in_num, false, true);
>      if (unlikely(!ok)) {
> +        /* TODO unwind out_sg */
>          return false;
>      }
>
> @@ -230,6 +265,43 @@ static void vhost_svq_kick(VhostShadowVirtqueue *svq)
>      event_notifier_set(&svq->hdev_kick);
>  }
>
> +bool vhost_svq_inject(VhostShadowVirtqueue *svq, const struct iovec *iov,
> +                      size_t out_num, size_t in_num)
> +{
> +    size_t out_size = iov_size(iov, out_num);
> +    size_t out_buf_size = ROUND_UP(out_size, 4096);
> +    size_t in_size = iov_size(iov + out_num, in_num);
> +    size_t in_buf_size = ROUND_UP(in_size, 4096);
> +    SVQElement *svq_elem;
> +    uint16_t num_slots = (in_num ? 1 : 0) + (out_num ? 1 : 0);
> +
> +    if (unlikely(num_slots == 0 || svq->next_guest_avail_elem ||
> +                 vhost_svq_available_slots(svq) < num_slots)) {
> +        return false;
> +    }
> +
> +    svq_elem = virtqueue_alloc_element(sizeof(SVQElement), 1, 1);
> +    if (out_num) {
> +        void *out = qemu_memalign(4096, out_buf_size);
> +        svq_elem->elem.out_sg[0].iov_base = out;
> +        svq_elem->elem.out_sg[0].iov_len = out_size;
> +        iov_to_buf(iov, out_num, 0, out, out_size);
> +        memset(out + out_size, 0, out_buf_size - out_size);
> +    }
> +    if (in_num) {
> +        void *in = qemu_memalign(4096, in_buf_size);
> +        svq_elem->elem.in_sg[0].iov_base = in;
> +        svq_elem->elem.in_sg[0].iov_len = in_size;
> +        memset(in, 0, in_buf_size);
> +    }
> +
> +    svq_elem->not_from_guest = true;
> +    vhost_svq_add(svq, svq_elem);
> +    vhost_svq_kick(svq);
> +

Should we wait for the completion before moving forward? Otherwise we
will have a race.

And if we wait for the completion (e.g doing busy polling), I think we
can avoid the auxiliary structures like
in_iova/out_iova/not_from_guest by doing mapping before
vhost_svq_add() to keep it clean.

Thanks

> +    return true;
> +}
> +
>  /**
>   * Forward available buffers.
>   *
> @@ -267,6 +339,7 @@ static void vhost_handle_guest_kick(VhostShadowVirtqueue 
> *svq)
>                  break;
>              }
>
> +            svq_elem->not_from_guest = false;
>              elem = &svq_elem->elem;
>              if (elem->out_num + elem->in_num > 
> vhost_svq_available_slots(svq)) {
>                  /*
> @@ -391,6 +464,31 @@ static SVQElement 
> *vhost_svq_get_buf(VhostShadowVirtqueue *svq, uint32_t *len)
>      return g_steal_pointer(&svq->ring_id_maps[used_elem.id]);
>  }
>
> +static int vhost_svq_unmap(VhostShadowVirtqueue *svq, hwaddr iova, size_t 
> size)
> +{
> +    DMAMap needle = {
> +        .iova = iova,
> +        .size = size,
> +    };
> +    const DMAMap *overlap;
> +
> +    while ((overlap = vhost_iova_tree_find(svq->iova_tree, &needle))) {
> +        DMAMap needle = *overlap;
> +
> +        if (svq->map_ops->unmap) {
> +            int r = svq->map_ops->unmap(overlap->iova, overlap->size + 1,
> +                                        svq->map_ops_opaque);
> +            if (unlikely(r != 0)) {
> +                return r;
> +            }
> +        }
> +        qemu_vfree((void *)overlap->translated_addr);
> +        vhost_iova_tree_remove(svq->iova_tree, &needle);
> +    }
> +
> +    return 0;
> +}
> +
>  static void vhost_svq_flush(VhostShadowVirtqueue *svq,
>                              bool check_for_avail_queue)
>  {
> @@ -410,23 +508,56 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
>              }
>
>              elem = &svq_elem->elem;
> -            if (unlikely(i >= svq->vring.num)) {
> -                qemu_log_mask(LOG_GUEST_ERROR,
> -                         "More than %u used buffers obtained in a %u size 
> SVQ",
> -                         i, svq->vring.num);
> -                virtqueue_fill(vq, elem, len, i);
> -                virtqueue_flush(vq, i);
> -                return;
> -            }
> -            virtqueue_fill(vq, elem, len, i++);
> -
>              if (svq->ops && svq->ops->used_elem_handler) {
>                  svq->ops->used_elem_handler(svq->vdev, elem);
>              }
> +
> +            if (svq_elem->not_from_guest) {
> +                if (unlikely(!elem->out_num && elem->out_num != 1)) {
> +                    error_report("Unexpected out_num > 1");
> +                    return;
> +                }
> +
> +                if (elem->out_num) {
> +                    int r = vhost_svq_unmap(svq, svq_elem->out_iova,
> +                                            elem->out_sg[0].iov_len);
> +                    if (unlikely(r != 0)) {
> +                        error_report("Cannot unmap out buffer");
> +                        return;
> +                    }
> +                }
> +
> +                if (unlikely(!elem->in_num && elem->in_num != 1)) {
> +                    error_report("Unexpected in_num > 1");
> +                    return;
> +                }
> +
> +                if (elem->in_num) {
> +                    int r = vhost_svq_unmap(svq, svq_elem->in_iova,
> +                                            elem->in_sg[0].iov_len);
> +                    if (unlikely(r != 0)) {
> +                        error_report("Cannot unmap out buffer");
> +                        return;
> +                    }
> +                }
> +            } else {
> +                if (unlikely(i >= svq->vring.num)) {
> +                    qemu_log_mask(
> +                        LOG_GUEST_ERROR,
> +                        "More than %u used buffers obtained in a %u size 
> SVQ",
> +                        i, svq->vring.num);
> +                    virtqueue_fill(vq, elem, len, i);
> +                    virtqueue_flush(vq, i);
> +                    return;
> +                }
> +                virtqueue_fill(vq, elem, len, i++);
> +            }
>          }
>
> -        virtqueue_flush(vq, i);
> -        event_notifier_set(&svq->svq_call);
> +        if (i > 0) {
> +            virtqueue_flush(vq, i);
> +            event_notifier_set(&svq->svq_call);
> +        }
>
>          if (check_for_avail_queue && svq->next_guest_avail_elem) {
>              /*
> @@ -590,13 +721,13 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
>      for (unsigned i = 0; i < svq->vring.num; ++i) {
>          g_autofree SVQElement *svq_elem = NULL;
>          svq_elem = g_steal_pointer(&svq->ring_id_maps[i]);
> -        if (svq_elem) {
> +        if (svq_elem && !svq_elem->not_from_guest) {
>              virtqueue_detach_element(svq->vq, &svq_elem->elem, 0);
>          }
>      }
>
>      next_avail_elem = g_steal_pointer(&svq->next_guest_avail_elem);
> -    if (next_avail_elem) {
> +    if (next_avail_elem && !next_avail_elem->not_from_guest) {
>          virtqueue_detach_element(svq->vq, &next_avail_elem->elem, 0);
>      }
>      svq->vq = NULL;
> --
> 2.27.0
>