Re: [PATCH] fixup 3dnow! support

Glauber Costa
2008-05-06T23:08:39Z

Alexander Graf wrote:
>
> On May 6, 2008, at 6:27 PM, 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 actually don't see where the problem is here. As far as I read the
> code, the CPUID feature function gets received from the host CPU and
> bitwise ANDed with a bunch of features that are known to work. What's
> wrong with that approach?
Probably is that besides that known to work features, there are also
features that qemu puts in unconditionally. Among them, 3DNOW.

> But I'm pretty sure Dao can tell us a lot more about this.
Sure, it would be welcome.