[Qemu-devel] [Bug 1665389] Re: Nested kvm guest fails to start on a emulated Westmere CPU guest under a Broadwell CPU host

[Nadav Goldin]

Hi Dave, thanks for looking into this.

> Can you clarify what the host and L1 kernels are please?

Host - 4.8.15-200.fc24.x86_64
Guest - 3.10.0-514.2.2.el7.x86_64

Results of adding the debug messages and running a simpler command(with
master again - 5dae13):

address@hidden ~]# /usr/bin/qemu-custom -s -machine pc,accel=kvm,usb=off -cpu 
Westmere
kvm_msr_entry_add: @0 index=174 value=0
kvm_msr_entry_add: @1 index=175 value=0
kvm_msr_entry_add: @2 index=176 value=0
kvm_msr_entry_add: @3 index=277 value=7040600070406
kvm_msr_entry_add: @4 index=c0000081 value=0
kvm_msr_entry_add: @5 index=c0010117 value=0
kvm_msr_entry_add: @6 index=3b value=0
kvm_msr_entry_add: @7 index=1a0 value=1
kvm_msr_entry_add: @8 index=9e value=30000
kvm_msr_entry_add: @9 index=d90 value=0
kvm_msr_entry_add: @10 index=c0000083 value=0
kvm_msr_entry_add: @11 index=c0000102 value=0
kvm_msr_entry_add: @12 index=c0000084 value=0
kvm_msr_entry_add: @13 index=c0000082 value=0
kvm_msr_entry_add: @14 index=10 value=0
kvm_msr_entry_add: @15 index=12 value=0
kvm_msr_entry_add: @16 index=11 value=0
kvm_msr_entry_add: @17 index=4b564d02 value=0
kvm_msr_entry_add: @18 index=4b564d04 value=0
kvm_msr_entry_add: @19 index=4b564d03 value=0
kvm_msr_entry_add: @20 index=2ff value=0
kvm_msr_entry_add: @21 index=250 value=0
kvm_msr_entry_add: @22 index=258 value=0
kvm_msr_entry_add: @23 index=259 value=0
kvm_msr_entry_add: @24 index=268 value=0
kvm_msr_entry_add: @25 index=269 value=0
kvm_msr_entry_add: @26 index=26a value=0
kvm_msr_entry_add: @27 index=26b value=0
kvm_msr_entry_add: @28 index=26c value=0
kvm_msr_entry_add: @29 index=26d value=0
kvm_msr_entry_add: @30 index=26e value=0
kvm_msr_entry_add: @31 index=26f value=0
kvm_msr_entry_add: @32 index=200 value=0
kvm_msr_entry_add: @33 index=201 value=0
kvm_msr_entry_add: @34 index=202 value=0
kvm_msr_entry_add: @35 index=203 value=0
kvm_msr_entry_add: @36 index=204 value=0
kvm_msr_entry_add: @37 index=205 value=0
kvm_msr_entry_add: @38 index=206 value=0
kvm_msr_entry_add: @39 index=207 value=0
kvm_msr_entry_add: @40 index=208 value=0
kvm_msr_entry_add: @41 index=209 value=0
kvm_msr_entry_add: @42 index=20a value=0
kvm_msr_entry_add: @43 index=20b value=0
kvm_msr_entry_add: @44 index=20c value=0
kvm_msr_entry_add: @45 index=20d value=0
kvm_msr_entry_add: @46 index=20e value=0
kvm_msr_entry_add: @47 index=20f value=0
kvm_msr_entry_add: @48 index=17a value=0
kvm_msr_entry_add: @49 index=17b value=ffffffffffffffff
kvm_msr_entry_add: @50 index=400 value=ffffffffffffffff
kvm_msr_entry_add: @51 index=401 value=0
kvm_msr_entry_add: @52 index=402 value=0
kvm_msr_entry_add: @53 index=403 value=0
kvm_msr_entry_add: @54 index=404 value=ffffffffffffffff
kvm_msr_entry_add: @55 index=405 value=0
kvm_msr_entry_add: @56 index=406 value=0
kvm_msr_entry_add: @57 index=407 value=0
kvm_msr_entry_add: @58 index=408 value=ffffffffffffffff
kvm_msr_entry_add: @59 index=409 value=0
kvm_msr_entry_add: @60 index=40a value=0
kvm_msr_entry_add: @61 index=40b value=0
kvm_msr_entry_add: @62 index=40c value=ffffffffffffffff
kvm_msr_entry_add: @63 index=40d value=0
kvm_msr_entry_add: @64 index=40e value=0
kvm_msr_entry_add: @65 index=40f value=0
kvm_msr_entry_add: @66 index=410 value=ffffffffffffffff
kvm_msr_entry_add: @67 index=411 value=0
kvm_msr_entry_add: @68 index=412 value=0
kvm_msr_entry_add: @69 index=413 value=0
kvm_msr_entry_add: @70 index=414 value=ffffffffffffffff
kvm_msr_entry_add: @71 index=415 value=0
kvm_msr_entry_add: @72 index=416 value=0
kvm_msr_entry_add: @73 index=417 value=0
kvm_msr_entry_add: @74 index=418 value=ffffffffffffffff
kvm_msr_entry_add: @75 index=419 value=0
kvm_msr_entry_add: @76 index=41a value=0
kvm_msr_entry_add: @77 index=41b value=0
kvm_msr_entry_add: @78 index=41c value=ffffffffffffffff
kvm_msr_entry_add: @79 index=41d value=0
kvm_msr_entry_add: @80 index=41e value=0
kvm_msr_entry_add: @81 index=41f value=0
kvm_msr_entry_add: @82 index=420 value=ffffffffffffffff
kvm_msr_entry_add: @83 index=421 value=0
kvm_msr_entry_add: @84 index=422 value=0
kvm_msr_entry_add: @85 index=423 value=0
kvm_msr_entry_add: @86 index=424 value=ffffffffffffffff
kvm_msr_entry_add: @87 index=425 value=0
kvm_msr_entry_add: @88 index=426 value=0
kvm_msr_entry_add: @89 index=427 value=0
kvm_put_msrs: ret=9 expected=90
qemu-custom: /root/qemu/target/i386/kvm.c:1849: kvm_put_msrs: Assertion `ret == 
cpu->kvm_msr_buf->nmsrs' failed.
Aborted

> Also, does the problem go away if you remove the +x2apic on the top
level qemu?

Don't think so, I actually added it because I thought it would solve
something. I can re-try with out it if needed(with the debug messages).

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https://bugs.launchpad.net/bugs/1665389

Title:
  Nested kvm guest fails to start on a emulated Westmere CPU guest under
  a Broadwell CPU host

Status in QEMU:
  New

Bug description:
  Using latest master(5dae13), qemu fails to start any nested guest in a
  Westmere emulated guest(layer 1), under a Broadwell host(layer 0),
  with the error:

  qemu-custom: /root/qemu/target/i386/kvm.c:1849: kvm_put_msrs:
  Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.

  The qemu command used(though other CPUs didn't work either):
  /usr/bin/qemu-custom -name guest=12ed9230-vm-el73,debug-threads=on -S -object 
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-5-12ed9230-vm-el73/master-key.aes
 -machine pc-i440fx-2.9,accel=kvm,usb=off -cpu Westmere,+vmx -m 512 -realtime 
mlock=off -smp 2,sockets=2,cores=1,threads=1 -object iothread,id=iothread1 
-uuid f4ce4eba-985f-42a3-94c4-6e4a8a530347 -nographic -no-user-config 
-nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-5-12ed9230-vm-el73/monitor.sock,server,nowait
 -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown 
-boot menu=off,strict=on -device 
virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x3 -drive 
file=/root/lago/.lago/default/images/vm-el73_root.qcow2,format=qcow2,if=none,id=drive-virtio-disk0,serial=1,discard=unmap
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
 -netdev tap,fd=26,id=hostnet0,vhost=on,vhostfd=28 -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=54:52:c0:a7:c8:02,bus=pci.0,addr=0x2 
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 
-chardev 
socket,id=charchannel0,path=/var/lib/libvirt/qemu/channel/target/domain-5-12ed9230-vm-el73/org.qemu.guest_agent.0,server,nowait
 -device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
 -object rng-random,id=objrng0,filename=/dev/random -device 
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9 -msg timestamp=on
  2017-02-16T15:14:45.840412Z qemu-custom: -chardev pty,id=charserial0: char 
device redirected to /dev/pts/2 (label charserial0)
  qemu-custom: /root/qemu/target/i386/kvm.c:1849: kvm_put_msrs: Assertion `ret 
== cpu->kvm_msr_buf->nmsrs' failed.

  
  The CPU flags in the Westmere guest:
  flags         : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat pse36 clflush mmx fxsr sse sse2 syscall nx lm constant_tsc rep_good nopl 
pni pclmulqdq vmx ssse3 cx16 sse4_1 sse4_2 x2apic popcnt aes hypervisor lahf_lm 
arat tpr_shadow vnmi flexpriority ept vpid

  The guest kernel is 3.10.0-514.2.2.el7.x86_64.

  The CPU flags of the host(Broadwell): 
  flags         : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov 
pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb 
rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology 
nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est 
tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt 
tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb 
intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle 
avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt xsaveopt xsavec 
xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp

  qemu command on the host - Broadwell(which works):
  /usr/bin/qemu-kvm -name 4ffcd448-vm-el73,debug-threads=on -S -machine 
pc-i440fx-2.6,accel=kvm,usb=off -cpu Westmere,+x2apic,+vmx,+vme -m 4096 
-realtime mlock=off -smp 2,sockets=2,cores=1,threads=1 -object 
iothread,id=iothread1 -uuid 8cc0a2cf-d25a-4014-acdb-f159c376a532 -nographic 
-no-user-config -nodefaults -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-4-4ffcd448-vm-el73/monitor.sock,server,nowait
 -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown 
-boot menu=off,strict=on -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x3 
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x4 -drive 
file=/home/ngoldin/src/nvgoldin.github.com/lago-init-files/.lago/flags-tests/default/images/vm-el73_root.qcow2,format=qcow2,if=none,id=drive-virtio-disk0,serial=1,discard=unmap
 -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
 -drive 
file=/home/ngoldin/src/nvgoldin.github.com/lago-init-files/.lago/flags-tests/default/images/vm-el73_additonal.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0,serial=2,discard=unmap
 -device 
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=2
 -netdev tap,fd=29,id=hostnet0,vhost=on,vhostfd=31 -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=54:52:c0:a8:c9:02,bus=pci.0,addr=0x2 
-chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 
-chardev 
socket,id=charchannel0,path=/var/lib/libvirt/qemu/channel/target/domain-4-4ffcd448-vm-el73/org.qemu.guest_agent.0,server,nowait
 -device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
 -object rng-random,id=objrng0,filename=/dev/random -device 
virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9 -msg timestamp=on

  On the Broadwell host I'm using a distribution package if it matters
  (qemu-kvm-2.6.2-5.fc24.x86_64 and 4.8.15-200.fc24.x86_64)

  As the error indicates, I think this assertion was put in:
  commit 48e1a45c3166d659f781171a47dabf4a187ed7a5
  Author: Paolo Bonzini <address@hidden>
  Date:   Wed Mar 30 22:55:29 2016 +0200

      target-i386: assert that KVM_GET/SET_MSRS can set all requested MSRs
      
      This would have caught the bug in the previous patch.
      
      Signed-off-by: Paolo Bonzini <address@hidden>

  I tried going back one commit before to 273c515, and then the error is gone 
and the nested guest comes up as expected. If I try to run with head at the 
above commit(48e145c) the error output is slightly different, though it looks 
the same:
  /root/qemu/target-i386/kvm.c:1713: kvm_put_msrs: Assertion `ret == n' failed.

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