Subject: Re: [PATCH net] virtio-net: alloc big buffers also when guest can receive UFO

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 13 Feb 2014 07:15:59 +0200

On Thu, Feb 13, 2014 at 11:02:13AM +0800, Jason Wang wrote:
> On 02/12/2014 07:59 PM, Michael S. Tsirkin wrote:
> > On Wed, Feb 12, 2014 at 01:43:28PM +0800, Jason Wang wrote:
> >> > We should alloc big buffers also when guest can receive UFO
> >> > pakcets. Otherwise the big packets will be truncated when mergeable rx
> >> > buffer is disabled.
> > Not truncated, they will be dropped.
> >
> 
> Why dropped? We enable the ufo on tap0 if VIRTIO_NET_F_GUEST_UFO is
> negotiated. So skb was queued on the receive queue. But since the
> receive buffer is small, it will be truncated during tun_put_user().

Hypervisor shouldn't truncate packets silently - if it does
it's a hypervisor bug. Passing malformed packets to guest is
a bad idea.

-- 
MST