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Date: Tue, 22 Dec 2009 23:02:38 +0000
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Qemu-devel] cpuid problem in upstream qemu with kvm
Message-ID: <20091222230238.GD19806@shareable.org>
References: <4B2DF334.6030208@redhat.com> <20091220155101.GB31257@redhat.com>
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, Avi Kivity <avi@redhat.com>, Gleb Natapov <gleb@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

Anthony Liguori wrote:
> It would be insane to emulate sse3 too.

It doesn't sound too ridiculous if TCG is involved, provided the
switching between TCG and KVM isn't too rapid.  TCG is slower, but
it's not ridiculously slow.

Though, I don't expect anyone to volunteer to implement it :-)

> how likely is it that any given guest is using an obscure feature?

Could KVM detect when a guest starts using each feature?  For example,
by disabling access to those features, enabling each one when the KVM
trap occurs and recording that fact?  Is it possible to enable them in
the guest-visible cpuid, but force a trap on access to them?

That might be quite useful information when you want to migrate
something that wasn't planned for X years ago.

-- Jamie