commit f8f559422b (KVM: MMU: fast invalidate all mmio sptes) causeshang

[Markus Trippelsdorf]

The following commit:
 commit f8f559422b6c6a05469dfde614b67789b6142cb5
 Author: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
 Date:   Fri Jun 7 16:51:26 2013 +0800

    KVM: MMU: fast invalidate all mmio sptes

causes my kvm qemu qcow2 images to hang when they switch from the boot
console to the desktop. For example:
 qemu-system-x86_64 -enable-kvm -net nic,vlan=0,model=virtio -net user -drive file=ubuntu,if=virtio,cache=unsafe -smp 2 -m 1024
boots normally at first, but then hangs as soon as Xorg gets started.`

Perf top shows:
 20.99%  [kernel]                                  [k] svm_vcpu_run
 17.24%  [kernel]                                  [k] handle_mmio_page_fault_common
 15.61%  [kernel]                                  [k] kvm_arch_vcpu_ioctl_run
 12.49%  [kernel]                                  [k] fast_page_fault.part.78

I'm running:
QEMU emulator version 1.4.2 
on an AMD PhenomII X4 CPU.

-- 
Markus
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