Chuck Zmudzinski
2022-Feb-07 17:16 UTC
[Pkg-xen-devel] Bug#988333: : VGA Intel IGD Passthrough to Debian Xen HVM DomUs not working
On 10/23/2021 11:11 AM, Hans van Kranenburg wrote:> Hi! > > On 10/19/21 5:44 AM, Chuck Zmudzinski wrote: > >> I will continue to investigate this issue and try to bisect the problem >> as it recurs in Dom0 for some version of Xen > 4.4 and <= 4.14. It >> will obviously take some time since there are so many differences >> between Xen 4.4 and 4.14. > If you can make progress on that, and find an actual commit that changes > the behavior, then we're probably at 95% towards finding a cause and > solution. :) That'd be great.In more recent tests, I have identified the regression occurs in Dom0 for some version of Xen > 4.4 and < Xen 4.5.0. In these old versions of Xen, only the qemu traditional device model supports IGD passthrough, so in these tests I am investigating the regression that causes the crash in the Intel i915 drm kernel module in the HVM, rather than the regression that causes problems with assigning IRQs correctly, which as discussed earlier occurs only with the upstream device model [1]. I am continuing to narrow down the problem with the Intel i915 kernel module crash since now I have started to build and test the Xen 4.5-unstable packages for jessie with the traditional qemu device model. When the upstream Xen 4.5 branch was first created, the bug was not present yet since that was essentially a 4.4 release candidate, but it was present by the time Xen 4.5.0 was released. I will hopefully be able to find the commit along the development of the Xen 4.5 branch that introduced the crash in the i915 drm kernel driver in the bullseye HVM DomU. It will take some time because there are hundreds of commits from the start of the Xen 4.5 branch to the release of Xen 4.5.0, and since these are unstable pre-release candidate builds of upstream Xen 4.5, it will not always be easy or even possible to build and test them all. If we can identify the cause of the i915 crash in Xen 4.5, then we can decide if it is possible to fix it in modern versions of Xen.> > A possible time-saver that I can recommend is to send a post to the > upstream xen-users list [0] about this already. Like "Hi all, I'm > starting a HVM Linux domU with Linux 5.10.70 on a Xen 4.14.3 system with > also 5.10.70 dom0 kernel, with this and this domU config file. It fails > to start, this is the xl -vvv create output, and this error (the irq > stuff) appears in the dom0 kernel log.". Try to keep it simple and not > too long initially, without the surrounding stories, to increase chance > of it being fully read.I did send a message to the list last October [2], but did not get a helpful reply, so that is why I am bisecting this problem myself. If we can fix this problem with the Intel i915 drm kernel module, then it is likely another bug against src:qemu (instead of src:xen) to fix the problem with handling IRQs properly with the bullseye upstream qemu device model will need to be opened and investigated to allow IGD passthrough to work using an unmodified bullseye Dom0, but I will only do that if we can fix the bug here in src:xen first.> Have fun, > HansI am having fun! Thanks, Chuck> > [0] https://lists.xenproject.org/mailman/listinfo/xen-users >[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=988333#36 [2] https://lists.xenproject.org/archives/html/xen-users/2021-10/msg00041.html