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

[Peter Xu]

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...  Are you sure the MMIO traps are
setup correctly?  Can the VF do IO properly even without L2?

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.

> > 
> > -----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