[Bug 1799102] Re: WARNING on boot in Intel GVT-g guest

What causes this WARNING is the host kernel.

Using latest drm-tip (d63c50f2b014037b43c1c0f108c61e0a31ede3c1) in the
host, there is no WARNING in the guest, while the WARNING happens when
the host uses 4.18.0-12 (HWE 18.04 Edge). 4.15.0-42 does not support
iGVT-g with dma-buf, so it's not useful to test.

It seems the results weren't dependent of the Linux kernel version on
the guest: they were the same with 4.18.0-11, 4.18.0-12 and 4.19.5.

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https://bugs.launchpad.net/bugs/1799102

Title:
WARNING on boot in Intel GVT-g guest

Status in linux package in Ubuntu:
Confirmed

Bug description:
When booting Ubuntu Cosmic Cuttlefish 18.10 in an Intel GVT-g Virtual
Machine, a kernel WARNING appears in dmesg, with the following:

[ 3.563734] WARNING: CPU: 3 PID: 346 at
drivers/gpu/drm/i915/i915_irq.c:161 gen3_assert_iir_is_zero+0x38/0xa0
[i915]

I have not noticed negative effects in the VM, but a kernel WARNING
probably has relevance.

While I added a custom EDID to fix resolution, the WARNING happens
without custom EDID set too. I will add information about the host in
the next message.

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: linux-image-4.18.0-10-generic 4.18.0-10.11
ProcVersionSignature: User Name 4.18.0-10.11-generic 4.18.12
Uname: Linux 4.18.0-10-generic x86_64
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC1: ubuntu 1896 F.... pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Sun Oct 21 19:44:44 2018
InstallationDate: Installed on 2018-10-18 (3 days ago)
InstallationMedia: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
IwConfig:
lo no wireless extensions.

ens8 no wireless extensions.
Lsusb:
Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 003: ID 46f4:0002
Bus 002 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.18.0-10-generic root=UUID=6cb7fc66-eb2c-4203-9d7d-2aa2665911ac ro quiet splash drm.edid_firmware=EDID_E1941.bin log_buf_len=16M vt.handoff=1
RelatedPackageVersions:
linux-restricted-modules-4.18.0-10-generic N/A
linux-backports-modules-4.18.0-10-generic N/A
linux-firmware 1.175
RfKill:

SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/06/2015
dmi.bios.vendor: EFI Development Kit II / OVMF
dmi.bios.version: 0.0.0
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-i440fx-3.0
dmi.modalias: dmi:bvnEFIDevelopmentKitII/OVMF:bvr0.0.0:bd02/06/2015:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-3.0:cvnQEMU:ct1:cvrpc-i440fx-3.0:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-3.0
dmi.sys.vendor: QEMU

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