Bug 1648236

Support was added upstream by commit:
commit 91e61947eb2be21b00091d34f5692f89cef41376
Author:     Erik Skultety <eskultet>
AuthorDate: Fri Nov 16 11:14:43 2018 +0100
Commit:     Gerd Hoffmann <kraxel>
CommitDate: Fri Nov 16 11:44:22 2018 +0100

    ui: Allow specifying 'rendernode' display option for egl-headless
    
    As libvirt can't predict which rendernode QEMU would pick, it
    won't adjust the permissions on the device, hence QEMU getting
    "Permission denied" when opening the DRI device. Therefore, enable
    'rendernode' option for egl-headless display type.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1648236
    
    Signed-off-by: Erik Skultety <eskultet>
    Message-id: 27f4617f19aa1072114f10f1aa9dd199735ef982.1542362949.git.eskultet
    Signed-off-by: Gerd Hoffmann <kraxel>

Also needed: https://patchwork.ozlabs.org/patch/1001567/

(In reply to Gerd Hoffmann from comment #2)
> Also needed: https://patchwork.ozlabs.org/patch/1001567/

Merged upstream in 3.1, pending backport:

commit e1ca8f7e1915496148f6e0ce1f7c2309af013312
Author: Gerd Hoffmann <kraxel>
Date:   Thu Nov 22 08:16:13 2018 +0100

    qapi: add query-display-options command
    
    Add query-display-options command, which allows querying the qemu
    display configuration.  This isn't particularly useful, except it
    exposes QAPI type DisplayOptions in query-qmp-schema, so that libvirt
    can discover recently added -display parameter rendernode (commit
    d4dc4ab133b).  Works around lack of sufficiently powerful command line
    introspection.
    
    Signed-off-by: Gerd Hoffmann <kraxel>
    Reviewed-by: Eric Blake <eblake>
    Tested-by: Eric Blake <eblake>
    Tested-by: Erik Skultety <eskultet>
    Message-id: 20181122071613.2889-1-kraxel

Fix included in qemu-kvm-rhev-2.12.0-25.el7

Test against qemu-kvm-rhev-2.12.0-24.el7.x86_64 that without rendernode

Scenarios performed:

1) start qemu with /usr/libexec/qemu-kvm -display egl-headless
qemu can start

2) start qemu with /usr/libexec/qemu-kvm -display egl-headless,rendernode=/dev/dri/foo -qmp unix:/tmp/qmp,server,nowait -monitor stdio
qemu can start

3) check qmp commands supported from qemu, there is no command called query-display-options

Test against qemu-kvm-rhev-2.12.0-25.el7.x86_64 that has rendernode

1) can still pass

2) will report error as expected:
(qemu) qemu-kvm: egl: no drm render node available
qemu-kvm: egl: render node init failed

Switch to an existed render provider, qemu can start without error:
# /usr/libexec/qemu-kvm -display egl-headless,rendernode=/dev/dri/renderD128 -qmp unix:/tmp/qmp,server,nowait -monitor stdio
QEMU 2.12.0 monitor - type 'help' for more information
(qemu)

3)check qmp commands supported from qemu, command query-display-options prompt been supported:
{ "execute": "qmp_capabilities" }
{"return": {}}
{ "execute": "query-commands" }
...
{"name": "query-display-options"}
...

4) Execute this qmp command:
{ "execute": "query-display-options"}
{"return": {"type": "egl-headless"}}

5) Execute query-display-options when -display none:
{ "execute": "qmp_capabilities" }
{"return": {}}
{ "execute": "query-display-options"}
{"return": {"type": "none"}}

6) Execute query-display-options when -display option is not specified, vnc and spice has been tried:
{ "execute": "qmp_capabilities" }
{"return": {}}
{ "execute": "query-display-options"}
{"return": {"type": "none"}}

7) boot rhel 7.7 guest with qemu cli
# /usr/libexec/qemu-kvm -display egl-headless -device vfio-pci,sysfsdev=/sys/bus/mdev/devices/89d223b5-8e86-4682-b703-acf28f1fece8,display=on -monitor stdio -cpu Skylake-Client,enforce -m 8G -hda /home/rhel7.qcow2 -vnc :0 -serial unix:/tmp/console,server,nowait guest can boot to desktop and use gvt as desktop provider without problem

Verified per comment 12

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2019:2553