Of course I spoke too soon, on T3.13/Q2.0/B4.15 I now hit an FPU issue.
That builds up to a kernel stack crash (recursive)
[ 2.394255] Bad FPU state detected at fpu__clear+0x6b/0xd0, reinitializing
FPU registers.
[...]
BUG: stack guard page was hit at (ptrval) (stack is (ptrval)..
(ptrval))
That is again elated to MSR handling.
So disabling a few but keeping MDS as needed for this test helps:
<cpu mode='custom' match='exact'>
<model fallback='allow'>kvm64</model>
<feature policy='require' name='ssbd'/>
<feature policy='require' name='md-clear'/>
<feature policy='require' name='pdpe1gb'/>
<feature policy='require' name='pcid'/>
</cpu>
You have not really tested with 3.13 at the LVL1 as far as I read your updates.
I'm expecting that even 3.13 -> 4.4 already has quite some nested fixes that
made this "better but not perfect" - so you haven't seen it.
Have I already said that nested KVM on x86 can be unreliable?
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https://bugs.launchpad.net/bugs/1829555
Title:
nested virtualization w/first level trusty guests has odd MDS behavior
Status in linux package in Ubuntu:
Confirmed
Status in qemu package in Ubuntu:
New
Bug description:
When nested kvm virtualization is used (with host-passthrough), if the
first level guest is a trusty vm, odd behavior is seen in the second
level guest:
host os:
disco/5.0.0-15.16-generic/qemu 1:3.1+dfsg-2ubuntu3.1
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT vulnerable
1st level vm:
trusty/4.4.0-148.174~14.04.1-generic/qemu 2.0.0+dfsg-2ubuntu1.46
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT Host state unknown
2nd level vm:
bionic/4.15.0-50.54-generic
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Not affected
This behavior is not seen when the first level guest is a xenial or
bionic vm (same bare metal hardware):
1st level vm:
bionic/4.15.0-50.54-generic/qemu 1:2.11+dfsg-1ubuntu7.13
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT Host state unknown
2nd level vm:
bionic/4.15.0-50.54-generic
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT Host state unknown
and:
1st level vm:
xenial/4.4.0-148.174-generic/qemu 1:2.5+dfsg-5ubuntu10.39
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT Host state unknown
2nd level vm:
bionic/4.15.0-50.54-generic
contents of /sys/devices/system/cpu/vulnerabilities/mds:
Mitigation: Clear CPU buffers; SMT Host state unknown
It's not clear whether this is an issue with linux/kvm or qemu in trusty.
---
ApportVersion: 2.14.1-0ubuntu3.29
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/controlC0: ubuntu 2239 F.... pulseaudio
DistroRelease: Ubuntu 14.04
HibernationDevice: RESUME=UUID=4fa9460d-7ed4-49db-8e22-86a5107d0062
InstallationDate: Installed on 2019-02-14 (92 days ago)
InstallationMedia: Ubuntu 14.04.5 LTS "Trusty Tahr" - Release amd64 (20160803)
Lsusb:
Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
Package: qemu 2.0.0+dfsg-2ubuntu1.46
PackageArchitecture: amd64
ProcEnviron:
TERM=screen
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
ProcFB: 0 qxldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-148-generic
root=UUID=9a35107e-83fa-4010-81e1-235a4ea14fe6 ro quiet splash vt.handoff=7
ProcVersionSignature: User Name 4.4.0-148.174~14.04.1-generic 4.4.177
RelatedPackageVersions:
linux-restricted-modules-4.4.0-148-generic N/A
linux-backports-modules-4.4.0-148-generic N/A
linux-firmware 1.127.24
RfKill:
Tags: trusty trusty
Uname: Linux 4.4.0-148-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip libvirtd lpadmin plugdev sambashare sudo
_MarkForUpload: True
dmi.bios.date: 04/01/2014
dmi.bios.vendor: SeaBIOS
dmi.bios.version: 1.12.0-1
dmi.chassis.type: 1
dmi.chassis.vendor: QEMU
dmi.chassis.version: pc-i440fx-bionic
dmi.modalias:
dmi:bvnSeaBIOS:bvr1.12.0-1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-bionic:cvnQEMU:ct1:cvrpc-i440fx-bionic:
dmi.product.name: Standard PC (i440FX + PIIX, 1996)
dmi.product.version: pc-i440fx-bionic
dmi.sys.vendor: QEMU
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