AMD 'Barcelo' passthrough issues - any success stories?

TeddyAstie

EDIT: It looks like I may just have a fake BIOS? The settings to enable all the relevant components (IOMMU, DMAr support etc) don't actually seem to do anything, they might just be for show - dmesg | grep -i iommu returns nothing, dmesg | grep -i -e dmar -e vfio -e pciback only shows pciback info, and cat /proc/cmdline contains nothing about IOMMU. Oddly, XO is still reporting that IOMMU is enabled:

dmesg in the Dom0 will not report the information you're looking for.
To know if PCI Passthrough is supported (e.g IOMMU enabled), you should check xl info | grep virt_caps and look for hvm_directio. You can also look for IOMMU-related stuff in xl dmesg.
As you managed to passthrough the device (even if not working in the guest), I don't see a issue there.

[ 4.655776] amdgpu 0000:00:08.0: amdgpu: Unable to locate a BIOS ROM
[ 4.655797] amdgpu 0000:00:08.0: amdgpu: Fatal error during GPU init
[ 4.655812] amdgpu 0000:00:08.0: amdgpu: amdgpu: finishing device.
[ 4.656681] amdgpu 0000:00:08.0: probe with driver amdgpu failed with error -22

Is there a trick to this, has anyone had success with this kind of AMD GPU? On my old hosts, enabling pass through was enough for it to just kind of work (Intel HD 530). The host machine outputs to a display normally when the card is in-use by the host. I am of the understanding the ROM is just part of the motherboard/GPU, there is some suggestion it can be dumped from the host-side, but I'm unsure on this.

Looks like the GPU ROMBAR is missing in the guest, while it's ok for many devices, many others will fail to work without it (like this GPU).
To me, there's something missing on the PCI Passthrough logic, I just brought the topic internally to see what we can do.

DustyArmstrong

@TeddyAstie Thanks for that - I was going off of other old XCP hosts I have had running that did show IOMMU info there, so I figured it wasn't working on these particular machines. I also had the the Intel GPU working on those hosts, which further supported my theory. I do have a USB controller passed through to the same VM and that works perfectly, basically native functionality, but from the research I was doing it was suggested USB controllers are way less bothered about imperfect passthrough.

I was able to find a ROM for my particular GPU, but I don't know what - if anything - I can do with it in XCP. I've found lots of info for QEMU and Proxmox, but I'm not sure they directly translate.

If there's nothing I can do for the moment then I can live without the GPU, running decode on the CPU isn't really taxing it that much. Appreciate you looking into it.

TeddyAstie

@DustyArmstrong
Can you give the result of :

lspci -vvv -s 00:08.0

(inside Dom0)

Another question, what guest were you trying ?
Can you try with a recent Linux kernel (some changes were made recently regarding video bios requirement) ? Latest Fedora should have a recent enough kernel for testing, that could maybe help workaround the issue in the meantime (and knowing if there are more issues), with no guarantee.

DustyArmstrong

@TeddyAstie Sure no problem.

lspci -vvv -s 00:08.0

00:08.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir PCIe Dummy Host Bridge
	Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-

Host is Debian, slightly older kernel so that may be why? Happy to try a different VM distro if you think it might help.

Linux cctv 6.12.69+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.12.69-1 (2026-02-08) x86_64 GNU/Linux

TeddyAstie

@DustyArmstrong said:

lspci -vvv -s 00:08.0

00:08.0 Host bridge: Advanced Micro Devices, Inc. [AMD] Renoir PCIe Dummy Host Bridge
Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
Status: Cap- 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-

Ah that's not the one I'm looking for.

Can you do lspci -vvv (without the -s ...) and take the part related to the GPU ?

DustyArmstrong

@TeddyAstie yarp.

My bad, the VM has it as 00:08.0 but on the host it's actually 00:06.0, I just didn't think about the specifics of your request!

06:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Barcelo (rev c1) (prog-if 00 [VGA controller])
	Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Device 1636
	Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Interrupt: pin A routed to IRQ 38
	Region 0: Memory at d0000000 (64-bit, prefetchable) [size=256M]
	Region 2: Memory at e0000000 (64-bit, prefetchable) [size=2M]
	Region 4: I/O ports at d000 [size=256]
	Region 5: Memory at fca00000 (32-bit, non-prefetchable) [size=512K]
	Capabilities: [48] Vendor Specific Information: Len=08 <?>
	Capabilities: [50] Power Management version 3
		Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1+,D2+,D3hot+,D3cold+)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [64] Express (v2) Legacy Endpoint, MSI 00
		DevCap:	MaxPayload 256 bytes, PhantFunc 0, Latency L0s <4us, L1 unlimited
			ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset-
		DevCtl:	Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
			RlxdOrd+ ExtTag+ PhantFunc- AuxPwr- NoSnoop+
			MaxPayload 256 bytes, MaxReadReq 512 bytes
		DevSta:	CorrErr- UncorrErr+ FatalErr- UnsuppReq+ AuxPwr- TransPend-
		LnkCap:	Port #0, Speed 8GT/s, Width x16, ASPM L0s L1, Exit Latency L0s <64ns, L1 <1us
			ClockPM- Surprise- LLActRep- BwNot- ASPMOptComp+
		LnkCtl:	ASPM Disabled; RCB 64 bytes Disabled- CommClk+
			ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
		LnkSta:	Speed 8GT/s, Width x16, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
		DevCap2: Completion Timeout: Range ABCD, TimeoutDis+, LTR-, OBFF Not Supported
		DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled
		LnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-
			 Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
			 Compliance De-emphasis: -6dB
		LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete+, EqualizationPhase1+
			 EqualizationPhase2+, EqualizationPhase3+, LinkEqualizationRequest-
	Capabilities: [a0] MSI: Enable- Count=1/4 Maskable- 64bit+
		Address: 0000000000000000  Data: 0000
	Capabilities: [c0] MSI-X: Enable- Count=4 Masked-
		Vector table: BAR=5 offset=00042000
		PBA: BAR=5 offset=00043000
	Capabilities: [100 v1] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
	Capabilities: [270 v1] #19
	Capabilities: [2a0 v1] Access Control Services
		ACSCap:	SrcValid- TransBlk- ReqRedir- CmpltRedir- UpstreamFwd- EgressCtrl- DirectTrans-
		ACSCtl:	SrcValid- TransBlk- ReqRedir- CmpltRedir- UpstreamFwd- EgressCtrl- DirectTrans-
	Capabilities: [2b0 v1] Address Translation Service (ATS)
		ATSCap:	Invalidate Queue Depth: 00
		ATSCtl:	Enable-, Smallest Translation Unit: 00
	Capabilities: [2c0 v1] Page Request Interface (PRI)
		PRICtl: Enable- Reset-
		PRISta: RF- UPRGI- Stopped+
		Page Request Capacity: 00000100, Page Request Allocation: 00000000
	Capabilities: [2d0 v1] Process Address Space ID (PASID)
		PASIDCap: Exec+ Priv+, Max PASID Width: 10
		PASIDCtl: Enable- Exec- Priv-
	Capabilities: [400 v1] #25
	Capabilities: [410 v1] #26
	Capabilities: [440 v1] #27
	Kernel driver in use: pciback

TeddyAstie

@DustyArmstrong said:

@TeddyAstie yarp.

My bad, the VM has it as 00:08.0 but on the host it's actually 00:06.0, I just didn't think about the specifics of your request!

06:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Barcelo (rev c1) (prog-if 00 [VGA controller])
	Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Device 1636
	Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Interrupt: pin A routed to IRQ 38
	Region 0: Memory at d0000000 (64-bit, prefetchable) [size=256M]
	Region 2: Memory at e0000000 (64-bit, prefetchable) [size=2M]
	Region 4: I/O ports at d000 [size=256]
	Region 5: Memory at fca00000 (32-bit, non-prefetchable) [size=512K]
	Capabilities: [48] Vendor Specific Information: Len=08 <?>
	Capabilities: [50] Power Management version 3
		Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA PME(D0-,D1+,D2+,D3hot+,D3cold+)
		Status: D0 NoSoftRst- PME-Enable- DSel=0 DScale=0 PME-
	Capabilities: [64] Express (v2) Legacy Endpoint, MSI 00
		DevCap:	MaxPayload 256 bytes, PhantFunc 0, Latency L0s <4us, L1 unlimited
			ExtTag+ AttnBtn- AttnInd- PwrInd- RBE+ FLReset-
		DevCtl:	Report errors: Correctable- Non-Fatal- Fatal- Unsupported-
			RlxdOrd+ ExtTag+ PhantFunc- AuxPwr- NoSnoop+
			MaxPayload 256 bytes, MaxReadReq 512 bytes
		DevSta:	CorrErr- UncorrErr+ FatalErr- UnsuppReq+ AuxPwr- TransPend-
		LnkCap:	Port #0, Speed 8GT/s, Width x16, ASPM L0s L1, Exit Latency L0s <64ns, L1 <1us
			ClockPM- Surprise- LLActRep- BwNot- ASPMOptComp+
		LnkCtl:	ASPM Disabled; RCB 64 bytes Disabled- CommClk+
			ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
		LnkSta:	Speed 8GT/s, Width x16, TrErr- Train- SlotClk+ DLActive- BWMgmt- ABWMgmt-
		DevCap2: Completion Timeout: Range ABCD, TimeoutDis+, LTR-, OBFF Not Supported
		DevCtl2: Completion Timeout: 50us to 50ms, TimeoutDis-, LTR-, OBFF Disabled
		LnkCtl2: Target Link Speed: 8GT/s, EnterCompliance- SpeedDis-
			 Transmit Margin: Normal Operating Range, EnterModifiedCompliance- ComplianceSOS-
			 Compliance De-emphasis: -6dB
		LnkSta2: Current De-emphasis Level: -3.5dB, EqualizationComplete+, EqualizationPhase1+
			 EqualizationPhase2+, EqualizationPhase3+, LinkEqualizationRequest-
	Capabilities: [a0] MSI: Enable- Count=1/4 Maskable- 64bit+
		Address: 0000000000000000  Data: 0000
	Capabilities: [c0] MSI-X: Enable- Count=4 Masked-
		Vector table: BAR=5 offset=00042000
		PBA: BAR=5 offset=00043000
	Capabilities: [100 v1] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
	Capabilities: [270 v1] #19
	Capabilities: [2a0 v1] Access Control Services
		ACSCap:	SrcValid- TransBlk- ReqRedir- CmpltRedir- UpstreamFwd- EgressCtrl- DirectTrans-
		ACSCtl:	SrcValid- TransBlk- ReqRedir- CmpltRedir- UpstreamFwd- EgressCtrl- DirectTrans-
	Capabilities: [2b0 v1] Address Translation Service (ATS)
		ATSCap:	Invalidate Queue Depth: 00
		ATSCtl:	Enable-, Smallest Translation Unit: 00
	Capabilities: [2c0 v1] Page Request Interface (PRI)
		PRICtl: Enable- Reset-
		PRISta: RF- UPRGI- Stopped+
		Page Request Capacity: 00000100, Page Request Allocation: 00000000
	Capabilities: [2d0 v1] Process Address Space ID (PASID)
		PASIDCap: Exec+ Priv+, Max PASID Width: 10
		PASIDCtl: Enable- Exec- Priv-
	Capabilities: [400 v1] #25
	Capabilities: [410 v1] #26
	Capabilities: [440 v1] #27
	Kernel driver in use: pciback

thanks.

So basically, there is a more annoying issue, as the device doesn't even have a ROMBAR, in this case, the VBIOS is likely in the VFCT ACPI table of host (which the guest can't see); which needs to be injected as a "fake" rombar for the guest to behave properly.

That doable on its own, but it's quite tricky to integrate (and you would e.g need to extract VBIOS from VFCT using external tools).

I just discussed with Xen/AMD people, and there are known issues regarding PCI Passthrough of integrated AMD GPUs (not specific to Xen AFAIU). There are some projects regarding alternative approaches to bring AMD GPUs to VMs (virtio-gpu native context) which is the current focus.

DustyArmstrong

@TeddyAstie Thanks for the update.

I do actually have a VBIOS for that GPU, but I wasn't entirely sure what to do with it - is there a process to inject it? I've found resources for Proxmox and others, but I really like XCP and equally I don't want to migrate my entire setup just for that.

If it's really tricky then I'm not too worried about it, as I say the VM actually runs the cameras perfectly fine on CPU alone, it's negligible.

Edit: Looks like this post might answer my question: https://github.com/xcp-ng/xcp/issues/786

"Even when specifying romfile and rombar properties on the xen-pci-passthrough device in QEMU, the ROM region is not mapped into guest memory."

timemaster5 created this issue in xcp-ng/xcp

open PCI ROM BAR not exposed to guest when using xen-pci-passthrough #786

timemaster5

@DustyArmstrong @teddyastie

Guys, try this https://xcp-ng.org/forum/post/103216

A deep dive is on the linked medium article in that post.

You're right in your findings about the ROMBAR.

It is not a huge problem that is not passed through. What annoys me is that the support for "fake" ROMBAR (config options rombar and romfile) is present in the xen_pci_passthrough QEMU device, but it doesn't work

I found a workaround by using the “loader” QEMU device. This device simply places your vBIOS in the right memory region where the amdgpu driver can find it. It is a quite nice, clean solution, and I hope my pull request for required changes in qemu-wrapper will be integrated soon. In my opinion, it doesn't hurt anything, but I am still waiting.

DustyArmstrong

@timemaster5 Ah very cool, thank you for looking into this and the comprehensive write up, great work. I went on a small journey to try various workarounds but didn't get as far as yourself and others, particularly as my use-case is only a "nice-to-have". Most everything I found was in relation to Proxmox and others. Little did I know when I thought I was helping you over on Github, you would actually end up helping me!

As I understand from your notes, the full procedure would be:

Enable passthrough for the GPU on the host
Apply the patched wrapper to enable custom model args and respect platform vga
Disable emulated VGA via platform:vga=none
Apply the config to the VM via -device loader options
Reboot the host
Mount the GPU to the VM and boot it up