From: Fiona Ebner <f.ebner@proxmox.com>
To: pve-devel@lists.proxmox.com
Cc: niels@rootnet.nl
Subject: Re: qm showcmd shows incorrect PCI device address
Date: Wed, 29 Jul 2026 12:25:08 +0200 [thread overview]
Message-ID: <78a32cca-3e53-4418-82cf-7fabf83d8c32@proxmox.com> (raw)
In-Reply-To: <2821634225-1232228@mx.rootnet.nl>
Just for the record, this was already answered in the forum:
https://forum.proxmox.com/threads/qm-showcmd-shows-incorrect-pci-device-address.185370/
And a bugzilla issue was opened afterwards:
https://bugzilla.proxmox.com/show_bug.cgi?id=7857
Best Regards,
Fiona
Am 28.07.26 um 3:07 PM schrieb Niels Hendriks:
> Hello,
>
>
> As is probably known, there are quite a few issues with reliable PCI passthrough.
> We've been able to get PCI passthrough working well, with one caveat: if GPU 1 is assigned to VM A, and is then re-assigned to VM B, it sometimes does not come up properly. The error we get within the VM is that the GPU has "fallen off the bus".
> We have tried many things, but the only way to reliably resolve this is to run a pre-start hookscript that removes the PCI device and re-discovers it.
>
>
> We use a resource mapping to simplify the VM configs, and to determine which device has to be removed and re-discovered, we use the "qm showcmd <vmid>" command.
> However, we found out this does not work reliably. the showcmd command actually always appears to show the first PCI address of the resource mapping. And if >1 GPU is present it would show the first addresses of the GPU resource mapping.
>
>
> This appears to be caused by this change: https://www.mail-archive.com/pve-devel@lists.proxmox.com/msg27318.html
>
>
> This appears to be an intended change, but I don't know if my usecase was considered when the change was made.
> Is there a different way to determine the PCI address(es) that will be used when starting a VM using a resource mapping? Or is this actually an unintended side-effect?
>
>
> Alternatively we could remove the resource mapping of course, but if possible we would like to avoid doing that (for a simpler VM configuration)
>
>
> Thank you
> Niels Hendriks
>
> __________________________________________________________
> RootNet B.V.
>
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prev parent reply other threads:[~2026-07-29 10:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-28 10:18 qm showcmd shows incorrect PCI device address Niels Hendriks
2026-07-29 10:25 ` Fiona Ebner [this message]
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