Posts made by andSmv

Hello, I'm honestly don't know how Citrix vGPU stuff works, but couple of thoughts on this topic:

If I understand correctly, you say Nvidia use VFIO Linux framework to enable mediated devices which can be exported to guest. The VFIO framework isn't supported by XEN, as VFIO need the presense of IOMMU device managed by IOMMU Linux kernel driver. And XEN doesn't proide/virtualize IOMMU access to dom0 (XEN manages IOMMU by itself, but doesn't offer such access to guests)

Bascally to export SR-IOV virtual function to guest with XEN you don't have to use VFIO, you can just assign the virtual function PCI "bdf" id to guest and normally the guest should see this device.

From what I understand Nvidia user-mode toolstack (scripts & binaries) doesn't JUST create SR-IOV virtual functions, but want to access VFIO/MDEV framework, so all this thing fails.

So may be, you can check if you there's some options with Nvidia tools to just create SR-IOV functions, OR try to run VFIO in "no-iommu" mode (no IOMMU presence in Linux kernel required)

BTW, we working on some project where we are intending to use VFIO with dom0, and so we're implementing the IOMMU driver in dom0 kernel, so it would be interesting to know in the future, if this can help with your case.

Hope this help

It's obviously is not exluded that the issue is related to the memory footprint. Moreover the first warning "complains" about failure on memory allocation. (I suppose that the "receiver" node has enough memory to host the VM).

Normally XEN hasn't limitations on Live Migration 24GB VM. So, it's difficult to say what's the issue here. But clearly there's a possibity that this is a bug in XEN/toolstack... Memory fragmentation on the receiver" node can be an issue too.

You can probably run some different configurations to try to pinpoint this issue.
May be for the start try to migrate a VM when no other VMs are running on the "receiver" node. Also try to migrate a VM with no network connections (as the issue seems to be related to network backend status changes)....

Yeah, The HW problem seems to be a good guess.

The track that we can follow here is xen_mc_flush kernel function which raises a warning when a multicall (hypercall wrapper) fails. The interesting thing here would be to take a look at XEN traces. You can type xl dmesg in dom0 to see if XEN tells something more (if it isn't happy on some reason)

Hmmm, there's two poblems here (page alloc failure warning and NULL pointer BUG) in context of xenwatch kernel thread and basically both of them happenning when configuring XEN network frontend/backend communications.

Normally this isn't related to memory footprint of the VM, but rather to XEN frontend/backend xenbus communication framework. Does the bugs desappear when you reduce the memory size for the VM and when all others params/environnement are the same?

@jjgg Here's the link to xen.gz.

You need to put it in your /boot folder (backup your existent file!) and make sure your grub.cfg is pointing to it.

But first: Backup all you want to backup! The patch is totally untested and doesn't apply as is (so I needed to adapt it). Normally not such a big deal and should not do no harm, but... you never know.

I'm also not sure that the issue would be fixed. We unfortunatelly do not have Coral TPU device at Vates, so we can't do the more deep analysis on this. The guy who wrote this patch tried to fix other device.

@exime - this is 4.13.5 XCP-ng patched xen, so there's chances it wouldn't work for you (from what I saw you're running 4.13.4 xen)

Anyway, if we have good news, we'll find the way to fix it for everybody.

@jjgg Thank you. Yes the same problem - ept violation.. Look, I'll try to figure out what we can do here. There's a patch that comes from Qubes OS guys that normally shold fix the MSI-x PBA issue (not sure that this is the good fix, but still... worth trying) This patch applies on recent Xen and wasn't accepted yet. I will take a look if it can be easily backported to XCP-ng Xen and come back to you.

@jjgg Can you please also post XEN traces after the VM is stopped.
(either in hypervisor.log or just type xl dmesg (under root account in your dom0)

@ashceryth XCP-ng is based on Xen 4.13, so I'm quite sure it doesn't handle Intel Hybrid architecture. I'm not even sure there's ongoing efforts on this support in Xen Project Community.

Moreover, after a very quick check, I didn't see the trace of ARM big.LITTLE support in recent XEN.

I think this kind of features needs the profound analysis how exactly is to be mapped on hypervisor based platforms. And I think the response is not obvious at all.

@jevan223 Well, if you confirm it worked well on i440fx that probably the hypothesis is wrong. Whas it kvm-qemu virtualization?

@jevan223 This is not about the real hardware. This is about the emulated chipset offered by QEMU to HVM guests (which is the case with Windows VM)

QEMU actually emulates 2 chipset to its guests

• i440fx: basic PCI bus with CAM access

• Q35: enhanced PCI bus with ECAM access (and thus access to PCI-e capabiliites).

The problem is that Q35 is not supported by xen-dependant parts in QEMU code, so only i440fx is emulated for XEN HVM guests. We are actually working to enable Q35 in XEN, but this is a work in progress.

Well, this is a hypothesis which needs to be confirmed, but by the look of a lspci output, there's a good chance that's the reason

@logical-systems I will check which Xen version the patches are easily applied and If you want I could give you a hand (if needed) to build and install your builded XEN, so you can test if this resolve your issue.

Unfortunatly we don't have the related HW (Coral TPU) to test it by ourselves.

UPDATE: the both patches apply to xen 4.17 (tag RELEASE-4.17.0)

Yes. Some of the PCI capabilities are beyond the "standard" PCI configuration space of 256 bytes per BDF (PCI device). And unfortunatly the "enhanced" configuration access method is not provided yet (it's ongoing work) for HVM guests by XEN. It would require from QEMU (xen related part) the chipset emulation which offers an access to such method, such as Q35.

Very probably, windows drivers for these devices are not happy to not access these fields, so this is potentially the reason of malfunctionning for these devices.

The good way to confirm this would be to try to passthrough these devices to Linux guests, so we could possibly add some extended traces. And possibly passthrough these devices to PVH Linux guest and see how they are handled (PVH guest do not use QEMU for PCI bus emulation)

@jevan223 can you please provide a lspci -vvv output (in dom0) ?

Hmm, at first glance looks to me as a real use case for q35 chipset emulation support on XEN ?

Hello, sorry for late response (just discovered the topic)

With regards of Marek patches, I'm actually think it can worth a try (at least the patch seems to treat the problem where MSI-x PBA page is shared with other regs of the device), but there's some cons too:

• the patches are quite new (doesn't seems to be integrated yet).
• the patches can be applied to more recent Xen (not XCP-ng Xen), and even we could probably backport them, it potentially will require some significant work
• we are not 100% sure it's the issue (or the only issue)

So If this is a must have, we can go and do some digging to make it work (but still in the scope of "exeperimental" platform, not the production platform)

Hello @bogikornel

The Intel_errata_workarounds and probe_c3_errata routines are executed unconditionally (there's no boot parameter to disable these checks)

The only way through would be to recompile your Xen. I'm not sure that this is a good idea because Intel documentation talks about Unpredictable System Behaviour.

If that is really what you need, I can help you with this (or do this for you), so let me know...

Hello @phipra

You're right, this obviously can be a bug in Citrix drivers.

To confirm this hypothesis you can desinstall Citrix Tools. There will be some impact on performances as you will run on emulated hardware and not paravirtualized, but normally this should work.

BACKUP all important data (snapshot would be a good idea) and follow this procedure https://xcp-ng.org/docs/guests.html#upgrade-from-citrix-xenserver-client-tools to desinstall and clean-up all Citrix add-on software. You would probably want to stop at step 5 if you're not using the scripts and proceeding with manual desinstall.

Hope this helps

Hello @phipra,
Sorry for late response (didn't see this earlier)

Well, this is the tricky one.

The triple fault could normally be two things:

• heavy memory corruption (the IDT was corrupted)
• the normal reboot (if ACPI reboot is not available)

My question is - can this Windows reboot be a planified Windows reboot (for example related with Windows update mechanism, or something like that ....)?

It can be obviously be a memory corruption (and possibly done by citrix-vm-tools drivers), but it'll be VERY hard to debug this from a memory dump (and actually AFAIK xen doesn't provide a guest memory dump).

My suggestions would be - try to enable/disable some Windows Services (disable the Update?) to see if there's some changes.

Sorry for this very poor insight, but this is related to my rather poor knowledge about Windows OS.

Hello @exime,

Here we have the EPT violation (write access to the r-x page) at 0x3fff2046. This address is tagged as an MMIO address, so very probably belongs to the device you're trying to passthrough.

Normally this has nothing to do with the 0x46xxx range (where MSI-X caps are pointing)? But the fact that there's some hacking in there make me think that Google engs also did some hacking all the place around.

Can you please while starting a native guest (or in dom0 before the passthrough) give a PCI dump for your device

lspci -vvv -s $YOUR_DEV_BDF

YOUR_DEV_BDF is your device PCI id (ex: 00:1:0)

Thank you for all these links! I will look through them (need some time though)