[Xen-users] Xen 4.8 with Intel Integrated Graphics - DMA Error (PTE Read access not set) errors

[Stephen Oberholtzer]

Xen 4.8.4-pre
Dom0 = Debian Testing (Buster)

After upgrading my system (new motherboard+CPU, new Xen version), I got
floods of DMA errors in Xen and Dom0.

This appears in `xl dmesg`:
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set
(XEN) printk: 742 messages suppressed.
(XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault addr
3b63651000, iommu reg = ffff82c000201000
(XEN) printk: 749 messages suppressed.

This appears in `dmesg` on Dom0:

[ 31.298250] [drm:gen8_irq_handler [i915]] *ERROR* Fault errors on pipe
A: 0x00000080

(This exact message is generated about 100 times per second.)

Based on my searches, I added `iommu=no-igfx` to the Xen command line, and
the problem seems to have gone away.
According to
https://xenbits.xen.org/docs/unstable/misc/xen-command-line.html, if
`no-igfx` fixes anything, I should file a bug reporting the problem -- but
should I report it to Xen, or my BIOS vendor? I strongly suspect the
latter, but I don't know what I should tell them.