Re: [Question] why x2apic's set by default without host support(on Nehalem CPU).

["Peter Huang(Peng)" <peter.huangpeng@huawei.com>]

[-- Attachment #1: Type: text/plain, Size: 1382 bytes --]

I traced the qemu process, and find out that host cpuid doesn't support x2apic,
but VM interception seems enabled x2apic.

with function=1(bit 21 indicates x2apic)
host_cpuid:ecx=0x009ce3bd
guest_cpuid:ecx=0x00b82201

On 2013-07-22 19:24, Peter Huang(Peng) wrote:
> Hi, Everyone
>
> I have been encountered a problem recently.
> My box uses Nehalem E5520 CPU, and this model doesn't support x2apic feature.
> I created a VM on KVM, and uses cpu mode=pass-through, I can get the right cpu
> model from the VM, but I can also see that the CPU in the vm supports x2apic.
>
> This seems werid.
> From QEMU's CPU model definition, Nehalem also doesn't support x2apic.
>
> Can anyone explain it?
>
> Thanks to you all!
>
> Below is the cpuinfo from host and guest:
> host:
> fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush
>  dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc
> arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni dtes64
> monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm dca sse4_1 sse4_2
> popcnt lahf_lm dtherm tpr_shadow vnmi flexpriority ept vpid
>
> vm:
> fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush
> mmx fxsr sse sse2 ss ht syscall nx rdtscp lm constant_tsc arch_perfmon rep_good
>  nopl pni ssse3 cx16 sse4_1 sse4_2 *x2apic *popcnt hypervisor lahf_lm

[-- Attachment #2: Type: text/html, Size: 3862 bytes --]