RE: [PATCH v3] iommu/vt-d: Disable IOMMU by default on Lenovo ThinkPad P50s

> From: Oliver Lin <[email protected]>
> Sent: Monday, July 27, 2026 12:49 PM
> 
> On 27/07/2026 12:03, Tian, Kevin wrote:
> > If it's confirmed to be a hardware issue, it should be (or will be)
> documented
> > as an VT-d erratum. Then a quirk could be added accordingly.
> >
> > If Lenovo confirms to be a firmware issue, then they should release a new
> > firmware version to fix it. It doesn't justify a quirk in iommu driver.
> >
> > and it is not about a policy "whether this issue should be *treated* as...".
> > It needs a root cause first.
> 
> 
> Hi Kevin,
> 
> I performed additional investigation on the DMA fault.
> 
> With intel_iommu enabled:
> 
> DMAR: [DMA Read NO_PASID] Request device [0000:00:12.4] fault addr
> 0xb7fff000 [fault reason 0x02] Present bit in context entry is clear
> 
> However, requester ID 0000:00:12.4 does not appear in PCI enumeration:
> 
> - `lspci -nn -s 00:12.4` returns no output
> - `lspci -xxxx -s 00:12.0` through `00:12.4` all return no device
> - `/sys/bus/pci/devices/` contains no matching entry
> 
> I also checked the firmware-provided ACPI DMAR table. It contains scopes
> for 00:02.0 and 00:14.0, but no scope for 00:12.4.
> 
> Could this requester ID correspond to an internal platform device, or
> does this suggest a firmware/platform issue?
> 

from a hidden device? no idea... You should report this issue to Lenovo
first as only they know the detail of this platform.