netdev - Re: [PATCH] xen-netfront: Fix handling packets on compound pages with skb

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Date:	Sat, 02 Aug 2014 15:33:37 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	wei.liu2@...rix.com
Cc:	zoltan.kiss@...rix.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	Ian.Campbell@...rix.com, paul.durrant@...rix.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen-netfront: Fix handling packets on compound pages
 with skb_segment

From: Wei Liu <wei.liu2@...rix.com>
Date: Fri, 1 Aug 2014 12:02:46 +0100

> On Thu, Jul 31, 2014 at 01:25:20PM -0700, David Miller wrote:
>> If you were to have a 64-slot TX queue, you ought to be able to handle
>> this theoretical 51 slot SKB.
> 
> There's two problems:
> 1. IIRC a single page ring has 256 slots, allowing 64 slots packet
>    yields 4 in-flight packets in worst case.
> 2. Older netback could not handle this large number of slots and it's
>    likely to deem the frontend malicious.
> 
> For #1, we don't actually care that much if guest screws itself by
> generating 64 slot packets. #2 is more concerning.

How many slots can the older netback handle?
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