Re: [PATCH] fixup 3dnow! support

Avi Kivity
2008-05-07T08:13:01Z

Glauber Costa wrote:
> qemu recently added support for 3dnow instructions. Because of
> that, 3dnow will be featured among cpuid bits. But this will
> break kvm in cpus that don't have those instructions (which includes
> my laptop). So we fixup our cpuid before exposing it to the guest.
>
>

I've already fixed this in userspace.

In general I don't like silently modifying cpuid options in the kernel,
since that means we cannot be confident as to what the cpuid the guest
sees actually is, and so we can't be sure that migration will succeed.
Instead, the preferred path is to query what cpuid bits the host
support, pass that to the management app in order to compute the
greatest common subset, and tell the kernel to use that set.

nx is handled differently due to compatibility issues. In time we can
remove the special handling.

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