I won’t be able to run any tests for the next 16 days at the very least, as I’m traveling.



> On 5 Sep 2018, at 13:21, Dr. David Alan Gilbert <email address hidden> wrote:
> 
> I don't have the nvidia for pass through to try this with; but I suggest
> that you try the following:
> 
>  a) Start a windows vm running an older version unaffected by the bug and start a 2d test 
>  b) run 'perf top' on the host while the test is running and capture the results
>     - make sure you have debug symbols for both qemu (and related libraries) and the kernel 
>  c) now repeat a/b for the newer version of windows that's affected
> 
> add the results of the 'perf top' to this bug; hopefully we'll be able
> to see qemu or the kernel spending a lot more time in some particular
> routine in the new version.
> 
> -- 
> You received this bug notification because you are subscribed to the bug
> report.
> 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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