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

[Vlad Zolotarov]

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 at 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.



>   DPDK uses static mappings, so I
> doubt it's speed matters at all.
>
> Anyway, DPDK is doing polling all the time. I don't see why does it
> insist on using interrupts to detect link up events. Just poll for that
> too.
>