[Qemu-devel] [Bug 1722074] Re: warning: host doesn't support requested feature: CPUID.01H:ECX.vmx

[" Christian Ehrhardt " <1722074@bugs.launchpad.net>]

Hi,
this is not a show stopper at all.
It is just a warning and it is fine.
It is a trade-off between the "ease to use nested virt" vs "this warning".
For example on an intel chip you'd get:
  qemu-system-x86_64: warning: host doesn't support requested feature: CPUID.80000001H:ECX.svm
And that as well is no issue.

Since this is Ubuntu downstream decision to prefer simplicity for nested
virt I marked upstream qemu task invalid. There you'd not see the
warning, but instead would have to jump a few extra whoops to get
nesting working.

And finally, this code really is like that for longer than I take a look at it, so it might be that today one could solve it differently. There could be much more magic code to make it work as comfortable on both platforms and avoid the warning, but honestly - it wasn't an issue for many years, and I think it still is none.
So for the Ubuntu portion, I'll set confirmed+low(est) prio until it is clear that this really breaks something it didn't in the past years.

** Changed in: qemu (Ubuntu)
       Status: Incomplete => Confirmed

** Changed in: qemu (Ubuntu)
   Importance: Undecided => Wishlist

** Changed in: qemu (Ubuntu)
   Importance: Wishlist => Low

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https://bugs.launchpad.net/bugs/1722074

Title:
  warning: host doesn't support requested feature: CPUID.01H:ECX.vmx

Status in QEMU:
  Invalid
Status in qemu package in Ubuntu:
  Confirmed

Bug description:
  
  I encountered the bug today (when using qemu to boot up images - which used to work on my Intel CPU box):

  warning: host doesn't support requested feature: CPUID.01H:ECX.vmx

  The bug is a show-stopper - I completely cannot load my kernel images
  at all.

  My Ubuntu have this version of QEMU installed:

  qemu-system-x86_64 --version

  QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.16),
  Copyright (c) 2003-2008 Fabrice Bellard

  And PC is a AMD Ryzen7 CPU built, and this is the first time I am
  using it to load QEMU images.   My host information:

  cat /proc/cpuinfo |more

  processor	: 0
  vendor_id	: AuthenticAMD
  cpu family	: 23
  model		: 1
  model name	: AMD Ryzen 7 1700X Eight-Core Processor
  stepping	: 1
  microcode	: 0x800110e
  cpu MHz		: 2200.000
  cache size	: 512 KB
  physical id	: 0
  siblings	: 16
  core id		: 0
  cpu cores	: 8
  apicid		: 0
  initial apicid	: 0
  fpu		: yes
  fpu_exception	: yes
  cpuid level	: 13
  wp		: yes
  flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
  pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp
   lm constant_tsc rep_good nopl nonstop_tsc extd_apicid aperfmperf pni pclmulqdq
  monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf
  _lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw s
  kinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_l2 mwaitx hw_pstate
  vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt
  xsavec xgetbv1 xsaves clzero irperf arat npt lbrv svm_lock nrip_save tsc_scale v
  mcb_clean flushbyasid decodeassists pausefilter pfthreshold avic overflow_recov
  succor smca
  bugs		: fxsave_leak sysret_ss_attrs null_seg
  bogomips	: 6787.24
  TLB size	: 2560 4K pages
  clflush size	: 64
  cache_alignment	: 64
  address sizes	: 48 bits physical, 48 bits virtual
  power management: ts ttp tm hwpstate eff_freq_ro [13] [14]

  processor	: 1
  vendor_id	: AuthenticAMD
  cpu family	: 23
  model		: 1
  model name	: AMD Ryzen 7 1700X Eight-Core Processor
  stepping	: 1
  microcode	: 0x800110e
  cpu MHz		: 2200.000
  cache size	: 512 KB

  From other places, it can be seen that this is an AMD CPU issue:

  https://www.virtualmin.com/node/52227

  not sure?

  The bug will also affect the host negatively:  it will completely go
  into a hung mode - the entire host becomes completely unsable.

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