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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



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


Now I have some questions:

 - is disabling VT-d in the BIOS settings equivalent to booting with
   intel_iommu=off kernel parameter?

 - 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?

 - does this additional information help in understanding the issue
   and, perhaps, in fixing it?


Please let me know, thanks for your kind assistance!


-- 
 http://www.inventati.org/frx/
 There's not a second to spare! To the laboratory!
..................................................... Francesco Poli .
 GnuPG key fpr == CA01 1147 9CD2 EFDF FB82  3925 3E1C 27E1 1F69 BFFE

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