As previously reported, many users were having issues with VFIO on the 5.1 kernel series, and those issues have persisted or worsened in kernel 5.2. Users report outright crashes and VMs refusing to boot, usually accompanied by KMODE_EXPECTION_NOT_HANDLED errors.
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What Can You Do About Kernel 5.2?
Currently, there isn’t any known workaround for these issues without rolling back to kernel version 5.0 or earlier, so right now we recommend installing the LTS branch and calling it a day. While the cause of these issues is still unknown, several users have reported that applying a set of patches that will be landing in 5.3 may fix the issue. Unfortunately for those with the newest AMD cards running on their host machines, this may stop them from using VFIO entirely until the problem is resolved because the LTS kernel will have less stable support for many newer AMD GPUs.
This development is somewhat disappointing, as the attention paid to kvm support seems to be dropping off in new kernel branches. The prospect of running a host on mainline, at least for now, is becoming less and less viable, even if the newer kernel is needed for hardware support.
If you’re interested in trying the workaround patches, they are as follows:
- [PATCH] Revert “kvm: x86: Use task structs fpu field for user”
- [PATCH 1/2] KVM: X86: Fix fpu state crash in kvm guest
- [PATCH 2/2] KVM: X86: Dynamically allocate user_fpu
Special thanks to VFIO discord user tet for finding these and testing them for the community.
These patches may need to be applied in addition to the ACS override, but that should be as simple as adding them in conjunction with it, since you’re patching your kernel anyway.
We’ll keep following this situation as it develops, and hopefully it will be fixed as we make our way into kernel 5.3, but we recommend users on a distro that follows the mainline branch switch to LTS for the time being.
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