Message-ID: <4FB62009.2050900@redhat.com>
Date: Fri, 18 May 2012 18:10:17 +0800
From: Jason Wang <jasowang@redhat.com>
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To: Shirley Ma <mashirle@us.ibm.com>
CC: eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, ebiederm@xmission.com,
        davem@davemloft.net
Subject: Re: [V2 PATCH 2/9] macvtap: zerocopy: fix truesize underestimation
References: <20120502033901.11782.13157.stgit@amd-6168-8-1.englab.nay.redhat.com>  <20120502034144.11782.88947.stgit@amd-6168-8-1.englab.nay.redhat.com>  <1337102809.8220.10.camel@oc3660625478.ibm.com>  <4FB3192E.4030803@redhat.com>  <1337180585.10741.6.camel@oc3660625478.ibm.com>  <4FB469A1.3040507@redhat.com> <1337268512.10741.53.camel@oc3660625478.ibm.com>
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On 05/17/2012 11:28 PM, Shirley Ma wrote:
> On Thu, 2012-05-17 at 10:59 +0800, Jason Wang wrote:
>> Didn't see how this affact skb->len. And for truesize, I think they
>> are
>> different, when the offset were not zero, the data in this vector
>> were
>> divided into two parts. First part is copied into skb directly, and
>> the
>> second were pinned from a whole userspace page by
>> get_user_pages_fast(),
>> so we need count the whole page to the socket limit to prevent evil
>> application.
> What I meant that the code for skb->truesize has double added the first
> offset if any left from that vector (partically copied into skb
> directly, and then count pagesize which includes the offset (truesize +=
> PAGE_SIZE)).

Yes, I get you mean. There's no difference between first frag and 
others: it's also possible for other frags that didn't occupy the whole 
page. Since we pin the whole user page, better to count the whole page 
size to prevent evil application.
> Thanks
> Shirley
>
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