Re: [Qemu-devel] Virtual IOMMU is working for Windows VM?

[Jintack Lim <jintack@cs.columbia.edu>]

On Mon, Oct 22, 2018 at 5:27 AM Peter Xu <peterx@redhat.com> wrote:
>
> On Mon, Oct 22, 2018 at 12:22:02AM -0400, Jintack Lim wrote:
> > Hi,
> >
> > I wonder if vIOMMU is working for Windows VM?
> >
> > I tried it with v2.11.0, but it didn't seem to work. I assume that seaBIOS
> > sets IOMMU on by default as is the case when I launched a Linux VM. But I
> > might be missing something. Can somebody shed some light on it?
>
> Hi, Jintack,
>

Thanks Peter,

> I think at least the latest QEMU should work for Windows, but I don't
> really run Windows that frequently.
>
> What is the error you've encountered?  Have you tried the latest QEMU,
> or switching Windows versions to try?

I ran Windows commands in Windows Powershell like below. Well, I guess
this is not the best way to check IOMMU presence, but couldn't find a
better way to do it.

$ (Get-VMHost).IovSupport
false
$ (Get-VMHost).IovSupportReasons
The chipset on the system does not do DMA remapping, ...

I just tried QEMU v3.0.0, but I see the same symptom. I'm using
Windows server 2016.  Unfortunately, trying another Windows version
would be hard for me at this point.

I just wonder if there's way to check if Vt-d is on in SeaBIOS?

>
> What I can remember about Windows is that Ladi had fixed a bug for
> windows-only (8991c460be, "intel_iommu: relax iq tail check on
> VTD_GCMD_QIE enable", 2017-07-03) but it should be even in 2.10 so I
> guess it's not the problem you've encountered.

I'm CCing Ladi, just in case he has some idea :)

Thanks,
Jintack

>
> Regards,
>
> --
> Peter Xu
>