Passthrough not working with OpenBSD nor NetBSD

John Baldwin jhb at
Thu Aug 9 17:30:08 UTC 2018

They may implement INTx interrupts for pass-through perhaps.  INTx are a
lot bigger pain to emulate since there isn't a standard way in PCI to
determine if an interrupt is pending (and you need that to simulate a
level-triggered interrupt like INTx).  I think very recent revisions of
PCI did add a new bit to test that in the PCI status register, but it is
in a new enough version of PCI that any compliant devices would also support
MSI anyway.

On 8/9/18 10:07 AM, Farid Joubbi wrote:
> How does KVM and VMware solve that?
> I haven't tried PCI passthrough with them, but I assume that it works..?
> On Thu, Aug 9, 2018, 18:24 John Baldwin <jhb at <mailto:jhb at>> wrote:
>     On 8/8/18 11:08 AM, Farid Joubbi wrote:
>     > That's what I also thought, but it's not anything I can force it to do, is it? Isn't it supposed to detect the MSI interrupt compatibility automatically?
>     Apparently Open/Net always try to setup INTx before trying MSI even if they
>     won't use INTx per the commit log in revision 280725.  We could perhaps try
>     to provide a "fake" INTx interrupt that doesn't work, but I'll have to think
>     about how to implement that.
>     -- 
>     John Baldwin

John Baldwin

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