[Solved]FYI//Re: [Qemu-devel] [Question] why x2apic's set by default without host support(on Nehalem CPU).

"Peter Huang(Peng)" <peter.huangpeng@xxxxxxxxxx> · Wed, 24 Jul 2013 10:54:57 +0800

    FYI, just for information sharing.

    KVM emulated x2apic feature no matter host supports it or not.

    You can get the code from arch/x86/kvm/cpuid.c.

    kvm_dev_ioctl_get_supported_cpuid
      ()->do_cpuid_ent()

      /*
        we support x2apic emulation even if host does not support
                     * it since
        we emulate x2apic
        in software */
                    entry->ecx
        |= F(X2APIC);

    QEMU will get this feature through kvm_ioctl().

    On 2013-07-24 8:48, Peter Huang(Peng) wrote:

      Hi,Jiri

Thanks for replying.

So why VM identified different features from host is due to the hypervisor filtering.
I will dig into the hypervisor of how it filter features, and update status later.

Thanks again.

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