On Mon, May 25, 2020 at 5:16 AM Tian, Kevin <kevin.t...@intel.com> wrote:
> > From: Jan Beulich <jbeul...@suse.com> > > Sent: Wednesday, May 20, 2020 7:11 PM > > > > On 11.05.2020 19:43, buy computer wrote: > > > I've been working on a Windows 10 HVM on a Debian 10 dom0. When I > > was first > > > trying to make the VM, I was getting IOMMU errors. I had a hard time > > > figuring out what to do about this, and finally discovered that putting > > > iommu=no-igfx in the grub stopped the errors. > > > > > > Unfortunately, without the graphics support the VM is understandably > > slow, > > > and can crash. I was also only now pointed to the page > > > <https://xenbits.xen.org/docs/unstable/misc/xen-command- > > line.html#iommu> > > > which says to report any errors that get fixed by using iommu=no-igfx. > > what is the platform and linux kernel version in this context? > > I'm not sure what you meant by 'platform', so I'll try to cover all the bases. Kernel: 4.19.0-9-amd64 GNU/Linux Debian 10.4 Lenovo E490 ThinkPad Intel Integrated Graphics 620 > > > > Thanks for the report. For context I'll quote the commit message of > > the commit introducing the option as well as the request to report > > issues fixed with it: > > > > "As we still cannot find a proper fix for this problem, this patch adds > > iommu=igfx option to control whether Intel graphics IOMMU is enabled. > > Running Xen with iommu=no-igfx is similar to running Linux with > > intel_iommu=igfx_off, which disables IOMMU for Intel GPU. This can be > > used by users to manually workaround the problem before a fix is > > available for i915 driver." > > > > This was in 2015, referencing Linux >= 3.19. I have no idea whether > > the underlying driver issue(s) has/have been fixed. The addresses > > referenced are variable enough and all within RAM, so I'd conclude > > this is not a "missing RMRR" issue. > > Variable enough but not within RAM. From E820: > > (XEN) 0000000100000000 - 0000000871800000 (usable) > > But the referenced addresses are way higher: > > (XEN) [VT-D]DMAR:[DMA Read] Request device [0000:00:02.0] fault > addr 76c615d000, iommu reg = ffff82c000a0c000 > (XEN) [VT-D]DMAR: reason 06 - PTE Read access is not set > > > > > Cc-ing the VT-d maintainer for possible insights or thoughts. > > > > Jan > > I don't have other thoughts except the weird addresses. It might be > good to add some trace in dom0's i915 driver to see whether those > addresses are intended or not. > > Thanks for the insight! I'd love to help with the trace, but I don't know how to do that. If you could point me in the right direction, I'd try to give it a shot. Thanks > Kevin > Thanks for the insight!
