netdev - Re: [RFC] [PATCH v2 3/3] Let host NIC driver to DMA to guest user space.

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Message-ID: <20100408175225.7577af19@nehalam>
Date:	Thu, 8 Apr 2010 17:52:25 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	"Xin, Xiaohui" <xiaohui.xin@...el.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>, "mst@...hat.com" <mst@...hat.com>,
	"jdike@...user-mode-linux.org" <jdike@...user-mode-linux.org>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [RFC] [PATCH v2 3/3] Let host NIC driver to DMA to guest user
 space.

On Tue, 6 Apr 2010 14:26:29 +0800
"Xin, Xiaohui" <xiaohui.xin@...el.com> wrote:

> >How do you deal with the DoS problem of hostile user space app posting huge
> >number of receives and never getting anything.   
> 
> That's a problem we are trying to deal with. It's critical for long term.
> Currently, we tried to limit the pages it can pin, but not sure how much is reasonable.
> For now, the buffers submitted is from guest virtio-net driver, so it's safe in some extent
> just for now.

It is critical even now. Once you get past toy benchmarks you will see things like
Java processes with 1000 threads all reading at once. 
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