[Qemu-devel] [Bug 1661386] Re: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed

[Dr. David Alan Gilbert]

Hi Matwey,
  That shouldn't happen!  The patch you've bisected to is just the one that 
complains if the ioctl fails rather than silently ignoring the failure - it 
means the failure probably previously existed and was ignored and that causes 
random other problems.

What kernel are you using on the host?

We need to figure out which MSR it's objecting to; probably the easiest
way is to :

1) Edit mvm_msr_entry_add in target/i386/kvm.c to something like:

    assert((void *)(entry + 1) <= limit);
    fprintf(stderr,"kvm_msr_entry_add: @%d index=%x value=%lx\n", msrs->nmsrs, 
index, value);
    entry->index = index;

2) edit kvm_put_msrs near the bottom:

    fprintf(stderr,"kvm_put_msrs: ret=%d expected=%d\n", ret, 
cpu->kvm_msr_buf->nmsrs);
    assert(ret == cpu->kvm_msr_buf->nmsrs);

Now with any luck the 'ret' value will tell you the entry which is bad, and you 
can match
that to the @%d value (or maybe it's the entry before that one which failed?) 
then we get the index, look it up in the intel docs and figure out which MSR 
it's complaining about.

Dave

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https://bugs.launchpad.net/bugs/1661386

Title:
  Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed

Status in QEMU:
  New

Bug description:
  Hello,

  
  I see the following when try to run qemu from master as the following:

  # ./x86_64-softmmu/qemu-system-x86_64 --version
  QEMU emulator version 2.8.50 (v2.8.0-1006-g4e9f524)
  Copyright (c) 2003-2016 Fabrice Bellard and the QEMU Project developers
  # ./x86_64-softmmu/qemu-system-x86_64 -machine accel=kvm -nodefaults
  -no-reboot -nographic -cpu host -vga none  -kernel .build.kernel.kvm
  -initrd .build.initrd.kvm -append 'panic=1 no-kvmclock console=ttyS0
  loglevel=7' -m 1024 -serial stdio
  qemu-system-x86_64: /home/matwey/lab/qemu/target/i386/kvm.c:1849:
  kvm_put_msrs: Assertion `ret == cpu->kvm_msr_buf->nmsrs' failed.

  First broken commit has been bisected:

  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>

  My cpuinfo is the following:

  processor       : 0
  vendor_id       : GenuineIntel
  cpu family      : 6
  model           : 44
  model name      : Intel(R) Xeon(R) CPU           X5675  @ 3.07GHz
  stepping        : 2
  microcode       : 0x14
  cpu MHz         : 3066.775
  cache size      : 12288 KB
  physical id     : 0
  siblings        : 2
  core id         : 0
  cpu cores       : 2
  apicid          : 0
  initial apicid  : 0
  fpu             : yes
  fpu_exception   : yes
  cpuid level     : 11
  wp              : yes
  flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca 
cmov pat pse36 clflush dts mmx fxsr sse sse2 ss ht syscall nx rdtscp lm 
constant_tsc arch_perfmon pebs bts nopl xtopology tsc_reliable nonstop_tsc 
aperfmperf pni pclmulqdq vmx ssse3 cx16 sse4_1 sse4_2 popcnt aes hypervisor 
lahf_lm ida arat epb dtherm tpr_shadow vnmi ept vpid
  bugs            :
  bogomips        : 6133.55
  clflush size    : 64
  cache_alignment : 64
  address sizes   : 40 bits physical, 48 bits virtual
  power management:

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