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Re: [Qemu-devel] [qemu-devel] Bug Report: VM crashed for some kinds of v
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From: |
Jan Kiszka |
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Subject: |
Re: [Qemu-devel] [qemu-devel] Bug Report: VM crashed for some kinds of vCPU in nested virtualization |
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Date: |
Tue, 16 Apr 2013 12:29:12 +0200 |
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User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
On 2013-04-16 12:19, 李春奇 <Arthur Chunqi Li> wrote:
> I looked up Intel manual for VM instruction error. Error number 7 means "VM
> entry with invalid control field(s)", which means in process of VM
> switching some control fields are not properly configured.
>
> I wonder why some emulated CPUs (e.g.Nehalem) can run properly without
> nested VMCS MSR support?
MSRs are only switched between host (L0) and guest (L1/L2) if their
value differ. That saves some cycles. Therefore, if either the guest is
not using a specific MSR (due to differences in the virtual CPU feature
set) or it is using it in the same way like the host, there is no
switching, thus no risk to hit this unimplemented feature.
Jan
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