[ovirt-users] Backport KVM bug fix for nested KVM in ESXi and Hyper-V

Hello, I send a dedicated subject message on this topic (second attempt because the first one seems not to be present in ovirt archive..). Also, the reply to my other related message seems not visible inside list archive page for some reason. It seems this nasty problem in nested virt using pc-i440fx-rhel7.X.0 machine type with X >= 3 impacts not only vSphere as main hypervisor for nested KVM, but other hypervisors too (Hyper-V) and other machine types too and could be due to a bug in KVM, so in the kernel, if I understood correctly. According to this link below https://bugs.launchpad.net/qemu/+bug/1636217 and its comment by Roman Kagan in June this year: " This is a KVM bug. It has been fixed in mainstream Linux in commit d391f1207067268261add0485f0f34503539c5b0 Author: Vitaly Kuznetsov <email address hidden> Date: Thu Jan 25 16:37:07 2018 +0100 x86/kvm/vmx: do not use vm-exit instruction length for fast MMIO when running nested I was investigating an issue with seabios >= 1.10 which stopped working for nested KVM on Hyper-V. The problem appears to be in handle_ept_violation() function: when we do fast mmio we need to skip the instruction so we do kvm_skip_emulated_instruction(). This, however, depends on VM_EXIT_INSTRUCTION_LEN field being set correctly in VMCS. However, this is not the case. Intel's manual doesn't mandate VM_EXIT_INSTRUCTION_LEN to be set when EPT MISCONFIG occurs. While on real hardware it was observed to be set, some hypervisors follow the spec and don't set it; we end up advancing IP with some random value. I checked with Microsoft and they confirmed they don't fill VM_EXIT_INSTRUCTION_LEN on EPT MISCONFIG. Fix the issue by doing instruction skip through emulator when running nested. Fixes: 68c3b4d1676d870f0453c31d5a52e7e65c7448ae Suggested-by: Radim Krčmář <email address hidden> Suggested-by: Paolo Bonzini <email address hidden> Signed-off-by: Vitaly Kuznetsov <email address hidden> Acked-by: Michael S. Tsirkin <email address hidden> Signed-off-by: Radim Krčmář <email address hidden> Although the commit mentions Hyper-V as L0 hypervisor, the same problem pertains to ESXi. The commit is included in v4.16. " Is it possible to backport the fix to the kernel provided by plain RHEL/CentOS hosts and/or RHVH/ovirt-ng nodes? Thanks, Gianluca