Re: [PATCH net 2/2] macvtap: limit head length of skb allocated

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 12, 2013 at 06:02:57PM +0800, Jason Wang wrote:
> We currently use hdr_len as a hint of head length which is advertised by
> guest. But when guest advertise a very big value, it can lead to an 64K+
> allocating of kmalloc() which has a very high possibility of failure when host
> memory is fragmented or under heavy stress. The huge hdr_len also reduce the
> effect of zerocopy or even disable if a gso skb is linearized in guest.
> 
> To solves those issues, this patch introduces an upper limit (PAGE_SIZE) of the
> head, which guarantees an order 0 allocation each time.
> 
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> The patch was needed for stable.
> ---
>  drivers/net/macvtap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 9dccb1e..7ee6f9d 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -523,6 +523,11 @@ static inline struct sk_buff *macvtap_alloc_skb(struct sock *sk, size_t prepad,
>  						int noblock, int *err)
>  {
>  	struct sk_buff *skb;
> +	int good_linear = SKB_MAX_HEAD(prepad);
> +
> +	/* Don't use huge linear part */
> +	if (linear > good_linear)
> +		linear = good_linear;
>  
>  	/* Under a page?  Don't bother with paged skb. */
>  	if (prepad + len < PAGE_SIZE || !linear)
> -- 
> 1.8.3.2
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/