Re: i686 quirk for AMD Geode

Avi Kivity
2009-11-10T19:51:09Z

On 11/10/2009 08:49 PM, H. Peter Anvin wrote:
>
>> Why is using KVM doing it right ? It sounds like its doing it slowly,
>> and hideously memory inefficiently. You are solving an uninteresting
>> general case problem when you just need two tiny fixups (or perhaps 3 if
>> you want to fix up early x86-64 prefetch)
>>
> Why do we only need "two tiny fixups"? Where do we draw the line in
> terms of ISA compatibility? One could easily argue that the Right
> Thing[TM] is to be able to process any optional instruction -- otherwise
> one has a very difficult place to draw a line.
>
> Consider SSE3, for example. Why should the same concept not apply to
> SSE3 instructions as to CMOV?
>

Because then user programs would run 20x or more slower than the user
expects. Better to terminate early (and teach userspace how to choose
the instruction subset correctly).

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.