[Qemu-devel] [Bug 1788665] [NEW] Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection

[Heiko Sieger]

Public bug reported:

Windows 10 (1803) VM using VGA passthrough via qemu script.

After upgrading Windows 10 Pro VM to version 1803, or possibly after
applying the March/April security updates from Microsoft, the VM would
show low 2D graphics performance (sluggishness in 2D applications and
low Passmark results).

Turning off Spectre vulnerability protection in Windows remedies the
issue.

Expected behavior:
qemu/kvm hypervisor to expose firmware capabilities of host to guest OS - see 
https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/CVE-2017-5715-and-hyper-v-vms

Background:

Starting in March or April Microsoft began to push driver updates in
their updates / security updates. See https://support.microsoft.com/en-
us/help/4073757/protect-your-windows-devices-against-spectre-meltdown

One update concerns the Intel microcode - see
https://support.microsoft.com/en-us/help/4100347. It is activated by
default within Windows.

Once the updates are applied within the Windows guest, 2D graphics
performance drops significantly. Other performance benchmarks are not
affected.

A bare metal Windows installation does not display a performance loss
after the update. See https://heiko-sieger.info/low-2d-graphics-
benchmark-with-windows-10-1803-kvm-vm/

Similar reports can be found here:
https://www.reddit.com/r/VFIO/comments/97unx4/passmark_lousy_2d_graphics_performance_on_windows/

Hardware:

6 core Intel Core i7-3930K (-MT-MCP-)

Host OS:
Linux Mint 19/Ubuntu 18.04
Kernel: 4.15.0-32-generic x86_64
Qemu: QEMU emulator version 2.11.1
Intel microcode (host): 0x714
dmesg | grep microcode
[    0.000000] microcode: microcode updated early to revision 0x714, date = 
2018-05-08
[    2.810683] microcode: sig=0x206d7, pf=0x4, revision=0x714
[    2.813340] microcode: Microcode Update Driver: v2.2.

Note: I manually updated the Intel microcode on the host from 0x713 to
0x714. However, both microcode versions produce the same result in the
Windows guest.

Guest OS:
Windows 10 Pro 64 bit, release 1803

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: intel microcode spectre

** Attachment added: "Red graph - Windows 10 bare metal; blue graph - Windows 
10 VM with Spectre protection enabled; yellow graph - Windows 10 VM with 
spectre protection disabled"
   
https://bugs.launchpad.net/bugs/1788665/+attachment/5179857/+files/Capture-20180817-4-spectre-disabled-0x714-2d.PNG

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https://bugs.launchpad.net/bugs/1788665

Title:
  Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM
  using "Spectre" protection

Status in QEMU:
  New

Bug description:
  Windows 10 (1803) VM using VGA passthrough via qemu script.

  After upgrading Windows 10 Pro VM to version 1803, or possibly after
  applying the March/April security updates from Microsoft, the VM would
  show low 2D graphics performance (sluggishness in 2D applications and
  low Passmark results).

  Turning off Spectre vulnerability protection in Windows remedies the
  issue.

  Expected behavior:
  qemu/kvm hypervisor to expose firmware capabilities of host to guest OS - see 
https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/CVE-2017-5715-and-hyper-v-vms

  Background:

  Starting in March or April Microsoft began to push driver updates in
  their updates / security updates. See https://support.microsoft.com
  /en-us/help/4073757/protect-your-windows-devices-against-spectre-
  meltdown

  One update concerns the Intel microcode - see
  https://support.microsoft.com/en-us/help/4100347. It is activated by
  default within Windows.

  Once the updates are applied within the Windows guest, 2D graphics
  performance drops significantly. Other performance benchmarks are not
  affected.

  A bare metal Windows installation does not display a performance loss
  after the update. See https://heiko-sieger.info/low-2d-graphics-
  benchmark-with-windows-10-1803-kvm-vm/

  Similar reports can be found here:
  
https://www.reddit.com/r/VFIO/comments/97unx4/passmark_lousy_2d_graphics_performance_on_windows/

  Hardware:

  6 core Intel Core i7-3930K (-MT-MCP-)

  Host OS:
  Linux Mint 19/Ubuntu 18.04
  Kernel: 4.15.0-32-generic x86_64
  Qemu: QEMU emulator version 2.11.1
  Intel microcode (host): 0x714
  dmesg | grep microcode
  [    0.000000] microcode: microcode updated early to revision 0x714, date = 
2018-05-08
  [    2.810683] microcode: sig=0x206d7, pf=0x4, revision=0x714
  [    2.813340] microcode: Microcode Update Driver: v2.2.

  Note: I manually updated the Intel microcode on the host from 0x713 to
  0x714. However, both microcode versions produce the same result in the
  Windows guest.

  Guest OS:
  Windows 10 Pro 64 bit, release 1803

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