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 10:28:07AM -0700, Stephen Hemminger wrote:
> On Wed, 30 Sep 2015 13:37:22 +0300
> Vlad Zolotarov <vladz@cloudius-systems.com> wrote:
> 
> > 
> > 
> > On 09/30/15 00:49, Michael S. Tsirkin wrote:
> > > On Tue, Sep 29, 2015 at 02:46:16PM -0700, Stephen Hemminger wrote:
> > >> On Tue, 29 Sep 2015 23:54:54 +0300
> > >> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >>
> > >>> On Tue, Sep 29, 2015 at 07:41:09PM +0300, Vlad Zolotarov wrote:
> > >>>> The security breach motivation u brought in "[RFC PATCH] uio:
> > >>>> uio_pci_generic: Add support for MSI interrupts" thread seems a bit weak
> > >>>> since one u let the userland access to the bar it may do any funny thing
> > >>>> using the DMA engine of the device. This kind of stuff should be prevented
> > >>>> using the iommu and if it's enabled then any funny tricks using MSI/MSI-X
> > >>>> configuration will be prevented too.
> > >>>>
> > >>>> I'm about to send the patch to main Linux mailing list. Let's continue this
> > >>>> discussion there.
> > >>>>    
> > >>> Basically UIO shouldn't be used with devices capable of DMA.
> > >>> Use VFIO for that (yes, this implies an emulated or PV IOMMU).
> > 
> > If there is an IOMMU in the picture there shouldn't be any problem to 
> > use UIO with DMA capable devices.
> > 
> > >>> I don't think this can change.
> > >> Given there is no PV IOMMU and even if there was it would be too slow for DPDK
> > >> use, I can't accept that.
> > > QEMU does allow emulating an iommu.
> > 
> > Amazon's EC2 xen HV doesn't. At least today. Therefore VFIO is not an 
> > option there. And again, it's a general issue not DPDK specific.
> > Today one has to develop some proprietary modules (like igb_uio) to 
> > workaround the issue and this is lame. IMHO uio_pci_generic should
> > be fixed to be able to properly work within any virtualized environment 
> > and not only with KVM.
> > 
> 
> Also VMware (bigger problem) has no IOMMU emulation.
> Other environments as well (Windriver, GCE) have noe IOMMU.

Because the use-case of userspace drivers is not important enough?
Without an IOMMU, there's no way to have secure userspace drivers.

-- 
MST