Re: [dpdk-dev] Having troubles binding an SR-IOV VF to uio_pci_generic on Amazon instance

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 30, 2015 at 04:05:40PM +0300, Avi Kivity wrote:
> 
> 
> On 09/30/2015 03:27 PM, Michael S. Tsirkin wrote:
> >On Wed, Sep 30, 2015 at 03:16:04PM +0300, Vlad Zolotarov wrote:
> >>
> >>On 09/30/15 15:03, Michael S. Tsirkin wrote:
> >>>On Wed, Sep 30, 2015 at 02:53:19PM +0300, Vlad Zolotarov wrote:
> >>>>On 09/30/15 14:41, Michael S. Tsirkin wrote:
> >>>>>On Wed, Sep 30, 2015 at 02:26:01PM +0300, Vlad Zolotarov wrote:
> >>>>>>The whole idea is to bypass kernel. Especially for networking...
> >>>>>... on dumb hardware that doesn't support doing that securely.
> >>>>On a very capable HW that supports whatever security requirements needed
> >>>>(e.g. 82599 Intel's SR-IOV VF devices).
> >>>Network card type is irrelevant as long as you do not have an IOMMU,
> >>>otherwise you would just use e.g. VFIO.
> >>Sorry, but I don't follow your logic here - Amazon EC2 environment is a
> >>example where there *is* iommu but it's not virtualized
> >>and thus VFIO is
> >>useless and there is an option to use directly assigned SR-IOV networking
> >>device there where using the kernel drivers impose a performance impact
> >>compared to user space UIO-based user space kernel bypass mode of usage. How
> >>is it irrelevant? Could u, pls, clarify your point?
> >>
> >So it's not even dumb hardware, it's another piece of software
> >that forces an "all or nothing" approach where either
> >device has access to all VM memory, or none.
> >And this, unfortunately, leaves you with no secure way to
> >allow userspace drivers.
> 
> Some setups don't need security (they are single-user, single application).
> But do need a lot of performance (like 5X-10X performance).  An example is
> OpenVSwitch, security doesn't help it at all and if you force it to use the
> kernel drivers you cripple it.

We'd have to see there are actual users that need this.  So far, dpdk
seems like the only one, and it wants to use UIO for slow path stuff
like polling link status.  Why this needs kernel bypass support, I don't
know.  I asked, and got no answer.

> 
> Also, I'm root.  I can do anything I like, including loading a patched
> pci_uio_generic.  You're not providing _any_ security, you're simply making
> life harder for users.

Maybe that's true on your system. But I guess you know that's not true
for everyone, not in 2015.

> >So it makes even less sense to add insecure work-arounds in the kernel.
> >It seems quite likely that by the time the new kernel reaches
> >production X years from now, EC2 will have a virtual iommu.
> 
> I can adopt a new kernel tomorrow.  I have no influence on EC2.
> 
>

Xen grant tables sound like they could be the right interface
for EC2.  google search for "grant tables iommu" immediately gives me:
http://lists.xenproject.org/archives/html/xen-devel/2014-04/msg00963.html
Maybe latest Xen is already doing the right thing, and it's just the
question of making VFIO use that.

-- 
MST