Re: i915 dma faults on Xen

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.10.2020 11:58, Roger Pau Monné wrote:
> On Fri, Oct 16, 2020 at 12:23:22PM -0400, Jason Andryuk wrote:
>> The RMRRs are:
>> (XEN) [VT-D]Host address width 39
>> (XEN) [VT-D]found ACPI_DMAR_DRHD:
>> (XEN) [VT-D]  dmaru->address = fed90000
>> (XEN) [VT-D]drhd->address = fed90000 iommu->reg = ffff82c00021d000
>> (XEN) [VT-D]cap = 1c0000c40660462 ecap = 19e2ff0505e
>> (XEN) [VT-D] endpoint: 0000:00:02.0
>> (XEN) [VT-D]found ACPI_DMAR_DRHD:
>> (XEN) [VT-D]  dmaru->address = fed91000
>> (XEN) [VT-D]drhd->address = fed91000 iommu->reg = ffff82c00021f000
>> (XEN) [VT-D]cap = d2008c40660462 ecap = f050da
>> (XEN) [VT-D] IOAPIC: 0000:00:1e.7
>> (XEN) [VT-D] MSI HPET: 0000:00:1e.6
>> (XEN) [VT-D]  flags: INCLUDE_ALL
>> (XEN) [VT-D]found ACPI_DMAR_RMRR:
>> (XEN) [VT-D] endpoint: 0000:00:14.0
>> (XEN) [VT-D]dmar.c:615:   RMRR region: base_addr 78863000 end_addr 78882fff
>> (XEN) [VT-D]found ACPI_DMAR_RMRR:
>> (XEN) [VT-D] endpoint: 0000:00:02.0
>> (XEN) [VT-D]dmar.c:615:   RMRR region: base_addr 7d000000 end_addr 7f7fffff
>> (XEN) [VT-D]found ACPI_DMAR_RMRR:
>> (XEN) [VT-D] endpoint: 0000:00:16.7
>> (XEN) [VT-D]dmar.c:581:  Non-existent device (0000:00:16.7) is
>> reported in RMRR (78907000, 78986fff)'s scope!
>> (XEN) [VT-D]dmar.c:596:   Ignore the RMRR (78907000, 78986fff) due to
> 
> This is also part of a reserved region, so should be added to the
> iommu page tables anyway regardless of this message.

Could you clarify why you think so? RMRRs are tied to devices, so
if a device in reality doesn't exist (and no other one uses the
same range), I don't see why an IOMMU mapping would be needed
(unless to work around some related firmware bug). Plus aiui none
of the IOMMU faults actually report this range as having got
accessed.

Jan