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Re: [Qemu-devel] snabbswitch integration with QEMU for userspace etherne
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O |
Date: |
Wed, 29 May 2013 09:49:29 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, May 28, 2013 at 08:17:42PM +0300, Michael S. Tsirkin wrote:
> On Tue, May 28, 2013 at 12:00:38PM -0500, Anthony Liguori wrote:
> > Julian Stecklina <address@hidden> writes:
> >
> > > On 05/28/2013 12:10 PM, Luke Gorrie wrote:
> > >> On 27 May 2013 11:34, Stefan Hajnoczi <address@hidden
> > >> <mailto:address@hidden>> wrote:
> > >>
> > >> vhost_net is about connecting the a virtio-net speaking process to a
> > >> tun-like device. The problem you are trying to solve is connecting a
> > >> virtio-net speaking process to Snabb Switch.
> > >>
> > >>
> > >> Yep!
> > >
> > > Since I am on a similar path as Luke, let me share another idea.
> > >
> > > What about extending qemu in a way to allow PCI device models to be
> > > implemented in another process.
> >
> > We aren't going to support any interface that enables out of tree
> > devices. This is just plugins in a different form with even more
> > downsides. You cannot easily keep track of dirty info, the guest
> > physical address translation to host is difficult to keep in sync
> > (imagine the complexity of memory hotplug).
> >
> > Basically, it's easy to hack up but extremely hard to do something that
> > works correctly overall.
> >
> > There isn't a compelling reason to implement something like this other
> > than avoiding getting code into QEMU. Best to just submit your device
> > to QEMU for inclusion.
> >
> > If you want to avoid copying in a vswitch, better to use something like
> > vmsplice as I outlined in another thread.
> >
> > > This is not as hard as it may sound.
> > > qemu would open a domain socket to this process and map VM memory over
> > > to the other side. This can be accomplished by having file descriptors
> > > in qemu to VM memory (reusing -mem-path code) and passing those over the
> > > domain socket. The other side can then just mmap them. The socket would
> > > also be used for configuration and I/O by the guest on the PCI
> > > I/O/memory regions. You could also use this to do IRQs or use eventfds,
> > > whatever works better.
> > >
> > > To have a zero copy userspace switch, the switch would offer virtio-net
> > > devices to any qemu that wants to connect to it and implement the
> > > complete device logic itself. Since it has access to all guest memory,
> > > it can just do memcpy for packet data. Of course, this only works for
> > > 64-bit systems, because you need vast amounts of virtual address space.
> > > In my experience, doing this in userspace is _way less painful_.
> > >
> > > If you can get away with polling in the switch the overhead of doing all
> > > this in userspace is zero. And as long as you can rate-limit explicit
> > > notifications over the socket even that overhead should be okay.
> > >
> > > Opinions?
> >
> > I don't see any compelling reason to do something like this. It's
> > jumping through a tremendous number of hoops to avoid putting code that
> > belongs in QEMU in tree.
> >
> > Regards,
> >
> > Anthony Liguori
> >
> > >
> > > Julian
>
> OTOH an in-tree device that runs in a separate process would
> be useful e.g. for security.
> For example, we could limit a virtio-net device process
> to only access tap and vhost files.
For tap or vhost files only this is good for security. I'm not sure it
has many advantages over a QEMU process under SELinux though.
Obviously when the switch process has shared memory access to multiple
guests' RAM, the security is worse than a QEMU process solution but
better than a vhost kernel solution.
So the security story is not a clear win.
Stefan
- Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O, (continued)
- Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O, Luke Gorrie, 2013/05/28
- Re: [Qemu-devel] [snabb-devel:276] Re: snabbswitch integration with QEMU for userspace ethernet I/O, Julian Stecklina, 2013/05/28
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Anthony Liguori, 2013/05/28
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Michael S. Tsirkin, 2013/05/28
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Anthony Liguori, 2013/05/28
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Stefano Stabellini, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Michael S. Tsirkin, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Stefano Stabellini, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O,
Stefan Hajnoczi <=
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Michael S. Tsirkin, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Stefan Hajnoczi, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Michael S. Tsirkin, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Julian Stecklina, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, ronnie sahlberg, 2013/05/29
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Stefan Hajnoczi, 2013/05/30
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Michael S. Tsirkin, 2013/05/30
- Re: [Qemu-devel] [snabb-devel:308] Re: snabbswitch integration with QEMU for userspace ethernet I/O, Luke Gorrie, 2013/05/30
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Julian Stecklina, 2013/05/30
- Re: [Qemu-devel] snabbswitch integration with QEMU for userspace ethernet I/O, Julian Stecklina, 2013/05/29