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i915.alpha_support breaks gpu passthrough


WashingtonMatt

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I'm running two VM's with gpu passthrough. In order to enable Plex hardware encoding on the intel IGD,I have to use i915.alpha_support=1 in syslinux.config (works great). Unfortunately, that breaks the gpu passthrough on one of the VMs(Win10). The GPU passthrough that breaks is an old AMD Radeon HD 2400 pro/xt in PCIe 2 or 3(boot hang). I'm not sure if the age is the issue, or something else. The other VM(osx) with Radeon RX 560 in PCIe 1 continues to work fine. I'm not sure where to go from here in troubleshooting. Suspect I'm approaching a unraid reboot record... I'd really like to make use of the IGD.

 

edit: Win10 VM is using seabios. Have not tried OVMF yet

 

M/B: Gigabyte Technology Co., Ltd. - Z370 AORUS Gaming 7
CPU: Intel® Core™ i7-8700 CPU @ 3.20GHz
HVM: Enabled
IOMMU: Enabled
Cache: 384 kB, 1536 kB, 12288 kB
Memory: 32 GB (max. installable capacity 64 GB)
Network: eth0: 1000 Mb/s, full duplex, mtu 1500 
 eth1: not connected
Kernel: Linux 4.14.49-unRAID x86_64

 

syslinux.config - to get on-board intel audio passthrough working

  append pcie_acs_override=downstream vfio-pci.ids=8086:a2f0,8086:a2a3,8086:a2a1 initrd=/bzroot

IOMMU group 0:	[8086:3ec2] 00:00.0 Host bridge: Intel Corporation 8th Gen Core Processor Host Bridge/DRAM Registers (rev 07)
IOMMU group 1:	[8086:1901] 00:01.0 PCI bridge: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor PCIe Controller (x16) (rev 07)
IOMMU group 2:	[8086:3e92] 00:02.0 VGA compatible controller: Intel Corporation Device 3e92
IOMMU group 3:	[8086:1911] 00:08.0 System peripheral: Intel Corporation Xeon E3-1200 v5/v6 / E3-1500 v5 / 6th/7th Gen Core Processor Gaussian Mixture Model
IOMMU group 4:	[8086:a2af] 00:14.0 USB controller: Intel Corporation 200 Series PCH USB 3.0 xHCI Controller
IOMMU group 5:	[8086:a2ba] 00:16.0 Communication controller: Intel Corporation 200 Series PCH CSME HECI #1
IOMMU group 6:	[8086:a282] 00:17.0 SATA controller: Intel Corporation 200 Series PCH SATA controller [AHCI mode]
IOMMU group 7:	[8086:a2e7] 00:1b.0 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #17 (rev f0)
IOMMU group 8:	[8086:a2e9] 00:1b.2 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #19 (rev f0)
IOMMU group 9:	[8086:a2eb] 00:1b.4 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #21 (rev f0)
IOMMU group 10:	[8086:a2ed] 00:1b.6 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #23 (rev f0)
IOMMU group 11:	[8086:a290] 00:1c.0 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #1 (rev f0)
IOMMU group 12:	[8086:a291] 00:1c.1 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #2 (rev f0)
IOMMU group 13:	[8086:a292] 00:1c.2 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #3 (rev f0)
IOMMU group 14:	[8086:a294] 00:1c.4 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #5 (rev f0)
IOMMU group 15:	[8086:a296] 00:1c.6 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #7 (rev f0)
IOMMU group 16:	[8086:a298] 00:1d.0 PCI bridge: Intel Corporation 200 Series PCH PCI Express Root Port #9 (rev f0)
IOMMU group 17:	[8086:a2c9] 00:1f.0 ISA bridge: Intel Corporation Device a2c9
[8086:a2a1] 00:1f.2 Memory controller: Intel Corporation 200 Series PCH PMC
[8086:a2f0] 00:1f.3 Audio device: Intel Corporation 200 Series PCH HD Audio
[8086:a2a3] 00:1f.4 SMBus: Intel Corporation 200 Series PCH SMBus Controller
IOMMU group 18:	[8086:15b8] 00:1f.6 Ethernet controller: Intel Corporation Ethernet Connection (2) I219-V
IOMMU group 19:	[1002:67ff] 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Baffin [Radeon RX 550 640SP / RX 560/560X] (rev cf)
[1002:aae0] 01:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Device aae0
IOMMU group 20:	[144d:a808] 04:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981
IOMMU group 21:	[1002:94c1] 05:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV610 [Radeon HD 2400 PRO/XT]
IOMMU group 22:	[1969:e0b1] 08:00.0 Ethernet controller: Qualcomm Atheros Killer E2500 Gigabit Ethernet Controller (rev 10)
IOMMU group 23:	[1b21:2142] 09:00.0 USB controller: ASMedia Technology Inc. Device 2142
IOMMU group 24:	[1b21:2142] 0a:00.0 USB controller: ASMedia Technology Inc. Device 2142
IOMMU group 25:	[144d:a808] 0b:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller SM981/PM981

 

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And now it's working ?‍♂️. I made a OVMF Win10 vm and it started up fine. So I tried the seabios Win10 VM and it worked too. Started OSX vm and it complained about the mouse no longer being detected. Re-edited that vm real quick and everything is happy including plex hardware transcoding.

 

My best guess at this point is one of the USB devices was interfering with the gpu. I suspect I haven't seen the last of this problem. Advice welcome!

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