Package: release-notes As of Linux kernel version 5.9, support for 32-bit Xen guests running in PV mode was dropped:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a13f2ef168cb2a033a284eb841bcc481ffbc90cf Since bullseye comes with a 5.10 kernel, a 32-bit Xen PV guest may be running fine under buster, do a dist-upgrade to bullseye which completes without issue and then on reboot the kernel can't be booted. This has just happened to two of my customers, once last night and once this morning, despite many years of us advising customers to switch to 64-bit and/or PVH mode. These 32-bit Xen guests can continue to run as 32-bit if they are run as PVH mode guests instead, or they can continue to run as 64-bit PV mode guests (with 32-bit userland) if the guest admin installs the amd64 kernel as per: https://wiki.debian.org/CrossGrading I think this issue should be mentioned in the i386 release notes in the upgrading from buster part. I am happy to propose some text for that if it is agreed. Thanks, Andy