Bug#1112627: linux-image-6.16.3+deb14-amd64: Intel audio no longer works: DMAR: [DMA Write NO_PASID] Request device [00:1b.0] ... non-zero reserved fields in PTE
Hi Francesco
On Wed, Nov 05, 2025 at 11:52:55PM +0100, Francesco Poli wrote:
> On Sun, 26 Oct 2025 23:36:29 +0100 Francesco Poli wrote:
>
> [...]
> > By the way, an important question: booting
> > linux-image-6.16.12+deb14+1-amd64/6.16.12-2 with intel_iommu=off makes
> > audio work, apparently.
> > Is adding this kernel boot parameter a possible (temporary) workaround?
> >
> > On Sat, 25 Oct 2025 16:49:26 +0200 Salvatore Bonaccorso wrote:
> [...]
> > > The second thing we were suggsting: In the boot log the BIOS version
> > > shown is from 2014. Double check if there is an update available. If
> > > so please upgrade to the latest available one, which might have fixed
> > > underlying issue.
> >
> > I'll try and check whether there is a BIOS update available... although
> > flashing this update (if any is indeed available) won't necessarily be
> > an easy and trouble-free process... :-(
>
> Important update: I flashed the latest BIOS available for the
> motherboard (ASRock Z97 Extreme6). This way, I switched from version
> P1.60 (year 2014) to version P2.80 (year 2018), as can be seen from the
> BIOS download [page].
>
> [page]: <https://www.asrock.com/MB/Intel/Z97%20Extreme6/index.asp#BIOS>
>
> I booted linux-image-6.16.12+deb14+1-amd64/6.16.12-2 and the issue
> seemed to have gone away!
>
> Then I happily rebooted and tweaked the few BIOS settings I had
> customized before the BIOS update (as documented by ASRock, all
> settings were reset to their defaults during the BIOS update).
> I booted linux-image-6.16.12+deb14+1-amd64/6.16.12-2 again, and,
> surprise!, the issue was back... :-(
>
> After a few tests, I figured out which setting makes the issue
> appear/disappear:
>
> * if I enable VT-d, audio fails to work
>
> * if I disable VT-d, audio works correctly
Yes BIOS flashing/updating are not fun :(
> Now I have some questions:
>
> - is disabling VT-d in the BIOS settings equivalent to booting with
> intel_iommu=off kernel parameter?
Yes, this result is equivalent.
> - I thought that enabling VT-d was needed for QEMU in KVM mode, but I
> cannot verify it (starting 'kvm' seems to work, without any visible
> complaint): could you please tell me what I am missing, by disabling
> VT-d?
It depends on which use cases you have for the VMs. Do you need to
passh through hardware? Do you use nested virtualization?
> - does this additional information help in understanding the issue
> and, perhaps, in fixing it?
That is still the harder part :(. We will have another meeting on
wednesday and this bug will likely (unless we run out of time) be on
the agenda/table again.
We see more IOMMU related failures recently (when old HW is involved),
so this might indeed be the way forward, tbh. But we will see tomorrow
is someone has other input on the topic.
Regards,
Salvatore
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