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Re: [Qemu-devel] cpuid problem in upstream qemu with kvm


From: john cooper
Subject: Re: [Qemu-devel] cpuid problem in upstream qemu with kvm
Date: Mon, 21 Dec 2009 17:51:13 -0500
User-agent: Thunderbird 2.0.0.9 (X11/20071115)

Dor Laor wrote:

Qemu will check the required cpuid of the cpu model on the host and refuse to load otherwise. When moving to this model, migration can be simplified too since there are fewer combination, and one can choose performance over migration flexibility and wise versa. Due to the above check, the destination qemu won't load if the host does not support its cpu model.

If you're referring to the check in my patch, that's
currently advisory only.

The existing cpu model encoding of CPUID tosses flags
in to the soup on speculation they may be available
on the host.  If not it assumes they will be quietly
disabled on their way to the guest along with whatever
flags were enabled via +<flag> on the command line.
This mixed treatment for model implied vs. user
specified flags could be partly an artifact of trying
to adapt the legacy qemu64 model to whatever host
silicon it finds itself upon.

-john


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