[Qemu-devel] [Bug 1811533] Re: Unstable Win10 guest with qemu 3.1 + huge pages + hv_stimer

[Damir]

Still broken with Qemu 4.1rc2 /w Kernel 5.2.

This is a huge problem, as it breaks performance, either in networking
(you can't use the virtio net which is the only 100G adapter afaik), or
you have to disable huge pages, which is a blow to any large vm host, or
it breaks stimer, which increases cpu usage, generally breaking
virtualization.

Thank you!

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https://bugs.launchpad.net/bugs/1811533

Title:
  Unstable Win10 guest with qemu 3.1 + huge pages + hv_stimer

Status in QEMU:
  New

Bug description:
  Host:
  Gentoo linux x86_64, kernel 4.20.1
  Qemu 3.1.0 
  CPU: Intel i7 6850K
  Chipset: X99

  Guest:
  Windows 10 Pro 64bit (1809)
  Machine type: pc-q35_3.1
  Hyper-V enlightenments: 
hv_stimer,hv_reenlightenment,hv_frequencies,hv_vapic,hv_reset,hv_synic,hv_runtime,hv_vpindex,hv_time,hv_relaxed,hv_spinlocks=0x1fff
  Memory: 16GB backed by 2MB huge pages

  Issue:
  Once guest is started, log gets flooded with:

  qemu-system-x86_64: vhost_region_add_section: Overlapping but not
  coherent sections at 103000

  or

  qemu-system-x86_64: vhost_region_add_section:Section rounded to 0
  prior to previous 1f000

  (line endings change)

  and as time goes guest loses network access (virtio-net-pci) and
  general performance diminishes to extent of freezing applications.

  Observations:
  1) problem disappears when hv_stimer is removed
  2) problem disappears when memory backing with huge pages is disabled
  3) problem disappears when machine type is downgraded to pc-q35_3.0

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