Comment 19 for bug 1788665

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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