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

On 24.07.26 00:30, 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 <[email protected]>
> ---
>   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 {
> +    VhostUserMsg *msg;
> +    struct vhost_user *u;
> +    int *fds;
> +    size_t *fd_num;
> +};
> +
> +static gboolean vhost_user_iova_tree_traverse_funct(gpointer key,
> +                                                    gpointer value,
> +                                                    gpointer data)

This function name doesn’t really say what the function does, and more 
describes its type.

> +{
> +    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;

Generally: I find it quite hard to read code where general statements 
come after a list of declarations without an empty line, especially if 
there is an empty line later. Visually, this last line to me looks like 
another variable declaration.

> +
> +    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;

Why does `vhost_user_fill_msg_region_iso()` exist when this is the only 
caller, and we could just fill `regions[i]` here directly?

> +    (*args->fd_num)++;

As noted by Akihiko, there needs to be some bounds checking. At least 
against `VHOST_MEMORY_BASELINE_NREGIONS`, but even better against the 
array size of `args->msg->payload.memory.regions` and the caller should 
pass the size of `fds[]` via `args`.

(And I’m also with Stefan, something with `index` would be better. Maybe 
`region_idx`.)

> +
> +    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
> +    };

Personal preference: I would like `*fd_num = 0` somewhere here, or 
`assert(*fd_num == 0)` before the iteration. Yes, the caller initializes 
it to zero, but it is just not obvious here, and it seems necessary for 
correct semantics.

(And the open question whether `fd_num` should be renamed here, too, or 
can keep that name. Not sure.)

> +
> +    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);

Am I wrong or should `*fd_num == nregions`? Is it possible that 
`*fd_num` is less because regions end up joined? Can you add a comment 
on when they would differ?

Hanna

> +
> +    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;
>   }

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