RE: udmabuf error with libvirt + QEMU
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
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