On Fri, Jan 3, 2025 at 2:06 PM Sahil Siddiq <icegambi...@gmail.com> wrote:
>
> Hi,
>
> On 12/20/24 12:28 PM, Eugenio Perez Martin wrote:
> > On Thu, Dec 19, 2024 at 8:37 PM Sahil Siddiq <icegambi...@gmail.com> wrote:
> >>
> >> Hi,
> >>
> >> On 12/17/24 1:20 PM, Eugenio Perez Martin wrote:
> >>> On Tue, Dec 17, 2024 at 6:45 AM Sahil Siddiq <icegambi...@gmail.com>
> >>> wrote:
> >>>> On 12/16/24 2:09 PM, Eugenio Perez Martin wrote:
> >>>>> On Sun, Dec 15, 2024 at 6:27 PM Sahil Siddiq <icegambi...@gmail.com>
> >>>>> wrote:
> >>>>>> On 12/10/24 2:57 PM, Eugenio Perez Martin wrote:
> >>>>>>> On Thu, Dec 5, 2024 at 9:34 PM Sahil Siddiq <icegambi...@gmail.com>
> >>>>>>> wrote:
> >>>>>>>> [...]
> >>>>>>>> I have been following the "Hands on vDPA: what do you do
> >>>>>>>> when you ain't got the hardware v2 (Part 2)" [1] blog to
> >>>>>>>> test my changes. To boot the L1 VM, I ran:
> >>>>>>>>
> >>>>>>>> sudo ./qemu/build/qemu-system-x86_64 \
> >>>>>>>> -enable-kvm \
> >>>>>>>> -drive
> >>>>>>>> file=//home/valdaarhun/valdaarhun/qcow2_img/L1.qcow2,media=disk,if=virtio
> >>>>>>>> \
> >>>>>>>> -net nic,model=virtio \
> >>>>>>>> -net user,hostfwd=tcp::2222-:22 \
> >>>>>>>> -device intel-iommu,snoop-control=on \
> >>>>>>>> -device
> >>>>>>>> virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off,iommu_platform=on,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,packed=on,event_idx=off,bus=pcie.0,addr=0x4
> >>>>>>>> \
> >>>>>>>> -netdev tap,id=net0,script=no,downscript=no \
> >>>>>>>> -nographic \
> >>>>>>>> -m 8G \
> >>>>>>>> -smp 4 \
> >>>>>>>> -M q35 \
> >>>>>>>> -cpu host 2>&1 | tee vm.log
> >>>>>>>>
> >>>>>>>> Without "guest_uso4=off,guest_uso6=off,host_uso=off,
> >>>>>>>> guest_announce=off" in "-device virtio-net-pci", QEMU
> >>>>>>>> throws "vdpa svq does not work with features" [2] when
> >>>>>>>> trying to boot L2.
> >>>>>>>>
> >>>>>>>> The enums added in commit #2 in this series is new and
> >>>>>>>> wasn't in the earlier versions of the series. Without
> >>>>>>>> this change, x-svq=true throws "SVQ invalid device feature
> >>>>>>>> flags" [3] and x-svq is consequently disabled.
> >>>>>>>>
> >>>>>>>> The first issue is related to running traffic in L2
> >>>>>>>> with vhost-vdpa.
> >>>>>>>>
> >>>>>>>> In L0:
> >>>>>>>>
> >>>>>>>> $ ip addr add 111.1.1.1/24 dev tap0
> >>>>>>>> $ ip link set tap0 up
> >>>>>>>> $ ip addr show tap0
> >>>>>>>> 4: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
> >>>>>>>> state UNKNOWN group default qlen 1000
> >>>>>>>> link/ether d2:6d:b9:61:e1:9a brd ff:ff:ff:ff:ff:ff
> >>>>>>>> inet 111.1.1.1/24 scope global tap0
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>> inet6 fe80::d06d:b9ff:fe61:e19a/64 scope link proto kernel_ll
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>>
> >>>>>>>> I am able to run traffic in L2 when booting without
> >>>>>>>> x-svq.
> >>>>>>>>
> >>>>>>>> In L1:
> >>>>>>>>
> >>>>>>>> $ ./qemu/build/qemu-system-x86_64 \
> >>>>>>>> -nographic \
> >>>>>>>> -m 4G \
> >>>>>>>> -enable-kvm \
> >>>>>>>> -M q35 \
> >>>>>>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \
> >>>>>>>> -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0 \
> >>>>>>>> -device
> >>>>>>>> virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7
> >>>>>>>> \
> >>>>>>>> -smp 4 \
> >>>>>>>> -cpu host \
> >>>>>>>> 2>&1 | tee vm.log
> >>>>>>>>
> >>>>>>>> In L2:
> >>>>>>>>
> >>>>>>>> # ip addr add 111.1.1.2/24 dev eth0
> >>>>>>>> # ip addr show eth0
> >>>>>>>> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
> >>>>>>>> state UP group default qlen 1000
> >>>>>>>> link/ether 52:54:00:12:34:57 brd ff:ff:ff:ff:ff:ff
> >>>>>>>> altname enp0s7
> >>>>>>>> inet 111.1.1.2/24 scope global eth0
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>> inet6 fe80::9877:de30:5f17:35f9/64 scope link noprefixroute
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>>
> >>>>>>>> # ip route
> >>>>>>>> 111.1.1.0/24 dev eth0 proto kernel scope link src 111.1.1.2
> >>>>>>>>
> >>>>>>>> # ping 111.1.1.1 -w3
> >>>>>>>> PING 111.1.1.1 (111.1.1.1) 56(84) bytes of data.
> >>>>>>>> 64 bytes from 111.1.1.1: icmp_seq=1 ttl=64 time=0.407 ms
> >>>>>>>> 64 bytes from 111.1.1.1: icmp_seq=2 ttl=64 time=0.671 ms
> >>>>>>>> 64 bytes from 111.1.1.1: icmp_seq=3 ttl=64 time=0.291 ms
> >>>>>>>>
> >>>>>>>> --- 111.1.1.1 ping statistics ---
> >>>>>>>> 3 packets transmitted, 3 received, 0% packet loss, time 2034ms
> >>>>>>>> rtt min/avg/max/mdev = 0.291/0.456/0.671/0.159 ms
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> But if I boot L2 with x-svq=true as shown below, I am unable
> >>>>>>>> to ping the host machine.
> >>>>>>>>
> >>>>>>>> $ ./qemu/build/qemu-system-x86_64 \
> >>>>>>>> -nographic \
> >>>>>>>> -m 4G \
> >>>>>>>> -enable-kvm \
> >>>>>>>> -M q35 \
> >>>>>>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \
> >>>>>>>> -netdev
> >>>>>>>> type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,x-svq=true,id=vhost-vdpa0
> >>>>>>>> \
> >>>>>>>> -device
> >>>>>>>> virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7
> >>>>>>>> \
> >>>>>>>> -smp 4 \
> >>>>>>>> -cpu host \
> >>>>>>>> 2>&1 | tee vm.log
> >>>>>>>>
> >>>>>>>> In L2:
> >>>>>>>>
> >>>>>>>> # ip addr add 111.1.1.2/24 dev eth0
> >>>>>>>> # ip addr show eth0
> >>>>>>>> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel
> >>>>>>>> state UP group default qlen 1000
> >>>>>>>> link/ether 52:54:00:12:34:57 brd ff:ff:ff:ff:ff:ff
> >>>>>>>> altname enp0s7
> >>>>>>>> inet 111.1.1.2/24 scope global eth0
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>> inet6 fe80::9877:de30:5f17:35f9/64 scope link noprefixroute
> >>>>>>>> valid_lft forever preferred_lft forever
> >>>>>>>>
> >>>>>>>> # ip route
> >>>>>>>> 111.1.1.0/24 dev eth0 proto kernel scope link src 111.1.1.2
> >>>>>>>>
> >>>>>>>> # ping 111.1.1.1 -w10
> >>>>>>>> PING 111.1.1.1 (111.1.1.1) 56(84) bytes of data.
> >>>>>>>> From 111.1.1.2 icmp_seq=1 Destination Host Unreachable
> >>>>>>>> ping: sendmsg: No route to host
> >>>>>>>> From 111.1.1.2 icmp_seq=2 Destination Host Unreachable
> >>>>>>>> From 111.1.1.2 icmp_seq=3 Destination Host Unreachable
> >>>>>>>>
> >>>>>>>> --- 111.1.1.1 ping statistics ---
> >>>>>>>> 3 packets transmitted, 0 received, +3 errors, 100% packet loss, time
> >>>>>>>> 2076ms
> >>>>>>>> pipe 3
> >>>>>>>>
> >>>>>>>> The other issue is related to booting L2 with "x-svq=true"
> >>>>>>>> and "packed=on".
> >>>>>>>>
> >>>>>>>> In L1:
> >>>>>>>>
> >>>>>>>> $ ./qemu/build/qemu-system-x86_64 \
> >>>>>>>> -nographic \
> >>>>>>>> -m 4G \
> >>>>>>>> -enable-kvm \
> >>>>>>>> -M q35 \
> >>>>>>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \
> >>>>>>>> -netdev
> >>>>>>>> type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=true
> >>>>>>>> \
> >>>>>>>> -device
> >>>>>>>> virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,packed=on,bus=pcie.0,addr=0x7
> >>>>>>>> \
> >>>>>>>> -smp 4 \
> >>>>>>>> -cpu host \
> >>>>>>>> 2>&1 | tee vm.log
> >>>>>>>>
> >>>>>>>> The kernel throws "virtio_net virtio1: output.0:id 0 is not
> >>>>>>>> a head!" [4].
> >>>>>>>>
> >>>>>>>
> >>>>>>> So this series implements the descriptor forwarding from the guest to
> >>>>>>> the device in packed vq. We also need to forward the descriptors from
> >>>>>>> the device to the guest. The device writes them in the SVQ ring.
> >>>>>>>
> >>>>>>> The functions responsible for that in QEMU are
> >>>>>>> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_flush, which is called by
> >>>>>>> the device when used descriptors are written to the SVQ, which calls
> >>>>>>> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_get_buf. We need to do
> >>>>>>> modifications similar to vhost_svq_add: Make them conditional if we're
> >>>>>>> in split or packed vq, and "copy" the code from Linux's
> >>>>>>> drivers/virtio/virtio_ring.c:virtqueue_get_buf.
> >>>>>>>
> >>>>>>> After these modifications you should be able to ping and forward
> >>>>>>> traffic. As always, It is totally ok if it needs more than one
> >>>>>>> iteration, and feel free to ask any question you have :).
> >>>>>>>
> >>>>>>
> >>>>>> I misunderstood this part. While working on extending
> >>>>>> hw/virtio/vhost-shadow-virtqueue.c:vhost_svq_get_buf() [1]
> >>>>>> for packed vqs, I realized that this function and
> >>>>>> vhost_svq_flush() already support split vqs. However, I am
> >>>>>> unable to ping L0 when booting L2 with "x-svq=true" and
> >>>>>> "packed=off" or when the "packed" option is not specified
> >>>>>> in QEMU's command line.
> >>>>>>
> >>>>>> I tried debugging these functions for split vqs after running
> >>>>>> the following QEMU commands while following the blog [2].
> >>>>>>
> >>>>>> Booting L1:
> >>>>>>
> >>>>>> $ sudo ./qemu/build/qemu-system-x86_64 \
> >>>>>> -enable-kvm \
> >>>>>> -drive
> >>>>>> file=//home/valdaarhun/valdaarhun/qcow2_img/L1.qcow2,media=disk,if=virtio
> >>>>>> \
> >>>>>> -net nic,model=virtio \
> >>>>>> -net user,hostfwd=tcp::2222-:22 \
> >>>>>> -device intel-iommu,snoop-control=on \
> >>>>>> -device
> >>>>>> virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off,iommu_platform=on,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,ctrl_vq=on,ctrl_rx=on,packed=off,event_idx=off,bus=pcie.0,addr=0x4
> >>>>>> \
> >>>>>> -netdev tap,id=net0,script=no,downscript=no \
> >>>>>> -nographic \
> >>>>>> -m 8G \
> >>>>>> -smp 4 \
> >>>>>> -M q35 \
> >>>>>> -cpu host 2>&1 | tee vm.log
> >>>>>>
> >>>>>> Booting L2:
> >>>>>>
> >>>>>> # ./qemu/build/qemu-system-x86_64 \
> >>>>>> -nographic \
> >>>>>> -m 4G \
> >>>>>> -enable-kvm \
> >>>>>> -M q35 \
> >>>>>> -drive file=//root/L2.qcow2,media=disk,if=virtio \
> >>>>>> -netdev
> >>>>>> type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,x-svq=true,id=vhost-vdpa0 \
> >>>>>> -device
> >>>>>> virtio-net-pci,netdev=vhost-vdpa0,disable-legacy=on,disable-modern=off,ctrl_vq=on,ctrl_rx=on,event_idx=off,bus=pcie.0,addr=0x7
> >>>>>> \
> >>>>>> -smp 4 \
> >>>>>> -cpu host \
> >>>>>> 2>&1 | tee vm.log
> >>>>>>
> >>>>>> I printed out the contents of VirtQueueElement returned
> >>>>>> by vhost_svq_get_buf() in vhost_svq_flush() [3].
> >>>>>> I noticed that "len" which is set by "vhost_svq_get_buf"
> >>>>>> is always set to 0 while VirtQueueElement.len is non-zero.
> >>>>>> I haven't understood the difference between these two "len"s.
> >>>>>>
> >>>>>
> >>>>> VirtQueueElement.len is the length of the buffer, while the len of
> >>>>> vhost_svq_get_buf is the bytes written by the device. In the case of
> >>>>> the tx queue, VirtQueuelen is the length of the tx packet, and the
> >>>>> vhost_svq_get_buf is always 0 as the device does not write. In the
> >>>>> case of rx, VirtQueueElem.len is the available length for a rx frame,
> >>>>> and the vhost_svq_get_buf len is the actual length written by the
> >>>>> device.
> >>>>>
> >>>>> To be 100% accurate a rx packet can span over multiple buffers, but
> >>>>> SVQ does not need special code to handle this.
> >>>>>
> >>>>> So vhost_svq_get_buf should return > 0 for rx queue (svq->vq->index ==
> >>>>> 0), and 0 for tx queue (svq->vq->index % 2 == 1).
> >>>>>
> >>>>> Take into account that vhost_svq_get_buf only handles split vq at the
> >>>>> moment! It should be renamed or splitted into vhost_svq_get_buf_split.
> >>>>
> >>>> In L1, there are 2 virtio network devices.
> >>>>
> >>>> # lspci -nn | grep -i net
> >>>> 00:02.0 Ethernet controller [0200]: Red Hat, Inc. Virtio network device
> >>>> [1af4:1000]
> >>>> 00:04.0 Ethernet controller [0200]: Red Hat, Inc. Virtio 1.0 network
> >>>> device [1af4:1041] (rev 01)
> >>>>
> >>>> I am using the second one (1af4:1041) for testing my changes and have
> >>>> bound this device to the vp_vdpa driver.
> >>>>
> >>>> # vdpa dev show -jp
> >>>> {
> >>>> "dev": {
> >>>> "vdpa0": {
> >>>> "type": "network",
> >>>> "mgmtdev": "pci/0000:00:04.0",
> >>>> "vendor_id": 6900,
> >>>> "max_vqs": 3,
> >>>
> >>> How is max_vqs=3? For this to happen L0 QEMU should have
> >>> virtio-net-pci,...,queues=3 cmdline argument.
> >
> > Ouch! I totally misread it :(. Everything is correct, max_vqs should
> > be 3. I read it as the virtio_net queues, which means queue *pairs*,
> > as it includes rx and tx queue.
>
> Understood :)
>
> >>
> >> I am not sure why max_vqs is 3. I haven't set the value of queues to 3
> >> in the cmdline argument. Is max_vqs expected to have a default value
> >> other than 3?
> >>
> >> In the blog [1] as well, max_vqs is 3 even though there's no queues=3
> >> argument.
> >>
> >>> It's clear the guest is not using them, we can add mq=off
> >>> to simplify the scenario.
> >>
> >> The value of max_vqs is still 3 after adding mq=off. The whole
> >> command that I run to boot L0 is:
> >>
> >> $ sudo ./qemu/build/qemu-system-x86_64 \
> >> -enable-kvm \
> >> -drive
> >> file=//home/valdaarhun/valdaarhun/qcow2_img/L1.qcow2,media=disk,if=virtio \
> >> -net nic,model=virtio \
> >> -net user,hostfwd=tcp::2222-:22 \
> >> -device intel-iommu,snoop-control=on \
> >> -device
> >> virtio-net-pci,netdev=net0,disable-legacy=on,disable-modern=off,iommu_platform=on,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off,mq=off,ctrl_vq=on,ctrl_rx=on,packed=off,event_idx=off,bus=pcie.0,addr=0x4
> >> \
> >> -netdev tap,id=net0,script=no,downscript=no \
> >> -nographic \
> >> -m 8G \
> >> -smp 4 \
> >> -M q35 \
> >> -cpu host 2>&1 | tee vm.log
> >>
> >> Could it be that 2 of the 3 vqs are used for the dataplane and
> >> the third vq is the control vq?
> >>
> >>>> "max_vq_size": 256
> >>>> }
> >>>> }
> >>>> }
> >>>>
> >>>> The max number of vqs is 3 with the max size being 256.
> >>>>
> >>>> Since, there are 2 virtio net devices, vhost_vdpa_svqs_start [1]
> >>>> is called twice. For each of them. it calls vhost_svq_start [2]
> >>>> v->shadow_vqs->len number of times.
> >>>>
> >>>
> >>> Ok I understand this confusion, as the code is not intuitive :). Take
> >>> into account you can only have svq in vdpa devices, so both
> >>> vhost_vdpa_svqs_start are acting on the vdpa device.
> >>>
> >>> You are seeing two calls to vhost_vdpa_svqs_start because virtio (and
> >>> vdpa) devices are modelled internally as two devices in QEMU: One for
> >>> the dataplane vq, and other for the control vq. There are historical
> >>> reasons for this, but we use it in vdpa to always shadow the CVQ while
> >>> leaving dataplane passthrough if x-svq=off and the virtio & virtio-net
> >>> feature set is understood by SVQ.
> >>>
> >>> If you break at vhost_vdpa_svqs_start with gdb and go higher in the
> >>> stack you should reach vhost_net_start, that starts each vhost_net
> >>> device individually.
> >>>
> >>> To be 100% honest, each dataplain *queue pair* (rx+tx) is modelled
> >>> with a different vhost_net device in QEMU, but you don't need to take
> >>> that into account implementing the packed vq :).
> >>
> >> Got it, this makes sense now.
> >>
> >>>> Printing the values of dev->vdev->name, v->shadow_vqs->len and
> >>>> svq->vring.num in vhost_vdpa_svqs_start gives:
> >>>>
> >>>> name: virtio-net
> >>>> len: 2
> >>>> num: 256
> >>>> num: 256
> >>>
> >>> First QEMU's vhost_net device, the dataplane.
> >>>
> >>>> name: virtio-net
> >>>> len: 1
> >>>> num: 64
> >>>>
> >>>
> >>> Second QEMU's vhost_net device, the control virtqueue.
> >>
> >> Ok, if I understand this correctly, the control vq doesn't
> >> need separate queues for rx and tx.
> >>
> >
> > That's right. Since CVQ has one reply per command, the driver can just
> > send ro+rw descriptors to the device. In the case of RX, the device
> > needs a queue with only-writable descriptors, as neither the device or
> > the driver knows how many packets will arrive.
>
> Got it, this makes sense now.
>
> >>>> I am not sure how to match the above log lines to the
> >>>> right virtio-net device since the actual value of num
> >>>> can be less than "max_vq_size" in the output of "vdpa
> >>>> dev show".
> >>>>
> >>>
> >>> Yes, the device can set a different vq max per vq, and the driver can
> >>> negotiate a lower vq size per vq too.
> >>>
> >>>> I think the first 3 log lines correspond to the virtio
> >>>> net device that I am using for testing since it has
> >>>> 2 vqs (rx and tx) while the other virtio-net device
> >>>> only has one vq.
> >>>>
> >>>> When printing out the values of svq->vring.num,
> >>>> used_elem.len and used_elem.id in vhost_svq_get_buf,
> >>>> there are two sets of output. One set corresponds to
> >>>> svq->vring.num = 64 and the other corresponds to
> >>>> svq->vring.num = 256.
> >>>>
> >>>> For svq->vring.num = 64, only the following line
> >>>> is printed repeatedly:
> >>>>
> >>>> size: 64, len: 1, i: 0
> >>>>
> >>>
> >>> This is with packed=off, right? If this is testing with packed, you
> >>> need to change the code to accommodate it. Let me know if you need
> >>> more help with this.
> >>
> >> Yes, this is for packed=off. For the time being, I am trying to
> >> get L2 to communicate with L0 using split virtqueues and x-svq=true.
> >>
> >
> > Got it.
> >
> >>> In the CVQ the only reply is a byte, indicating if the command was
> >>> applied or not. This seems ok to me.
> >>
> >> Understood.
> >>
> >>> The queue can also recycle ids as long as they are not available, so
> >>> that part seems correct to me too.
> >>
> >> I am a little confused here. The ids are recycled when they are
> >> available (i.e., the id is not already in use), right?
> >>
> >
> > In virtio, available is that the device can use them. And used is that
> > the device returned to the driver. I think you're aligned it's just it
> > is better to follow the virtio nomenclature :).
>
> Got it.
>
> >>>> For svq->vring.num = 256, the following line is
> >>>> printed 20 times,
> >>>>
> >>>> size: 256, len: 0, i: 0
> >>>>
> >>>> followed by:
> >>>>
> >>>> size: 256, len: 0, i: 1
> >>>> size: 256, len: 0, i: 1
> >>>>
> >>>
> >>> This makes sense for the tx queue too. Can you print the VirtQueue index?
> >>
> >> For svq->vring.num = 64, the vq index is 2. So the following line
> >> (svq->vring.num, used_elem.len, used_elem.id, svq->vq->queue_index)
> >> is printed repeatedly:
> >>
> >> size: 64, len: 1, i: 0, vq idx: 2
> >>
> >> For svq->vring.num = 256, the following line is repeated several
> >> times:
> >>
> >> size: 256, len: 0, i: 0, vq idx: 1
> >>
> >> This is followed by:
> >>
> >> size: 256, len: 0, i: 1, vq idx: 1
> >>
> >> In both cases, queue_index is 1. To get the value of queue_index,
> >> I used "virtio_get_queue_index(svq->vq)" [2].
> >>
> >> Since the queue_index is 1, I guess this means this is the tx queue
> >> and the value of len (0) is correct. However, nothing with
> >> queue_index % 2 == 0 is printed by vhost_svq_get_buf() which means
> >> the device is not sending anything to the guest. Is this correct?
> >>
> >
> > Yes, that's totally correct.
> >
> > You can set -netdev tap,...,vhost=off in L0 qemu and trace (or debug
> > with gdb) it to check what is receiving. You should see calls to
> > hw/net/virtio-net.c:virtio_net_flush_tx. The corresponding function to
> > receive is virtio_net_receive_rcu, I recommend you trace too just it
> > in case you see any strange call to it.
> >
>
> I added "vhost=off" to -netdev tap in L0's qemu command. I followed all
> the steps in the blog [1] up till the point where L2 is booted. Before
> booting L2, I had no issues pinging L0 from L1.
>
> For each ping, the following trace lines were printed by QEMU:
>
> virtqueue_alloc_element elem 0x5d041024f560 size 56 in_num 0 out_num 1
> virtqueue_pop vq 0x5d04109b0ce8 elem 0x5d041024f560 in_num 0 out_num 1
> virtqueue_fill vq 0x5d04109b0ce8 elem 0x5d041024f560 len 0 idx 0
> virtqueue_flush vq 0x5d04109b0ce8 count 1
> virtio_notify vdev 0x5d04109a8d50 vq 0x5d04109b0ce8
> virtqueue_alloc_element elem 0x5d041024f560 size 56 in_num 1 out_num 0
> virtqueue_pop vq 0x5d04109b0c50 elem 0x5d041024f560 in_num 1 out_num 0
> virtqueue_fill vq 0x5d04109b0c50 elem 0x5d041024f560 len 110 idx 0
> virtqueue_flush vq 0x5d04109b0c50 count 1
> virtio_notify vdev 0x5d04109a8d50 vq 0x5d04109b0c50
>
> The first 5 lines look like they were printed when an echo request was
> sent to L0 and the next 5 lines were printed when an echo reply was
> received.
>
> After booting L2, I set up the tap device's IP address in L0 and the
> vDPA port's IP address in L2.
>
> When trying to ping L0 from L2, I only see the following lines being
> printed:
>
> virtqueue_alloc_element elem 0x5d041099ffd0 size 56 in_num 0 out_num 1
> virtqueue_pop vq 0x5d0410d87168 elem 0x5d041099ffd0 in_num 0 out_num 1
> virtqueue_fill vq 0x5d0410d87168 elem 0x5d041099ffd0 len 0 idx 0
> virtqueue_flush vq 0x5d0410d87168 count 1
> virtio_notify vdev 0x5d0410d79a10 vq 0x5d0410d87168
>
> There's no reception. I used wireshark to inspect the packets that are
> being sent and received through the tap device in L0.
>
> When pinging L0 from L2, I see one of the following two outcomes:
>
> Outcome 1:
> ----------
> L2 broadcasts ARP packets and L0 replies to L2.
>
> Source Destination Protocol Length Info
> 52:54:00:12:34:57 Broadcast ARP 42 Who has
> 111.1.1.1? Tell 111.1.1.2
> d2:6d:b9:61:e1:9a 52:54:00:12:34:57 ARP 42 111.1.1.1 is at
> d2:6d:b9:61:e1:9a
>
> Outcome 2 (less frequent):
> --------------------------
> L2 sends an ICMP echo request packet to L0 and L0 sends a reply,
> but the reply is not received by L2.
>
> Source Destination Protocol Length Info
> 111.1.1.2 111.1.1.1 ICMP 98 Echo (ping)
> request id=0x0006, seq=1/256, ttl=64
> 111.1.1.1 111.1.1.2 ICMP 98 Echo (ping) reply
> id=0x0006, seq=1/256, ttl=64
>
> When pinging L2 from L0 I get the following output in
> wireshark:
>
> Source Destination Protocol Length Info
> 111.1.1.1 111.1.1.2 ICMP 100 Echo (ping)
> request id=0x002c, seq=2/512, ttl=64 (no response found!)
>
> I do see a lot of traced lines being printed (by the QEMU instance that
> was started in L0) with in_num > 1, for example:
>
> virtqueue_alloc_element elem 0x5d040fdbad30 size 56 in_num 1 out_num 0
> virtqueue_pop vq 0x5d04109b0c50 elem 0x5d040fdbad30 in_num 1 out_num 0
> virtqueue_fill vq 0x5d04109b0c50 elem 0x5d040fdbad30 len 76 idx 0
> virtqueue_flush vq 0x5d04109b0c50 count 1
> virtio_notify vdev 0x5d04109a8d50 vq 0x5d04109b0c50
>
So L0 is able to receive data from L2. We're halfway there, Good! :).
> It looks like L1 is receiving data from L0 but this is not related to
> the pings that are sent from L2. I haven't figured out what data is
> actually being transferred in this case. It's not necessary for all of
> the data that L1 receives from L0 to be passed to L2, is it?
>
It should be noise, yes.
> >>>> For svq->vring.num = 256, the following line is
> >>>> printed 20 times,
> >>>>
> >>>> size: 256, len: 0, i: 0
> >>>>
> >>>> followed by:
> >>>>
> >>>> size: 256, len: 0, i: 1
> >>>> size: 256, len: 0, i: 1
> >>>>
> >>>
> >>> This makes sense for the tx queue too. Can you print the VirtQueue index?
> >>
> >> For svq->vring.num = 64, the vq index is 2. So the following line
> >> (svq->vring.num, used_elem.len, used_elem.id, svq->vq->queue_index)
> >> is printed repeatedly:
> >>
> >> size: 64, len: 1, i: 0, vq idx: 2
> >>
> >> For svq->vring.num = 256, the following line is repeated several
> >> times:
> >>
> >> size: 256, len: 0, i: 0, vq idx: 1
> >>
> >> This is followed by:
> >>
> >> size: 256, len: 0, i: 1, vq idx: 1
> >>
> >> In both cases, queue_index is 1.
>
> I also noticed that there are now some lines with svq->vring.num = 256
> where len > 0. These lines were printed by the QEMU instance running
> in L1, so this corresponds to data that was received by L2.
>
> svq->vring.num used_elem.len used_elem.id svq->vq->queue_index
> size: 256 len: 82 i: 0 vq idx: 0
> size: 256 len: 82 i: 1 vq idx: 0
> size: 256 len: 82 i: 2 vq idx: 0
> size: 256 len: 54 i: 3 vq idx: 0
>
> I still haven't figured out what data was received by L2 but I am
> slightly confused as to why this data was received by L2 but not
> the ICMP echo replies sent by L0.
>
We're on a good track, let's trace it deeper. I guess these are
printed from vhost_svq_flush, right? Do virtqueue_fill,
virtqueue_flush, and event_notifier_set(&svq->svq_call) run properly,
or do you see anything strange with gdb / tracing?
