NMI watchdog: BUG: soft lockup on Guest upon boot (KVM)
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
The Ubuntu-power-systems project |
Fix Released
|
Critical
|
Canonical Kernel Team | ||
linux (Ubuntu) |
Fix Released
|
Critical
|
Unassigned | ||
Xenial |
Fix Released
|
Critical
|
Unassigned |
Bug Description
== SRU Justification ==
Xenial does not include the patch:
"KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread",
which is commit 88b02cf97bb7 in the upstream Linux kernel repository. The
symptom of not having this patch is that guests running with threads > 1
(that is, in SMT2, SMT4 or SMT8 mode) can give spurious soft-lockup messages
when they are not in fact locked up, if the guest kernel uses the VTB
(virtual timebase) register in its softlockup detector code.
IBM provided this backport of commit 88b02cf97bb7.
== Fix ==
commit 88b02cf97bb7e74
Author: Paul Mackerras <email address hidden>
Date: Thu Sep 15 13:42:52 2016 +1000
KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread
== Regression Potential ==
This patch is specific to powerpc. It was provided by and tested by IBM.
Environment:
Host OS: Ubuntu 16.04 (4.4.0-97-generic)
Guest OS: Ubuntu 16.04
Host is running NovaLink and GPFS. Guest gets filesystem from gpfs cluster.
Issue:
While booting the guest OS went into recovery. dmesg shows CPU soft lockup. This issue is easily recreatable when multiple VMs (about 10) are being started simultaneously.
.......
- Paul Mackerras <email address hidden> - 2017-10-24 00:42:25 ==
Looking at kernel sources:
The Ubuntu host kernel (4.4.0-97) does not include the patch "KVM: PPC: Book3S: Treat VTB as a per-subcore register, not per-thread", which is commit 88b02cf97bb7 in the upstream Linux kernel repository. The symptom of not having this patch is that guests running with threads > 1 (that is, in SMT2, SMT4 or SMT8 mode) can give spurious soft-lockup messages when they are not in fact locked up, if the guest kernel uses the VTB (virtual timebase) register in its softlockup detector code.
This is a backport of commit 88b02cf97bb7 from the upstream Linux kernel repository to the Ubuntu 4.4 kernel. It is the fix for the problem of seeing spurious soft lockup messages in guests running in an SMT mode greater than 1.
These tests were run on a system with 20 cores. Each VM had 1 core and 4 threads (SMT=4).
It is working very well with this patch
CVE References
affects: | kernel-package (Ubuntu) → linux (Ubuntu) |
Changed in ubuntu-power-systems: | |
importance: | Undecided → Critical |
assignee: | nobody → Canonical Kernel Team (canonical-kernel-team) |
Changed in ubuntu-power-systems: | |
status: | New → Triaged |
Changed in linux (Ubuntu Xenial): | |
status: | New → In Progress |
importance: | Undecided → Critical |
assignee: | nobody → Joseph Salisbury (jsalisbury) |
Changed in linux (Ubuntu): | |
assignee: | Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) → Joseph Salisbury (jsalisbury) |
status: | Triaged → In Progress |
Changed in ubuntu-power-systems: | |
status: | Triaged → In Progress |
description: | updated |
tags: | added: triage-g |
Changed in linux (Ubuntu Xenial): | |
status: | In Progress → Fix Committed |
Changed in ubuntu-power-systems: | |
status: | In Progress → Fix Committed |
Changed in linux (Ubuntu): | |
status: | Fix Committed → Fix Released |
Changed in ubuntu-power-systems: | |
status: | Fix Committed → Fix Released |
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