sbonazzo created OVIRT-2545:
-------------------------------
Summary: Fwd: [ovirt-users] Backport KVM bug fix for nested KVM in
ESXi and Hyper-V
Key: OVIRT-2545
URL: https://ovirt-jira.atlassian.net/browse/OVIRT-2545
Project: oVirt - virtualization made easy
Issue Type: By-EMAIL
Reporter: sbonazzo
Assignee: infra
Opening a ticket because looks like the forwarded email doesn't show up on
list archives at
https://lists.ovirt.org/archives/list/[email protected]/2018/10/
Marc can you please check?
---------- Forwarded message ---------
From: Gianluca Cecchi <[email protected]>
Date: mar 16 ott 2018 alle ore 12:57
Subject: [ovirt-users] Backport KVM bug fix for nested KVM in ESXi and
Hyper-V
To: users <[email protected]>
Hello,
I send a dedicated subject message on this topic.
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
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Red Hat EMEA <https://www.redhat.com/>
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