Based on the technical information so far provided by the Debian community in this report and in the related bug #991967, I consider this bug closed. For me it is fixed. I found the solution for it on my hardware and shared it with the Debian community. I do not care if the official Debian developers implement my suggestion or not. I will not run Debian's version which is really a mix of Xen-4.14 stable and Xen-4.16 unstable. Instead I will run the version with the patch I suggested in this bug report, and AFAICT I will have a more stable and bug-free version of Xen than anyone who runs the current so-called stable version of Xen for Debian.
Since the information about this bug is scattered in various places in the this bug report and in #991967, I will say this bug concerned the following hardware/software configuration: Motherboard/CPU: ASRock B85M Pro4, BIOS P2.50 12/11/2015, with a Haswell CPU (core i5-4590S) Boot system: EFI, not using secure boot, booting xen hypervisor and dom0 bullseye with grub-efi package for bullseye, and it boots the xen-4.14-amd64.gz file, not the xen-4.14-amd64.efi file. Init system: systemd Xen domain type: Domain 0 Linux Kernel Versions: all Linux kernel versions of both buster and bullseye running as a dom0 I tested exhibit the bug, but no Debian stable Linux kernel version since 4.19.0-16 running as a dom0 exhibited the bug with the Xen hypervisor for buster. If you are experiencing the symptoms described in this bug report, the solution I proposed for Debian in both this bug report and in #991976 might fix the bug if your hardware and software configuration is similar to what I have described above. However, to fix it you will have to test it yourself, and that would involve building the Xen package for bullseye from source, unless and until Debian decides to implement the fix I proposed in my original bug report. if you use BIOS boot and/or sysv-init instead of EFI boot and/or systemd, it is likely the fix I have described here will not fix the bug, and also if you have a newer intel cpu or an amd cpu the fix might not work on your hardware, but it might work if you use EFI and systemd in those latter cases. If you try the solution I proposed here and it does not solve your issue, I would suggest that you look at #991976 before reporting a new bug. I will not take action to close this bug; that is up to the Debian developers to decide. Instead, I will select this message to be a summary of the bug. Happy computing on Debian, Chuck Zmudzinski