Re: [Qemu-devel] [PATCH V4] net: Forbid dealing with packets when VM is not running

[Michael S. Tsirkin]

On Tue, Aug 26, 2014 at 04:06:17PM +0800, zhanghailiang wrote:
> For all NICs(except virtio-net) emulated by qemu,
> Such as e1000, rtl8139, pcnet and ne2k_pci,
> Qemu can still receive packets when VM is not running.
> 
> If this happened in *migration's* last PAUSE VM stage, but
> before the end of the migration, the new receiving packets will possibly dirty
> parts of RAM which has been cached in *iovec*(will be sent asynchronously) and
> dirty parts of new RAM which will be missed.
> This will lead serious network fault in VM.
> 
> To avoid this, we forbid receiving packets in generic net code when
> VM is not running.
> 
> Bug reproduction steps:
> (1) Start a VM which configured at least one NIC
> (2) In VM, open several Terminal and do *Ping IP -i 0.1*
> (3) Migrate the VM repeatedly between two Hosts
> And the *PING* command in VM will very likely fail with message:
> 'Destination HOST Unreachable', the NIC in VM will stay unavailable unless you
> run 'service network restart'
> 
> Signed-off-by: zhanghailiang <address@hidden>

Reviewed-by: Michael S. Tsirkin <address@hidden>

> ---
>  v4:
> - The action of flush queued packets is unnecessary, remove this.
>   (Thanks for the help of Jason Wang and Stefan). 
> 
>  v3:
> - change the 'vmstate' to 'vm_running'
> 
>  v2:
> - remove the superfluous check of nc->received_disabled 
> ---
> 
>  net/net.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/net/net.c b/net/net.c
> index 6d930ea..4cb92c0 100644
> --- a/net/net.c
> +++ b/net/net.c
> @@ -41,6 +41,7 @@
>  #include "qapi-visit.h"
>  #include "qapi/opts-visitor.h"
>  #include "qapi/dealloc-visitor.h"
> +#include "sysemu/sysemu.h"
>  
>  /* Net bridge is currently not supported for W32. */
>  #if !defined(_WIN32)
> @@ -452,6 +453,12 @@ void qemu_set_vnet_hdr_len(NetClientState *nc, int len)
>  
>  int qemu_can_send_packet(NetClientState *sender)
>  {
> +    int vm_running = runstate_is_running();
> +
> +    if (!vm_running) {
> +        return 0;
> +    }
> +
>      if (!sender->peer) {
>          return 1;
>      }
> -- 
> 1.7.12.4
>