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[libvirt] [question] doubt about cpu model 'qemu64'



Hello,
    Recently I noticed that if I gave no model to qemu, then I would get 'qemu64' as default cpu model. 
Model 'qemu64' defined in qemu and defined in libvirt both support feature 'svm'. And if I start a VM with 
'qemu64' as the qemu default model, I can get no 'svm' feature in the GuestOS:
    fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht pni cx16 popcnt hypervisor syscall nx lm lahf_lm

    My host cpu is intel E5620, and it doesn't support 'svm' feature:
    'fpu', 'vme', 'de', 'pse', 'tsc', 'msr', 'pae', 'mce', 'cx8', 'apic', 'sep', 'mtrr', 'pge', 'mca', 'cmov', 'pat', 'pse36', 
'clflush', 'ds', 'acpi', 'mmx', 'fxsr', 'sse', 'sse2', 'ss', 'ht', 'tm', 'pbe', 'pni', 'pclmulqdq', 'dtes64', 'monitor', 'ds_cpl', 
'vmx', 'smx', 'est', 'tm2', 'ssse3', 'cx16', 'xtpr', 'pdcm', 'pcid', 'dca', 'sse4.1', 'sse4.2', 'popcnt', 'aes', 'syscall', 'nx', 
'pdpe1gb', 'rdtscp', 'lm', 'lahf_lm', 'dts', 'arat', 'constant_tsc'

    I can get the same result with libvirt API compareCPU on the host:
    model:qemu64; ret:0
    model:Conroe; ret:2
    model:Penryn; ret:2
    model:Nehalem; ret:2
    model:Westmere; ret:2
    model:SandyBridge; ret:0
    model:Haswell; ret:0

    Isn't it strange that the host cpu doesn't support 'qemu64' model, but we can still start a VM with 'qemu64' as 
the default model on it?

Best Regards,
-WangYufei



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