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[Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows
From: |
Daniel Berrange |
Subject: |
[Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection |
Date: |
Thu, 30 Aug 2018 16:11:13 -0000 |
There is always a performance differential between bare metal & VMs. The
actual amount varies depending on alot of different factors and
meltdown/spectre have had an effect here - the actual perf hit depends
on the CPU models & virtual hardware and more besides - ranging anywhere
from 0% to 40% perf hit
The guest VM *does* know about the Spectre mitigation because it is
being given the "ibrs" feature which is sufficient for guest OS to
mitigate the problem. STIBP is only needed by the host. Exposing
microcode version to the guest is not required as OS should only need to
look at the features provided to determine if it can mitigate the flaws.
The complaints about microcode version from spectre-meltdown-checker.sh
are a bug in that script. The important parts are the "STATUS: NOT
VULNERABLE" lines
If you disable Spectre protection in the Windows VM, then it is not
protected from Spectre. The hypervisor protects itself, and exposes the
CPU feature(s) that enable the guest to activate its own protection. The
hypervisor won't protect the guest directly - it just gives it the tools
needed to protect itself.
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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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- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, (continued)
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Daniel Berrange, 2018/08/24
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/24
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/25
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/25
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Daniel Berrange, 2018/08/28
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/28
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/30
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/30
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Daniel Berrange, 2018/08/30
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/30
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection,
Daniel Berrange <=
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Heiko Sieger, 2018/08/30
- [Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows 10 (1803) VGA passthrough VM using "Spectre" protection, Dr. David Alan Gilbert, 2018/08/31