10:27 p.m.
Hi,
We are seeing an issue with udambuf, where it says "open /dev/udmabuf: No such file
or directory " even if the device exits. This issue particularly we are seeing with
libvirt. When we run the QEMU args on the command line, everything works as expected.
It seems to be some permission issue when we use the Libvirt, please help us on resolving
this.
[cid:image001.png@01D817A5.0151F260]
Libvirt Version: 6.0.0
Host: Ubuntu 21.04
QEMU commands:
qemu-system-x86_64 \
-enable-kvm \
-smp cores=4,threads=2,sockets=1 \
-m 4096 \
-name win-vm-0 \
-cpu host \
-drive id=windows_drive,if=virtio,file=/win10_enterprise.qcow2,format=qcow2,cache=none \
-device vfio-pci,host=0000:00:02.2 \
-device e1000,netdev=net0,mac=00:a1:00:00:00:10 \
-netdev user,id=net0,ipv6=off,hostfwd=tcp::1111-:22,hostfwd=tcp::3389-:3389 \
-monitor tcp:127.0.0.1:11111,server,nowait \
-rtc base=localtime \
-usb \
-device usb-tablet \
-device usb-kbd \
-device usb-mouse \
-device virtio-vga,blob=true \
-display gtk,gl=on \
-object memory-backend-memfd,id=mem1,hugetlb=off,size=4096M \
-machine memory-backend=mem1
Libvirt XML:
<?xml version="1.0"?>
<domain xmlns:qemu=http://libvirt.org/schemas/domain/qemu/1.0 type="kvm">
<name>win-vm-0</name>
<memory unit="KiB">4194304</memory>
<currentMemory unit="KiB">4194304</currentMemory>
<memoryBacking supported="yes">
<source type="memfd"/>
</memoryBacking>
<vcpu>6</vcpu>
<os>
<type arch="x86_64" machine="pc">hvm</type>
<boot dev="hd"/>
<boot dev="cdrom"/>
</os>
<features>
<acpi/>
<apic/>
<hyperv>
<relaxed state="on"/>
<vapic state="on"/>
<spinlocks state="on" retries="8191"/>
</hyperv>
<vmport state="off"/>
</features>
<cpu mode="host-model">
<model fallback="forbid"/>
</cpu>
<clock offset="utc">
</clock>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>
<devices>
<emulator>/usr/bin/qemu-system-x86_64</emulator>
<disk type="file" device="disk">
<driver name="qemu" type="qcow2"/>
<source file="/win10_enterprise.qcow2" index="1"/>
<backingStore/>
<target dev="sda" bus="sata"/>
<alias name="sata0-0-0"/>
<address type="drive" controller="0" bus="0"
target="0" unit="0"/>
</disk>
<interface type="bridge">
<source bridge="br0"/>
<model type="virtio"/>
</interface>
<serial type="pty">
<target port="0"/>
<target type="serial" port="0">
</target>
<alias name="serial0"/>
</serial>
<console type="pty">
<target type="serial" port="0"/>
<alias name="serial0"/>
</console>
<hostdev mode="subsystem" type="pci"
managed="yes">
<driver name="vfio"/>
<source>
<address domain="0x0000" bus="0x00" slot="0x02"
function="0x02"/>
</source>
</hostdev>
</devices>
<qemu:commandline>
<qemu:arg value="-device"/>
<qemu:arg value="virtio-vga,blob=true"/>
<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on"/>
<qemu:env name="DISPLAY" value=":1.0"/>
</qemu:commandline>
</domain>
Thanks,
Shiv
10:39 p.m.
On Tue, Feb 01, 2022 at 14:27:55 +0000, M, Shivakumar wrote:
Hi,
We are seeing an issue with udambuf, where it says "open /dev/udmabuf: No such file
or directory " even if the device exits. This issue particularly we are seeing with
libvirt. When we run the QEMU args on the command line, everything works as expected.
It seems to be some permission issue when we use the Libvirt, please help us on resolving
this.
libvirt runs qemu in a mount namespace where we propagate only nodes
from /dev/ which are know and used by libvirt so that the qemu proces is
confined to only what it needs.
Ideally you'll impelemt the support for the 'blob' parameter you are
using in a way which allows the use of the appropriate files for qemu:
Libvirt XML:
<?xml version="1.0"?>
<domain xmlns:qemu=http://libvirt.org/schemas/domain/qemu/1.0
type="kvm">
<name>win-vm-0</name>
<memory unit="KiB">4194304</memory>
<currentMemory unit="KiB">4194304</currentMemory>
<memoryBacking supported="yes">
<source type="memfd"/>
</memoryBacking>
<vcpu>6</vcpu>
<os>
<type arch="x86_64" machine="pc">hvm</type>
<boot dev="hd"/>
<boot dev="cdrom"/>
</os>
<features>
<acpi/>
<apic/>
<hyperv>
<relaxed state="on"/>
<vapic state="on"/>
<spinlocks state="on" retries="8191"/>
</hyperv>
<vmport state="off"/>
</features>
<cpu mode="host-model">
<model fallback="forbid"/>
</cpu>
<clock offset="utc">
</clock>
<on_poweroff>destroy</on_poweroff>
<on_reboot>restart</on_reboot>
<on_crash>destroy</on_crash>
<devices>
<emulator>/usr/bin/qemu-system-x86_64</emulator>
<disk type="file" device="disk">
<driver name="qemu" type="qcow2"/>
<source file="/win10_enterprise.qcow2" index="1"/>
<backingStore/>
<target dev="sda" bus="sata"/>
<alias name="sata0-0-0"/>
<address type="drive" controller="0" bus="0"
target="0" unit="0"/>
</disk>
<interface type="bridge">
<source bridge="br0"/>
<model type="virtio"/>
</interface>
<serial type="pty">
<target port="0"/>
<target type="serial" port="0">
</target>
<alias name="serial0"/>
</serial>
<console type="pty">
<target type="serial" port="0"/>
<alias name="serial0"/>
</console>
<hostdev mode="subsystem" type="pci"
managed="yes">
<driver name="vfio"/>
<source>
<address domain="0x0000" bus="0x00" slot="0x02"
function="0x02"/>
</source>
</hostdev>
</devices>
<qemu:commandline>
<qemu:arg value="-device"/>
<qemu:arg value="virtio-vga,blob=true"/>
<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on"/>
<qemu:env name="DISPLAY" value=":1.0"/>
Libvirt doesn't interpret this in any way so you'll need to implement
support for what you want.
Alternatively as a proof-of-concept/workaround you can set the
'cgroup_device_acl' setting in /etc/libvirt/qemu.conf. But as noted that
is not really a supportable solution.
10:41 p.m.
On Tue, Feb 01, 2022 at 02:27:55PM +0000, M, Shivakumar wrote:
Hi,
We are seeing an issue with udambuf, where it says "open /dev/udmabuf: No such file
or directory " even if the device exits. This issue particularly we are seeing with
libvirt. When we run the QEMU args on the command line, everything works as expected.
It seems to be some permission issue when we use the Libvirt, please help us on resolving
this.
When libvirt launches QEMU it puts in place a number of strict
security protections. Libvirt will grant access on a per-file
basis to resources on the host that QEMU should be allowed to
access based on the device configuration in the XML.
In your case though you're using command line passthrough:
<qemu:commandline>
<qemu:arg value="-device"/>
<qemu:arg value="virtio-vga,blob=true"/>
<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on"/>
<qemu:env name="DISPLAY" value=":1.0"/>
</qemu:commandline>
This is totally opaque to libvirt and so libvirt won't be
granting access to any resources needed by these args. I'm
assuming /dev/udmabuf is needed by the GTK display for GL
support, or something along those lines.
For further information about your options please consult this page:
https://libvirt.org/kbase/qemu-passthrough-security.html
Regards,
Daniel
--
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10:53 p.m.
Hi Daniel,
You're right , /dev/udmabuf is required for GTK display for GL support. I agree
passing the device using qemu:arg breaks the security confinement of Libvirt. For our
use-case we need to have the GL support, is there any way to specify the GTK display
option in the Libvirt XML ? or any other alternatives?
Thanks,
Shiv
-----Original Message-----
From: Daniel P. Berrangé <berrange(a)redhat.com>
Sent: Tuesday, February 1, 2022 8:11 PM
To: M, Shivakumar <shivakumar.m(a)intel.com>
Cc: libvirt-users(a)redhat.com
Subject: Re: udmabuf error with libvirt + QEMU
On Tue, Feb 01, 2022 at 02:27:55PM +0000, M, Shivakumar wrote:
Hi,
We are seeing an issue with udambuf, where it says "open /dev/udmabuf: No such file
or directory " even if the device exits. This issue particularly we are seeing with
libvirt. When we run the QEMU args on the command line, everything works as expected.
It seems to be some permission issue when we use the Libvirt, please help us on resolving
this.
When libvirt launches QEMU it puts in place a number of strict security protections.
Libvirt will grant access on a per-file basis to resources on the host that QEMU should be
allowed to access based on the device configuration in the XML.
In your case though you're using command line passthrough:
<qemu:commandline>
<qemu:arg value="-device"/>
<qemu:arg value="virtio-vga,blob=true"/>
<qemu:arg value="-display"/>
<qemu:arg value="gtk,gl=on"/>
<qemu:env name="DISPLAY" value=":1.0"/>
</qemu:commandline>
This is totally opaque to libvirt and so libvirt won't be granting access to any
resources needed by these args. I'm assuming /dev/udmabuf is needed by the GTK display
for GL support, or something along those lines.
For further information about your options please consult this page:
https://libvirt.org/kbase/qemu-passthrough-security.html
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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3 comments
3 participants
participants (3)
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Daniel P. Berrangé -
M, Shivakumar -
Peter Krempa