QEMU/KVM and GPU Passthrough Troubleshooting

Guest GPU Au­dio Crack­ling and IRQ xx: No­body Cared Fix

Win­dows

The so­lu­tion of the is­sue Guest GPU HD­MI Au­dio Crack­ling, Bro­ken or Los­ing is well ex­plained by Jonp at UN­RAID Fo­rums. In short we must try to en­able the MSI – Mes­sage Sig­naled In­ter­rupts op­tion if the de­vice sup­port it. Here is a de­tailed step-by-step in­struc­tion how to do that.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 1: Open De­vice Man­ag­er and from the View menu switch to Re­sources by type.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 2: Ex­pand the sec­tion In­ter­rupt re­quest (IRQ).

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 3: Find the prob­lem­at­ic au­dio de­vice and by the con­text menu choice Prop­er­ties.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 4: With­in the De­tails tab witch to Prop­er­ty De­vice in­stance path.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 5: In this par­tic­u­lar case the Val­ue is PCI­\­VEN­_­10­DE­&­DEV­_­0E­08­&­SUB­SYS­_­102­F10­DE­&­REV­_­A1­\­4&­29­fcb­422­&0­&00­16. This is a re­la­ti­ve path to Com­pu­ter­\­HKEY­_­LO­CAL­_­MA­CHI­NE­\­SYS­TEM­\­Cur­rent­Con­trol­Set­\­Enum in the Win­dows 10's regis­try.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 6: Run Reg­istry Ed­i­tor as Ad­min­is­tra­tor.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 7: In the Reg­istry Ed­i­tor tool, paste Com­pu­ter­\­HKEY­_­LO­CAL­_­MA­CHI­NE­\­SYS­TEM­\­Cur­rent­Con­trol­Set­\­Enum in the path line and hit En­ter.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 8: In De­vice Man­ag­er, use the con­text menu and Copy the Val­ue of the tar­get De­vice in­stance path.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 9: In Reg­istry Ed­i­tor ap­pend one back­slash to the path and Paste the Val­ue.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 10: In Reg­istry Ed­i­tor, nav­i­gate to \De­vice Parameters\Interrupt Ma­na­ge­ment\Me­ssa­ge­Sig­na­led­In­ter­rupt­Pro­per­ties.

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 11: Then choose Mod­i­fy from the con­text menu the Val­ue of the DWORD Key MSISup­port­ed (MSI – Mes­sage Sig­naled In­ter­rupts).

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 12: Change the Val­ue of the DWORD Key MSISup­port­ed to 1 [0x0..01].

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 13: Con­firm the change of the DWORD Key MSISup­port­ed (MSI – Mes­sage Sig­naled In­ter­rupts).

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  QE­MU KVM Win­dows Guest Fix NVIDIA NVS 315 HD­MI Au­dio Step 14: Re­boot the guest Op­er­at­ing sys­tem.

I was men­tioned the ker­nel com­mand irqpool as so­lu­tion for this is­sue, but in my opin­ion and ac­cord­ing to some oth­er posts, pro­vid­ed in the ref­er­ences sec­tion, this set­ting is an ac­tu­al so­lu­tion for the prob­lem irq 44: no­body cared (try boot­ing with the "irqpool" op­tion); han­dlers: vfio_​​​intx_​​​handler; Dis­abling IRQ #44, that ap­pears at my sys­tem when boot­ing a VM with GPU passthrough with a dis­play at­tached to it, which was caus­ing host sys­tem re­boot.

Lin­ux

Lin­ux guests usu­al­ly en­able MSI by them­selves. To force use of MSI for GPU au­dio de­vices, use the fol­low­ing com­mand and re­boot.

echo "options snd-hda-intel enable_msi=1" | sudo tee /etc/modprobe.d/snd-hda-intel.conf

sudo update-initramfs -u -k all

Use lsp­ci ‑vv and check for the fol­low­ing line on your de­vice to see if MSI is en­abled.

sudo lspci -nnv -s 09:00

#Out­put

09:00.0 VGA compatible controller [0300]: NVIDIA Corporation TU117GL [T600] [10de:1fb1] (rev a1) (prog-if 00 [VGA controller])
	Subsystem: NVIDIA Corporation TU117GL [T600] [10de:1488]
	Flags: bus master, fast devsel, latency 0, IRQ 103, IOMMU group 23
	Memory at fb000000 (32-bit, non-prefetchable) [size=16M]
	Memory at 7fd0000000 (64-bit, prefetchable) [size=256M]
	Memory at 7fe0000000 (64-bit, prefetchable) [size=32M]
	I/O ports at f000 [size=128]
	Expansion ROM at fc000000 [virtual] [disabled] [size=512K]
	Capabilities: [60] Power Management version 3
	Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [78] Express Legacy Endpoint, MSI 00
	Capabilities: [100] Virtual Channel
	Capabilities: [250] Latency Tolerance Reporting
	Capabilities: [258] L1 PM Substates
	Capabilities: [128] Power Budgeting <?>
	Capabilities: [420] Advanced Error Reporting
	Capabilities: [600] Vendor Specific Information: ID=0001 Rev=1 Len=024 <?>
	Capabilities: [900] Secondary PCI Express
	Capabilities: [bb0] Physical Resizable BAR
	Kernel driver in use: nvidia
	Kernel modules: nouveau, nvidia_drm, nvidia

09:00.1 Audio device [0403]: NVIDIA Corporation Device [10de:10fa] (rev a1)
	Subsystem: NVIDIA Corporation Device [10de:1488]
	Flags: bus master, fast devsel, latency 0, IRQ 99, IOMMU group 23
	Memory at fc080000 (32-bit, non-prefetchable) [size=16K]
	Capabilities: [60] Power Management version 3
	Capabilities: [68] MSI: Enable+ Count=1/1 Maskable- 64bit+
	Capabilities: [78] Express Endpoint, MSI 00
	Capabilities: [100] Advanced Error Reporting
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd_hda_intel

If it says En­able+, MSI is work­ing, En­able- means it is sup­port­ed but dis­abled, and if the line is miss­ing, MSI is not sup­port­ed by the PCIe hard­ware.

This can po­ten­tial­ly al­so im­prove per­for­mance for oth­er passthrough de­vices, in­clud­ing GPUs, but that de­pends on the hard­ware be­ing used.

Ref­er­ences

• UN­RAID Fo­rums: Win­dows 10 VM Los­ing Au­dio
• UN­RAID Fo­rums: Ker­nel Dis­abling IRQ #16
• Red­Hat List­MAN: Ker­nel pan­ic at vfio_​​​intx_​​​handler leads to low per­for­mance in guest VM
• Alex Williamson: VFIO tips and tricks (at vifo​.blogspot​.com): Use­ful­ly Q&A
• Prox­mox Wi­ki: Pci passthrough » HD­MI Au­dio crackling/​​​broken

Hide the Warn­ings KVM: vcpu0 ig­nored rdm­sr

sudo nano /etc/modprobe.d/kvm.conf

options kvm report_ignored_msrs=0 # Or: GRUB_CMDLINE_LINUX_DEFAULT="... kvm.report_ignored_msrs=0 ..."

sudo update-initramfs -u -k all

• Note, ac­cord­ing to my ex­pe­ri­ence, this op­tion may cause crash­es of the host sys­tem!?

Ref­er­ences

• Prox­mox: How to stop warn­ings "kvm: vcpu0 ig­nored rdm­sr"
• ignore_​​​msrs for host CPU be­ing ig­nored

KVM Mod­e­in­fo

modinfo kvm

filename:       /lib/modules/5.4.0-77-generic/kernel/arch/x86/kvm/kvm.ko
license:        GPL
author:         Qumranet
srcversion:     20C68083F39E14AB616D0B8
depends:
retpoline:      Y
intree:         Y
name:           kvm
vermagic:       5.4.0-77-generic SMP mod_unload modversions
sig_id:         PKCS#7
signer:         Build time autogenerated kernel key
sig_key:        67:66:2F:F8:26:8F:56:E9:37:7F:B7:AD:33:FA:97:31:CA:7F:FF:50
sig_hashalgo:   sha512
signature:      6C:0B:65:F9:46:AC:D8:B7:94:E8:B9:9D:A0:4B:97:E6:63:52:5A:FF:
                ...
parm:           nx_huge_pages:bool
parm:           nx_huge_pages_recovery_ratio:uint
parm:           ignore_msrs:bool
parm:           report_ignored_msrs:bool
parm:           min_timer_period_us:uint
parm:           kvmclock_periodic_sync:bool
parm:           tsc_tolerance_ppm:uint
parm:           lapic_timer_advance_ns:int
parm:           vector_hashing:bool
parm:           enable_vmware_backdoor:bool
parm:           force_emulation_prefix:bool
parm:           pi_inject_timer:bint
parm:           halt_poll_ns:uint
parm:           halt_poll_ns_grow:uint
parm:           halt_poll_ns_grow_start:uint
parm:           halt_poll_ns_shrink:uint