[Qemu-devel] [Bug 994378] Re: Nested-virt)L1 (kvm on kvm)guest panic with parameter “-cpu host” in qemu command line.

[chao zhou]

this patch fixed the bug:
commit 338b522ca43cfd32d11a370f4203bcd089c6c877
Author: Kan Liang <address@hidden>
Date:   Mon Jul 14 12:25:56 2014 -0700

    perf/x86/intel: Protect LBR and extra_regs against KVM lying

    With -cpu host, KVM reports LBR and extra_regs support, if the host has
    support.

    When the guest perf driver tries to access LBR or extra_regs MSR,
    it #GPs all MSR accesses,since KVM doesn't handle LBR and extra_regs 
support.
    So check the related MSRs access right once at initialization time to avoid
    the error access at runtime.

    For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y
    (for host kernel).
    And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
    Start the guest with -cpu host.
    Run perf record with --branch-any or --branch-filter in guest to trigger LBR
    Run perf stat offcore events (E.g. LLC-loads/LLC-load-misses ...) in guest 
to
    trigger offcore_rsp #GP

    Signed-off-by: Kan Liang <address@hidden>
    Signed-off-by: Peter Zijlstra <address@hidden>
    Cc: Andi Kleen <address@hidden>
    Cc: Arnaldo Carvalho de Melo <address@hidden>
    Cc: Linus Torvalds <address@hidden>
    Cc: Maria Dimakopoulou <address@hidden>
    Cc: Mark Davies <address@hidden>
    Cc: Paul Mackerras <address@hidden>
    Cc: Stephane Eranian <address@hidden>
    Cc: Yan, Zheng <address@hidden>
    Link: http://lkml.kernel.org/r/address@hidden
    Signed-off-by: Ingo Molnar <address@hidden>

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https://bugs.launchpad.net/bugs/994378

Title:
  Nested-virt)L1 (kvm on kvm)guest panic with parameter “-cpu host” in
  qemu command line.

Status in QEMU:
  New

Bug description:
  Environment:
  ------------
  Host OS (ia32/ia32e/IA64):ia32e
  Guest OS (ia32/ia32e/IA64):ia32e
  Guest OS Type (Linux/Windows):Linux
  kvm.git Commit:19853301ef3289bda2d5264c1093e74efddaeab9
  qemu-kvm Commit:69abebf20280152da8fa7c418a819ae51e862231
  Host Kernel Version:3.4.0-rc3
  Hardware:WSM-EP, Romley-EP

  
  Bug detailed description:
  --------------------------
  (KVM on KVM) L1 guest panic when starting the L1 guest with “-cpu host” 
parameter in qemu command line.

  Note:
  1. when creating guest with “-cpu qemu64,+vmx”, L1 guest and L2 guest can boot
  up. 
  2. This should be a qemu-kvm bug. using '-cpu host' parameter, the following 
is the result.
  Kvm        + qemu-kvm =result
  19853301 + 69abebf2  = bad
  19853301 + 44755ea3  = good
  3. when booting up the guest with  the good commit of 19853301 + 44755ea3, 
you can see some
  error info, but nested virt works fine. (L1 and L2 guest can boot up.)
  “error: feature "i64" not available in set
  error: bad option value [extfeature_edx = i64 xd syscall]” 

  some logs 
  address@hidden x86_64-softmmu]# ./qemu-system-x86_64 -m 2048 -net 
nic,model=rtl8139 -net tap,script=/etc/kvm/qemu-ifup -hda /root/nested-kvm.qcow 
-cpu host
  error: feature "i64" not available in set
  error: bad option value [extfeature_edx = i64 xd syscall]
  error: feature "i64" not available in set
  error: bad option value [extfeature_edx = i64 xd syscall]
  error: feature "i64" not available in set
  error: bad option value [extfeature_edx = i64 syscall xd]
  error: feature "i64" not available in set
  error: bad option value [extfeature_edx = i64 syscall xd]
  VNC server running on `::1:5900'


  Reproduce steps:
  ----------------
  1.start up a host with kvm (commit: 19853301)
  2.rmmod kvm_intel
  3.modprobe kvm_intel nested=1
  4.qemu-system-x86_64 -m 2048  -hda L1-kvm.img -cpu host


  Current result:
  ----------------
  L1 guest panic.

  Expected result:
  ----------------
  L1 guest and L2 guest boot up correctly.

  Basic root-causing log:
  ----------------------

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