Re: [RFC v3 3/3] vhost: Allocate memory for packed vring

[Sahil]

Hi,

On Friday, August 30, 2024 4:18:31 PM GMT+5:30 Eugenio Perez Martin wrote:
> On Fri, Aug 30, 2024 at 12:20 PM Sahil <icegambit91@gmail.com> wrote:
> > Hi,
> > 
> > On Tuesday, August 27, 2024 9:00:36 PM GMT+5:30 Eugenio Perez Martin wrote:
> > > On Wed, Aug 21, 2024 at 2:20 PM Sahil <icegambit91@gmail.com> wrote:
> > > > [...]
> > > > I have been trying to test my changes so far as well. I am not very
> > > > clear
> > > > on a few things.
> > > > 
> > > > Q1.
> > > > I built QEMU from source with my changes and followed the vdpa_sim +
> > > > vhost_vdpa tutorial [1]. The VM seems to be running fine. How do I
> > > > check
> > > > if the packed format is being used instead of the split vq format for
> > > > shadow virtqueues? I know the packed format is used when virtio_vdev
> > > > has
> > > > got the VIRTIO_F_RING_PACKED bit enabled. Is there a way of checking
> > > > that
> > > > this is the case?
> > > 
> > > You can see the features that the driver acked from the guest by
> > > checking sysfs. Once you know the PCI BFN from lspci:
> > > # lspci -nn|grep '\[1af4:1041\]'
> > > 01:00.0 Ethernet controller [0200]: Red Hat, Inc. Virtio 1.0 network
> > > device [1af4:1041] (rev 01)
> > > # cut -c 35
> > > /sys/devices/pci0000:00/0000:00:02.0/0000:01:00.0/virtio0/features 0
> > > 
> > > Also, you can check from QEMU by simply tracing if your functions are
> > > being called.
> > > 
> > > > Q2.
> > > > What's the recommended way to see what's going on under the hood? I
> > > > tried
> > > > using the -D option so QEMU's logs are written to a file but the file
> > > > was
> > > > empty. Would using qemu with -monitor stdio or attaching gdb to the
> > > > QEMU
> > > > VM be worthwhile?
> > > 
> > > You need to add --trace options with the regex you want to get to
> > > enable any output. For example, --trace 'vhost_vdpa_*' print all the
> > > trace_vhost_vdpa_* functions.
> > > 
> > > If you want to speed things up, you can just replace the interesting
> > > trace_... functions with fprintf(stderr, ...). We can add the trace
> > > ones afterwards.
> > 
> > Understood. I am able to trace the functions that are being called with
> > fprintf. I'll stick with fprintf for now.
> > 
> > I realized that packed vqs are not being used in the test environment. I
> > see that in "hw/virtio/vhost-shadow-virtqueue.c", svq->is_packed is set
> > to 0 and that calls vhost_svq_add_split(). I am not sure how one enables
> > the packed feature bit. I don't know if this is an environment issue.
> > 
> > I built qemu from the latest source with my changes on top of it. I
> > followed this article [1] to set up the environment.
> > 
> > On the host machine:
> > 
> > $ uname -a
> > Linux fedora 6.10.5-100.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Wed Aug 14
> > 15:49:25 UTC 2024 x86_64 GNU/Linux
> > 
> > $ ./qemu/build/qemu-system-x86_64 --version
> > QEMU emulator version 9.0.91
> > 
> > $ vdpa -V
> > vdpa utility, iproute2-6.4.0
> > 
> > All the relevant vdpa modules have been loaded in accordance with [1].
> > 
> > $ lsmod | grep -iE "(vdpa|virtio)"
> > vdpa_sim_net    12288  0
> > vdpa_sim                24576  1 vdpa_sim_net
> > vringh          32768  2 vdpa_sim,vdpa_sim_net
> > vhost_vdpa              32768  2
> > vhost           65536  1 vhost_vdpa
> > vhost_iotlb             16384  4 vdpa_sim,vringh,vhost_vdpa,vhost
> > vdpa            36864  3 vdpa_sim,vhost_vdpa,vdpa_sim_net
> > 
> > $ ls -l /sys/bus/vdpa/devices/vdpa0/driver
> > lrwxrwxrwx. 1 root root 0 Aug 30 11:25 /sys/bus/vdpa/devices/vdpa0/driver
> > -> ../../bus/vdpa/drivers/vhost_vdpa
> > 
> > In the output of the following command, I see ANY_LAYOUT is supported.
> > According to virtio_config.h [2] in the linux kernel, this represents the
> > layout of descriptors. This refers to split and packed vqs, right?
> > 
> > $ vdpa mgmtdev show
> > 
> > vdpasim_net:
> >   supported_classes net
> >   max_supported_vqs 3
> >   dev_features MTU MAC STATUS CTRL_VQ CTRL_MAC_ADDR ANY_LAYOUT VERSION_1
> >   ACCESS_PLATFORM> 
> > $ vdpa dev show -jp
> > {
> > 
> >     "dev": {
> >     
> >         "vdpa0": {
> >         
> >             "type": "network",
> >             "mgmtdev": "vdpasim_net",
> >             "vendor_id": 0,
> >             "max_vqs": 3,
> >             "max_vq_size": 256
> >         
> >         }
> >     
> >     }
> > 
> > }
> > 
> > I started the VM by running:
> > 
> > $ sudo ./qemu/build/qemu-system-x86_64 \
> > -enable-kvm \
> > -drive file=//home/ig91/fedora_qemu_test_vm/L1.qcow2,media=disk,if=virtio
> > \
> > -net nic,model=virtio \
> > -net user,hostfwd=tcp::2226-:22 \
> > -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0 \
> > -device
> > virtio-net-pci,netdev=vhost-vdpa0,bus=pci.0,addr=0x7,disable-legacy=on,di
> > sable-modern=off,page-per-vq=on,event_idx=off,packed=on \ -nographic \
> > -m 2G \
> > -smp 2 \
> > -cpu host \
> > 2>&1 | tee vm.log
> > 
> > I added the packed=on option to -device virtio-net-pci.
> > 
> > In the VM:
> > 
> > # uname -a
> > Linux fedora 6.8.5-201.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Apr 11
> > 18:25:26 UTC 2024 x86_64 GNU/Linux
> > 
> > # lspci -nn | grep -i -A15 "\[1af4:1041\]"
> > 00:07.0 Ethernet controller [0200]: Red Hat, Inc. Virtio 1.0 network
> > device [1af4:1041] (rev 01)
> > 
> > # cut -c 35 /sys/devices/pci0000:00/0000:00:07.0/virtio1/features
> > 0
> > 
> > The packed vq feature bit hasn't been set. Am I missing something here?
> 
> vdpa_sim does not support packed vq at the moment. You need to build
> the use case #3 of the second part of that blog [1]. It's good that
> you build the vdpa_sim earlier as it is a simpler setup.
> 
> If you have problems with the vp_vdpa environment please let me know
> so we can find alternative setups.

Thank you for the clarification. I tried setting up the vp_vdpa
environment (scenario 3) but I ended up running into a problem
in the L1 VM.

I verified that nesting is enabled in KVM (L0):

$ grep -oE "(vmx|svm)" /proc/cpuinfo | sort | uniq
vmx

$ cat /sys/module/kvm_intel/parameters/nested
Y

There are no issues when booting L1. I start the VM by running:

$ sudo ./qemu/build/qemu-system-x86_64 \
-enable-kvm \
-drive file=//home/ig91/fedora_qemu_test_vm/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,event_idx=off,packed=on,bus=pcie.0,addr=0x4
 \
-netdev tap,id=net0,script=no,downscript=no \
-nographic \
-m 2G \
-smp 2 \
-M q35 \
-cpu host \
2>&1 | tee vm.log

Kernel version in L1:

# uname -a
Linux fedora 6.8.5-201.fc39.x86_64 #1 SMP PREEMPT_DYNAMIC Thu Apr 11 18:25:26 
UTC 2024 x86_64 GNU/Linux

The following variables are set in the kernel's config as
described in the blog [1]:

CONFIG_VIRTIO_VDPA=m
CONFIG_VDPA=m
CONFIG_VP_VDPA=m
CONFIG_VHOST_VDPA=m

The vDPA tool also satisfies the version criterion.

# vdpa -V
vdpa utility, iproute2-6.10.0

I built QEMU from source with my changes on top of it.

# ./qemu/build/qemu-system-x86_64 --version
QEMU emulator version 9.0.91

The relevant vdpa modules are loaded successfully as
explained in the blog.

# lsmod | grep -i vdpa
vp_vdpa         20480  0
vhost_vdpa      32768  0
vhost                   65536  1 vhost_vdpa
vhost_iotlb    16384  2 vhost_vdpa,vhost
vdpa               36864  2 vp_vdpa,vhost_vdpa
irqbypass       12288  2 vhost_vdpa,kvm

# lspci | grep -i virtio
00:03.0 SCSI storage controller: Red Hat, Inc. Virtio block device
00:04.0 Ethernet controller: Red Hat, Inc. Virtio 1.0 network device (rev 01)

# lspci -n |grep 00:04.0
00:04.0 0200: 1af4:1041 (rev 01)

I then unbind the virtio-pci device from the virtio-pci
driver and bind it to the vp_vdpa driver.

# echo 0000:00:04.0 > /sys/bus/pci/drivers/virtio-pci/unbind
# echo 1af4 1041 > /sys/bus/pci/drivers/vp-vdpa/new_id

I then create the vDPA device without any issues.

# vdpa mgmtdev show
pci/0000:00:04.0: 
  supported_classes net
  max_supported_vqs 3
  dev_features CSUM GUEST_CSUM CTRL_GUEST_OFFLOADS MAC GUEST_TSO4 GUEST_TSO6 
GUEST_ECN GUEST_UFO HOST_TSO4 HOST_TSO6 HOST_ECN HOST_UFO MRG_RXBUF STATUS 
CTRL_VQ CTRL_RX CTRL_VLAN CTRL_RX_EXTRA GUEST_ANNOUNCE CTRL_MAC_ADDR 
RING_INDIRECT_DE6

# vdpa dev add name vdpa0 mgmtdev pci/0000:00:04.0
# vdpa dev show -jp
{
    "dev": {
        "vdpa0": {
            "type": "network",
            "mgmtdev": "pci/0000:00:04.0",
            "vendor_id": 6900,
            "max_vqs": 3,
            "max_vq_size": 256
        }
    }
}

# ls -l /sys/bus/vdpa/devices/vdpa0/driver
lrwxrwxrwx. 1 root root 0 Sep  8 18:58 /sys/bus/vdpa/devices/vdpa0/driver -> 
../../../../bus/vdpa/drivers/vhost_vdpa

# ls -l /dev/ |grep vdpa
crw-------. 1 root root    239,   0 Sep  8 18:58 vhost-vdpa-0

# driverctl -b vdpa list-devices
vdpa0 vhost_vdpa

I have a qcow2 image L2.qcow in L1. QEMU throws an error
when trying to launch L2.

# sudo ./qemu/build/qemu-system-x86_64 \
-enable-kvm \
-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,bus=pcie.0,addr=0x7,disable-legacy=on,disable-modern=off,event_idx=off,packed=on
 \
-nographic \
-m 2G \
-smp 2 \
-M q35 \
-cpu host \
2>&1 | tee vm.log

qemu-system-x86_64: -netdev 
type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0: Could not open 
'/dev/vhost-vdpa-0': Unknown error 524

I get the same error when trying to launch L2 with qemu-kvm
which I installed using "dnf install".

# qemu-kvm --version
QEMU emulator version 8.1.3 (qemu-8.1.3-5.fc39)

The minimum version of QEMU required is v7.0.0-rc4.

According to "include/linux/errno.h" [2], errno 524 is
ENOTSUPP (operation is not supported). I am not sure
where I am going wrong.

However, I managed to set up scenario 4 successfully
and I see that packed vq is enabled in this case.

# cut -c 35 /sys/devices/pci0000:00/0000:00:04.0/virtio1/features
1

For the time being, shall I simply continue testing with
scenario 4?

> Thanks!
> 
> [1]
> https://www.redhat.com/en/blog/hands-vdpa-what-do-you-do-when-you-aint-got-
> hardware-part-2
> > Thanks,
> > Sahil
> > 
> > [1]
> > https://www.redhat.com/en/blog/hands-vdpa-what-do-you-do-when-you-aint-go
> > t-hardware-part-1 [2]
> > https://github.com/torvalds/linux/blob/master/include/uapi/linux/virtio_c
> > onfig.h#L63

Thanks,
Sahil

[1] 
https://www.redhat.com/en/blog/hands-vdpa-what-do-you-do-when-you-aint-got-hardware-part-2
[2] https://github.com/torvalds/linux/blob/master/include/linux/errno.h#L27