netdev - Re: [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable when performing the upcall

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 10 Jun 2013 13:34:23 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>,
	"dev@...nvswitch.org" <dev@...nvswitch.org>
Subject: Re: [PATCH net-next 2/2] openvswitch: Use zerocopy if applicable when
 performing the upcall

On Fri, Jun 7, 2013 at 5:21 AM, Thomas Graf <tgraf@...g.ch> wrote:
> On 05/27/13 at 10:28am, Jesse Gross wrote:
>> On Saturday, May 25, 2013, Eric Dumazet wrote:
>>
>> > On Sat, 2013-05-25 at 08:02 +0100, Thomas Graf wrote:
>> >
>> > > I ran TCP_CRR to verify the SYN/ACK use case and I did not
>> > > observe a difference. If you have any specific test in mind
>> > > I will be glad to run that before posting the 2nd revision.
>> >
>> > I guess you should test with rx checksum disabled as well, Jesse seemed
>> > to be concerned about that.
>>
>>
>>  I was actually thinking about the transmit side - rx checksum verification
>> doesn't matter much here since the result will get thrown away. However, if
>> the packet is CHECKSUM_PARTIAL then the checksum will have to get filled in
>> first and that's the code path that is a little different now.
>
> Do we actually need to complete the checksum before doing the
> upcall and if so, why? Couldn't the slow path do that if needed?
> The only reason I can think of where it would matter is if a
> controller injects the packet into another network stack such
> as RouteFlow.

Well, this is the slow path. I don't want to force userspace to deal
with this because it's an internal kernel optimization that is
platform-specific and requires carrying additional metadata around.

It's also very common for a packet to traverse another network stack -
it's typically a VM's.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html