Re: [PATCH RFC 12/15] hw/virtio/vhost-user: send isolation regions to device

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Thu, Jul 23, 2026 at 03:30:11PM -0700, Connor Kite wrote:
> Adds features to fill a vhost_user_set_mem_table message with the
> addresses of isolation memory regions corresponding to bounce buffers
> and vrings.
> 
> Signed-off-by: Connor Kite <connorkite@gmail.com>
> ---
>  hw/virtio/vhost-user.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 79 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 710cf966f8..acabfb7f1c 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -625,6 +625,21 @@ static void vhost_user_fill_msg_region(struct vhost_dev *dev,
>      dst->mmap_offset = mmap_offset;
>  }
>  
> +static void vhost_user_fill_msg_region_iso(VhostUserMemoryRegion *dst,
> +                                           const struct vhost_user *u,
> +                                           const struct vhost_memory_region
> +                                           *iova_reg)
> +{
> +    assert(u != NULL && dst != NULL && iova_reg != NULL);
> +    uint64_t offset;
> +
> +    offset = iova_reg->userspace_addr - u->iso_memory.base_addr;
> +    dst->userspace_addr = iova_reg->userspace_addr;
> +    dst->memory_size = iova_reg->memory_size;
> +    dst->guest_phys_addr = iova_reg->userspace_addr;
> +    dst->mmap_offset = offset;
> +}
> +
>  static int vhost_user_fill_set_mem_table_msg(struct vhost_user *u,
>                                               struct vhost_dev *dev,
>                                               VhostUserMsg *msg,
> @@ -1136,7 +1151,33 @@ static void cleanup_isolation_regions(struct vhost_dev *dev)
>      }
>  }
>  
> -__attribute__((unused))
> +struct iova_tree_traversal_args {

QEMU coding style:

  typedef struct {
      ...
  } IOVATreeTraversalArgs;

> +    VhostUserMsg *msg;
> +    struct vhost_user *u;
> +    int *fds;
> +    size_t *fd_num;

This field is also used to index into msg->payload.memory.regions[], so
"fd_num" is a misnomer. I suggest something like "region_idx" or just
"idx".

> +};
> +
> +static gboolean vhost_user_iova_tree_traverse_funct(gpointer key,
> +                                                    gpointer value,
> +                                                    gpointer data)
> +{
> +    struct iova_tree_traversal_args *args = data;
> +    struct vhost_memory_region msg_region;
> +    VhostUserMemoryRegion region_buffer;
> +    DMAMap *map = key;
> +    args->fds[*args->fd_num] = args->u->iso_memory.iso_fd;
> +
> +    msg_region.guest_phys_addr = map->iova;
> +    msg_region.memory_size = map->size + 1;
> +    msg_region.userspace_addr = map->iova;
> +    vhost_user_fill_msg_region_iso(&region_buffer, args->u, &msg_region);
> +    args->msg->payload.memory.regions[*args->fd_num] = region_buffer;

I'm confused by this code. VhostUserMemoryRegion region_buffer is the
vhost-user protocol struct that is being filled in, but there is also a
struct vhost_memory_region msg_region from the Linux kernel headers?

msg_region and vhost_user_fill_msg_region_iso() make it harder to see
what is going on. Can you open code the region_buffer struct field
assignments instead?

> +    (*args->fd_num)++;
> +
> +    return false;
> +}
> +
>  static int init_isolation_regions(struct vhost_dev *dev,
>                                    VhostUserMsg *msg,
>                                    int *fds, size_t *fd_num)
> @@ -1234,6 +1275,24 @@ static int init_isolation_regions(struct vhost_dev *dev,
>                                        map->translated_addr);
>      }
>  
> +    struct iova_tree_traversal_args args = {
> +        .fd_num = fd_num,
> +        .fds = fds,
> +        .msg = msg,
> +        .u = u
> +    };
> +
> +    vhost_iova_tree_foreach(u->iso_iova_tree,
> +                            vhost_user_iova_tree_traverse_funct, &args);
> +
> +    msg->payload.memory.nregions = *fd_num;
> +
> +    assert(*fd_num != 0);
> +
> +    msg->hdr.size = sizeof(msg->payload.memory.nregions);
> +    msg->hdr.size += sizeof(msg->payload.memory.padding);
> +    msg->hdr.size += *fd_num * sizeof(VhostUserMemoryRegion);
> +
>      return 0;
>  }
>  
> @@ -1241,6 +1300,7 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
>                                      struct vhost_memory *mem)
>  {
>      struct vhost_user *u = dev->opaque;
> +    bool memory_isolation = u->user->memory_isolation;
>      int fds[VHOST_MEMORY_BASELINE_NREGIONS];
>      size_t fd_num = 0;
>      bool do_postcopy = u->postcopy_listen && u->postcopy_fd.handler;
> @@ -1268,6 +1328,24 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
>          msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
>      }
>  
> +    if (memory_isolation) {
> +        ret = init_isolation_regions(dev, &msg, fds, &fd_num);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +
> +        ret = vhost_user_write(dev, &msg, fds, fd_num);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +
> +        if (reply_supported) {
> +            return process_message_reply(dev, &msg);
> +        }
> +
> +        return 0;
> +    }
> +
>      if (config_mem_slots) {
>          ret = vhost_user_add_remove_regions(dev, &msg, reply_supported, false);
>          if (ret < 0) {
> 
> -- 
> 2.43.0
> 

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