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[Qemu-devel] [Bug 1788665] Re: Low 2D graphics performance with Windows

From: Heiko Sieger
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 11:08:41 -0000

Downloaded and ran the spectre-meltdown-checker.sh

$ spectre-meltdown-checker.sh 
Spectre and Meltdown mitigation detection tool v0.39+

Checking for vulnerabilities on current system
Kernel is Linux 4.15.0-33-generic #36-Ubuntu SMP Wed Aug 15 16:00:05 UTC 2018 
CPU is Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz

Hardware check
* Hardware support (CPU microcode) for mitigation techniques
  * Indirect Branch Restricted Speculation (IBRS)
    * SPEC_CTRL MSR is available:  YES 
    * CPU indicates IBRS capability:  YES  (SPEC_CTRL feature bit)
  * Indirect Branch Prediction Barrier (IBPB)
    * PRED_CMD MSR is available:  YES 
    * CPU indicates IBPB capability:  YES  (SPEC_CTRL feature bit)
  * Single Thread Indirect Branch Predictors (STIBP)
    * SPEC_CTRL MSR is available:  YES 
    * CPU indicates STIBP capability:  NO 
  * Speculative Store Bypass Disable (SSBD)
    * CPU indicates SSBD capability:  YES  (Intel SSBD)
  * L1 data cache invalidation
    * FLUSH_CMD MSR is available:  YES 
  * Enhanced IBRS (IBRS_ALL)
    * CPU indicates ARCH_CAPABILITIES MSR availability:  NO 
    * ARCH_CAPABILITIES MSR advertises IBRS_ALL capability:  NO 
  * CPU explicitly indicates not being vulnerable to Meltdown (RDCL_NO):  NO 
  * CPU explicitly indicates not being vulnerable to Variant 4 (SSB_NO):  NO 
  * Hypervisor indicates host CPU might be vulnerable to RSB underflow (RSBA):  
  * CPU microcode is known to cause stability problems:  NO  (model 0x2d family 
0x6 stepping 0x7 ucode 0x1 cpuid 0x206d7)
  * CPU microcode is the latest known available version:  NO  (latest known 
version is 0x714 according to Intel Microcode Guidance, August 8 2018)
* CPU vulnerability to the speculative execution attack variants
  * Vulnerable to Variant 1:  YES 
  * Vulnerable to Variant 2:  YES 
  * Vulnerable to Variant 3:  YES 
  * Vulnerable to Variant 3a:  YES 
  * Vulnerable to Variant 4:  YES 
  * Vulnerable to Variant l1tf:  YES 

CVE-2017-5753 [bounds check bypass] aka 'Spectre Variant 1'
* Mitigated according to the /sys interface:  YES  (Mitigation: __user pointer 
* Kernel has array_index_mask_nospec:  YES  (1 occurrence(s) found of x86 64 
bits array_index_mask_nospec())
* Kernel has the Red Hat/Ubuntu patch:  NO 
* Kernel has mask_nospec64 (arm64):  NO 
> STATUS:  NOT VULNERABLE  (Mitigation: __user pointer sanitization)

CVE-2017-5715 [branch target injection] aka 'Spectre Variant 2'
* Mitigated according to the /sys interface:  YES  (Mitigation: Full generic 
retpoline, IBPB, IBRS_FW)
* Mitigation 1
  * Kernel is compiled with IBRS support:  YES 
    * IBRS enabled and active:  YES  (for kernel and firmware code)
  * Kernel is compiled with IBPB support:  YES 
    * IBPB enabled and active:  YES 
* Mitigation 2
  * Kernel has branch predictor hardening (arm):  NO 
  * Kernel compiled with retpoline option:  YES 
    * Kernel compiled with a retpoline-aware compiler:  YES  (kernel reports 
full retpoline compilation)
> STATUS:  NOT VULNERABLE  (Full retpoline + IBPB are mitigating the 
> vulnerability)

CVE-2017-5754 [rogue data cache load] aka 'Meltdown' aka 'Variant 3'
* Mitigated according to the /sys interface:  YES  (Mitigation: PTI)
* Kernel supports Page Table Isolation (PTI):  YES 
  * PTI enabled and active:  YES 
  * Reduced performance impact of PTI:  YES  (CPU supports PCID, performance 
impact of PTI will be reduced)
* Running as a Xen PV DomU:  NO 

CVE-2018-3640 [rogue system register read] aka 'Variant 3a'
* CPU microcode mitigates the vulnerability:  YES 
> STATUS:  NOT VULNERABLE  (your CPU microcode mitigates the vulnerability)

CVE-2018-3639 [speculative store bypass] aka 'Variant 4'
* Mitigated according to the /sys interface:  YES  (Mitigation: Speculative 
Store Bypass disabled via prctl and seccomp)
* Kernel supports speculation store bypass:  YES  (found in /proc/self/status)
> STATUS:  NOT VULNERABLE  (Mitigation: Speculative Store Bypass disabled via 
> prctl and seccomp)

CVE-2018-3615/3620/3646 [L1 terminal fault] aka 'Foreshadow & Foreshadow-NG'
* Mitigated according to the /sys interface:  YES  (Mitigation: PTE Inversion; 
VMX: conditional cache flushes, SMT vulnerable)
> STATUS:  NOT VULNERABLE  (Mitigation: PTE Inversion; VMX: conditional cache 
> flushes, SMT vulnerable)

It shows that the microcode is not updated, and reports vulnerability.

If I understand correctly, the Linux VM should not install the
microcode, but report the microcode features of the host.

     * CPU indicates STIBP capability:  NO

Obviously stibp is not passed to the guest.

Is there any other/better way to pass the host cpu capabilities to the

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2017-5753

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2017-5754

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-3615

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-3639

** CVE added: https://cve.mitre.org/cgi-bin/cvename.cgi?name=2018-3640

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

Status in QEMU:

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

  Expected behavior:
  qemu/kvm hypervisor to expose firmware capabilities of host to guest OS - see 


  Starting in March or April Microsoft began to push driver updates in
  their updates / security updates. See https://support.microsoft.com

  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

  A bare metal Windows installation does not display a performance loss
  after the update. See https://heiko-sieger.info/low-2d-graphics-

  Similar reports can be found here:


  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 = 
  [    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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