>The possibilities left are that either your Windows guest is lacking software updates that could perhaps improve its performance, or that 2D graphics really is that awful in combination with spectre/meltdown fixes.
Thanks Daniel. There are two problems with this explanation: 1. A native "bare metal" Windows 10 (1803) installation with all updates applied does NOT have any 2D performance problems. See my attachment (benchmarks) in the original post. 2. Both the Windows VM and the Linux VM do not see the microcode (version?), and therefore do not know about the Spectre vulnerability mitigation in the host kernel. However, the Microsoft document https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/CVE-2017-5715-and-hyper-v-vms suggests that Microsoft Hyper-V can be configured to expose new processor capabilities to guest virtual machines, specifically the ones made available through the microcode updates. Here a quote from the above Microsoft website: "Firmware updates from your OEM may contain new processor capabilities that can be used to protect against CVE-2017-5715 (IBRS, STIBP, IBPB). Once the virtualization host's firmware has been updated, the hypervisor can make these additional capabilities available to guest virtual machines after taking the following steps." The ideal behavior of qemu/kvm would be to expose the microcode capabilities to the guest (I suppose this happens partially as seen by the presence of the "pti ssbd ibrs ibpb" flags), but obviously something is missing. But the real important question is this: In the above scenario, are the VMs protected from Spectre vulnerabilities, simply by having the microcode installed in the host? Even when I disable the Spectre protection inside the Windows VM? -- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. 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 To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1788665/+subscriptions