Date: Mon, 24 Nov 2014 09:55:27 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: David Miller <davem@davemloft.net>, pagupta@redhat.com,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        dgibson@redhat.com, vfalico@gmail.com, edumazet@google.com,
        vyasevic@redhat.com, hkchu@google.com, wuzhy@linux.vnet.ibm.com,
        xemul@parallels.com, therbert@google.com, bhutchings@solarflare.com,
        xii@google.com, stephen@networkplumber.org, jiri@resnulli.us,
        sergei.shtylyov@cogentembedded.com
Subject: Re: [PATCH net-net 0/4] Increase the limit of tuntap queues
Message-ID: <20141124075527.GC6286@redhat.com>
References: <1416327778-17716-1-git-send-email-pagupta@redhat.com>
 <20141119.151628.768548269128919029.davem@davemloft.net>
 <20141119204427.GB30994@redhat.com>
 <20141123104623.GA31915@redhat.com>
 <5472A499.60906@redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org

On Mon, Nov 24, 2014 at 11:23:05AM +0800, Jason Wang wrote:
> On 11/23/2014 06:46 PM, Michael S. Tsirkin wrote:
> > On Wed, Nov 19, 2014 at 10:44:27PM +0200, Michael S. Tsirkin wrote:
> >> > On Wed, Nov 19, 2014 at 03:16:28PM -0500, David Miller wrote:
> >>> > > From: Pankaj Gupta <pagupta@redhat.com>
> >>> > > Date: Tue, 18 Nov 2014 21:52:54 +0530
> >>> > > 
> >>>> > > > - Accept maximum number of queues as sysctl param so that any user space 
> >>>> > > >   application like libvirt can use this value to limit number of queues. Also
> >>>> > > >   Administrators can specify maximum number of queues by updating this sysctl
> >>>> > > >   entry.
> >>> > > 
> >>> > > This is the only part I don't like.
> >>> > > 
> >>> > > Just let whoever has privileges to configure the tun device shoot
> >>> > > themselves in the foot if they want to by configuring "too many"
> >>> > > queues.
> >>> > > 
> >>> > > If the virtual entity runs itself out of resources by doing something
> >>> > > stupid, it's purely their problem.
> >> > 
> >> > Well it will run host out of kernel, no?
> > To clarify:
> >
> > At the moment attaching/detaching queues is an unpriveledged operation.
> >
> > Shouldn't we worry that an application can cause large
> > allocations, and provide a way to limit these?
> 
> But creating new queues (TUNSETIFF) is privileged. There's no way for
> unprivileged user to allocate more resources. So we are safe here?

Hmm, that's true, I think I was confused.
Thanks for setting me straight.

-- 
MST
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