linux-kernel - Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host kernel

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Message-ID: <20100915173034.GB2612@redhat.com>
Date:	Wed, 15 Sep 2010 19:30:34 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Avi Kivity <avi@...hat.com>,
	"Xin, Xiaohui" <xiaohui.xin@...el.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] macvtap: TX zero copy between guest and host
 kernel

On Wed, Sep 15, 2010 at 10:00:04AM -0700, Shirley Ma wrote:
> On Wed, 2010-09-15 at 17:39 +0200, Michael S. Tsirkin wrote:
> > In fact, I rechecked: both bridge and loopback have NETIF_F_HIGHDMA
> > set.
> > So maybe we should check NETIF_F_NETNS_LOCAL ...
> > 
> > macvtap in bridged mode is interesting as well. 
> 
> I found that too, just wondered which flag to use is better. :)
> 
> Thanks
> Shirley

At some level NETIF_F_NETNS_LOCAL makes sense: local packets
can get anywhere. OTOH one wonders whether there might be other
issues, e.g. in theory devices could hang on to frag pages
just by doing get_page.  There might be other issues.
Maybe we are better off white-listing known-good drivers
with a new flag?

-- 
MST
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