Re: [Qemu-devel] Question: SRIOV support over Win Hyper-V VM running in QEMU process on Linux host

[Alex Williamson]

On Thu, 26 Jul 2018 20:11:44 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Thu, Jul 26, 2018 at 10:42:52AM -0600, Alex Williamson wrote:
> > On Thu, 26 Jul 2018 19:14:45 +0300
> > "Michael S. Tsirkin" <address@hidden> wrote:
> >   
> > > On Thu, Jul 26, 2018 at 06:51:13PM +0300, Marcel Apfelbaum wrote:  
> > > > Hi
> > > > 
> > > > On 07/26/2018 05:52 PM, Stefan Hajnoczi wrote:    
> > > > > On Thu, Jul 12, 2018 at 07:33:14AM +0000, Elijah Shakkour wrote:    
> > > > > > Hey,
> > > > > > 
> > > > > > Our team is adding a NIC functional  emulation to QEMU.
> > > > > > One of the features we are adding to this NIC is SRIOV.
> > > > > > 
> > > > > > Here is the error message I get when checking SRIOV support of  our 
> > > > > > emulated NIC on Win2016 server (the hyper-v VM).
> > > > > > "
> > > > > > SR-IOV cannot be used on this system as the PCI Express hardware 
> > > > > > does not support Access Control Services (ACS) at any root port.    
> > > > 
> > > > QEMU's emulated PCI Express Root Ports do not support ACS yet, however 
> > > > I am
> > > > not sure ACS is a prerequisite
> > > > for SR-IOV.  
> > 
> > ACS is certainly not a prerequisite for SR-IOV.
> >    
> > > Looks like windows blocks dev assignment in nested VMs without it.
> > > Thinking about it, doesn't vfio do the same by default? I think vfio has
> > > a flag to override this though.  
> > 
> > IOMMU grouping in Linux takes isolation via ACS and device specific
> > mechanisms into account, limiting the granularity with which a
> > userspace driver can claim ownership of devices,  
> 
> In that you must assign all devices behind this port as a group?

Yup.  Not very useful with SR-IOV.  Thanks,

Alex