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

From: "Peter Huang(Peng)" <peter.huangpeng@huawei.com>
To: Eduardo Habkost <ehabkost@redhat.com>,
	libvir-list@redhat.com, qemu-devel@nongnu.org,
	Jiri Denemark <jdenemar@redhat.com>
Subject: [Qemu-devel] [Solved]FYI//Re: [Question] why x2apic's set by default without host support(on Nehalem CPU).
Date: Wed, 24 Jul 2013 10:54:57 +0800	[thread overview]
Message-ID: <51EF4201.9040802@huawei.com> (raw)
In-Reply-To: <51EF2469.1090402@huawei.com>

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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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