Re: [Qemu-devel] QEMU and vIOMMU support for emulated VF passthrough to nested (L2) VM

[Peter Xu]

On Wed, Mar 27, 2019 at 08:57:56AM +0100, Knut Omang wrote:
> On Wed, 2019-03-27 at 14:41 +0800, Peter Xu wrote:
> > On Tue, Mar 26, 2019 at 01:23:12PM +0000, Elijah Shakkour wrote:
> > > Adding QEMU-devel
> > 
> > Hi, Elijah,
> > 
> > > 
> > > -----Original Message-----
> > > From: Michael S. Tsirkin <address@hidden> 
> > > Sent: Tuesday, March 26, 2019 2:53 PM
> > > To: Elijah Shakkour <address@hidden>
> > > Cc: Knut Omang <address@hidden>; Alex Williamson <address@hidden>;
> > Marcel Apfelbaum <address@hidden>; Stefan Hajnoczi <address@hidden>; 
> > address@hidden
> > > Subject: Re: QEMU and vIOMMU support for emulated VF passthrough to 
> > > nested (L2) VM
> > > 
> > > I think you forgot to copy the qemu mailing list.
> > > 
> > > On Tue, Mar 26, 2019 at 10:08:17AM +0000, Elijah Shakkour wrote:
> > > > My questions are:
> > > > 
> > > > - Suppose that there is an emulated NIC that supports SRIOV (I 
> > > > implemented such a
> > NIC), now does QEMU support a scenario of an emulated NIC that supports 
> > SRIOV in Hyper-V 
> > L1 guest, that invokes VF and pass it to nested linux L2 guest?
> > 
> > I am not an expert of SR-IOV but I can't see a limitation to not allow
> > that to happen.
> > 
> > > > - I'm using vIOMMU in L1, so what is needed to be done in QEMU or maybe 
> > > > in emulated
> > NIC PF/VF to allow DMA remapping and INT remapping work as expected?
> > 
> > Your below command line should work, and even it seems to be an
> > overkill.
> > 
> > If your device is completely emulated, IIUC you only simply need this
> > on the latest QEMU:
> > 
> >   -M q35 -device intel-iommu
> > 
> > Split-irqchip and IR is on by default now, so you'll naturally gain
> > x2apic if it's supported.  You can use x-aw-bits but only if you
> > really need address space beyond 39 bits (which I suspect).  The rest
> > parameters are optional too.
> > 
> > > > - Does the command line below -that I use to run QEMU- seem ok for the 
> > > > scenario I
> > described to work?
> > 
> > Before I look into details of the cmdline - I'd say MMIO in L2 should
> > have nothing to do with IOMMU...  
> 
> The addresses used in L2 is the GPAs of the L2, which would typically be 
> different from
> the L2 HPAs == L1 GPAs, so I think the IOMMU mappings must work.
> 
> You would need something like 'intel_iommu=on iommu=pt' as boot parameters 
> for L1.

Yes, the IOMMU must work to do the assignment.  What I meant was that
IOMMU should not be in the code path of MMIO accesses even for L2.
IIUC that's the processor who reads/writes to the memory region and if
it's a MMIO issue then it probably has little to do with IOMMU.

Thanks,

> 
> > Are you sure the MMIO traps are
> > setup correctly?  Can the VF do IO properly even without L2?
> 
> I agree with Peter that just running the VF as another function in L1 
> would be good to test before trying to get L2 passthrough to work.
> 
> I recommend you also verify that passing the PF through works as expected, 
> unless you already have done so.
> 
> And do you see correct BAR address values in the lspci -vvv output in the L2 
> instance?
> 
> The SR/IOV logic is from QEMU's perspective just another device instance 
> apart from the differences in the BAR setup code, so if passing through a 
> non-virtual device works, and VF BAR addresses appear right, 
> I believe VFs should work as well.
> 
> > Also I don't know whether there can be some tricks when you boot L2
> > with vfio-pci when the device to assign is a VF.
> 
> A lot has happened since I was actively using the SR/IOV patch set myself so 
> that might entirely be possible from my perspective.
> 
> Thanks,
> Knut 
> 
> > > > 
> > > > -----Original Message-----
> > > > From: Michael S. Tsirkin <address@hidden>
> > > > Sent: Monday, March 25, 2019 4:14 AM
> > > > To: Elijah Shakkour <address@hidden>
> > > > Cc: Knut Omang <address@hidden>; Alex Williamson 
> > > > <address@hidden>; Marcel Apfelbaum 
> > > > <address@hidden>; Stefan Hajnoczi <address@hidden>
> > > > Subject: Re: QEMU and vIOMMU support for emulated VF passthrough to 
> > > > nested (L2) VM
> > > > 
> > > > Pls post all questions on list.
> > > > I have a policy against answering off-list mail.
> > > > Cc Pter Xu might be a good idea, too.
> > > > 
> > > > On Sun, Mar 24, 2019 at 09:56:26PM +0000, Elijah Shakkour wrote:
> > > > > Hey,
> > > > > 
> > > > > I'm emulating Mellanox ConnectX-4 in QEMU and right now, I'm adding 
> > > > > SRIOV
> > capability.
> > > > > I'm using Knut Omang SRIOV patches rebased to QEMU v2.12.
> > > > > My server (L0) is Linux. L1 guest is Windows2016 Hyper-V and L2 guest 
> > > > > is Linux
> > RH7.2.
> > > > > I can see my device in L1 VM and I see the invocation of the VF via 
> > > > > SRIOV
> > capability.
> > > > > Inside L2 guest I see the virtual function in "lspci' command.
> > > > > But when driver of L2 guest issues MMIO read/write, my MMIO ops don't 
> > > > > get called.
> > > > > I implemented my VF basically like Omang SRIOV example patch.
> > > > > 
> > > > > Could you please shed some light on what you think I might be missing?
> > > > > 
> > > > > Here is the command line I run:
> > > > > 
> > > > > ./x86_64-softmmu/qemu-system-x86_64 \  -machine 
> > > > > q35,accel=kvm,usb=off,dump-guest-core=off,kernel-irqchip=split \  -m 
> > > > > 32G \  -smp 2 \  -enable-kvm \  -cpu 
> > > > > host,vmx=on,ss=on,cx16=on,x2apic=on,hypervisor=on,lahf_lm=on,hv_time
> > > > > ,h v_relaxed,hv_vapic,hv_spinlocks=0x1fff,kvm=on \  -vnc 
> > > > > 127.0.0.1:0,to=99,id=default \  -drive
> > > > > file=$IMAGE,format=qcow2,if=none,id=drive-sata0-0-0 \  -chardev
> > > > > pty,id=charserial0 \  -device
> > > > > intel-iommu,intremap=on,caching-mode=on,device-iotlb=on,eim=on,x-aw-
> > > > > bi
> > > > > ts=48 \  -device
> > > > > ide-hd,bus=ide.0,drive=drive-sata0-0-0,id=sata0-0-0,bootindex=0 \ 
> > > > > -device 
> > > > > pcie-root-port,pref64-reserve=500M,slot=0,id=pcie_port.1,bus=pcie.0,
> > > > > mu
> > > > > ltifunction=on \  -netdev
> > > > > tap,id=tap5,ifname=tap5,script=no,downscript=no \  -device 
> > > > > connectx4,netdev=tap5,bus=pcie_port.1,multifunction=on
> > 
> > Regards,
> > 
> 

-- 
Peter Xu