Re: [Qemu-devel] [PATCH v5 1/4] vhost: remove assertion to prevent crash

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 10 Jan 2018 00:39:35 +0800
Jay Zhou <jianjay.zhou@huawei.com> wrote:

> Start QEMU with more DIMM devices than limit but without any
> vhost backends and then hotplug a vhost user backend, the VM
> will be crashed.
> Instead of asserting in vhost_user_set_mem_table(), error number
> is used to gracefully prevent device to start. This fixes the
> crash issue.

I'd rewrite commit message as following:
--
QEMU will assert on vhsot-user backed virtio device hotplug
if QEMU is using more RAM regions than VHOST_MEMORY_MAX_NREGIONS
(for example if it  were started with a lot of DIMM devices).

Fix it by returning error instead of asserting and let
callers of vhost_set_mem_table() handle error condition
gracefully.
--

>
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Jay Zhou <jianjay.zhou@huawei.com>
> ---
>  hw/virtio/vhost-user.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 093675e..8500562 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -317,11 +317,14 @@ static int vhost_user_set_mem_table(struct vhost_dev *dev,
>                                       &offset);
>          fd = memory_region_get_fd(mr);
>          if (fd > 0) {
> +            if (fd_num == VHOST_MEMORY_MAX_NREGIONS) {
> +                error_report("Failed preparing vhost-user memory table msg");
> +                return -1;
> +            }
>              msg.payload.memory.regions[fd_num].userspace_addr = reg->userspace_addr;
>              msg.payload.memory.regions[fd_num].memory_size  = reg->memory_size;
>              msg.payload.memory.regions[fd_num].guest_phys_addr = reg->guest_phys_addr;
>              msg.payload.memory.regions[fd_num].mmap_offset = offset;
> -            assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
>              fds[fd_num++] = fd;
>          }
>      }