Re: [kvm-devel] Re: expose host CPU features to guests

Avi Kivity
2007-09-09T13:14:44Z

Jamie Lokier wrote:
> Avi Kivity wrote:
>
>> Let's start with '-cpu host' as 'cpu host-cpuid' and implement '-cpu
>> host-os' on the first bug report? I have a feeling we won't ever see it.
>>
>
> I have a feeling you won't ever see it either, but not because it's a
> missing feature.
>
> Instead, I think a very small number of users will spend hours
> frustrated that some obscure guest doesn't work properly on their
> obscure x86 hardware, then they will learn that they should not use
> "-cpuid host" for that guest on that hardware, even though it works
> fine with other guests, and then their problem will be solved (albeit
> at a cost), and seen as such an obscure combination that it might
> never be reported to Qemu developers.
>
> In other words, host-os is what _I'd_ implement because I care too
> much about the poor obscure users and think it's the safe option, but
> I'm not doing the implementing here ;-)
>
> If you are curious what the differences are, do this in a current
> Linux source tree:
>
> egrep -R '(set|clear)_bit\(X86_FEATURE' arch/{i386,x86_64}/kernel
>
>

Some of these are Linux issues, not host cpu issues (for example, it
looks like VMI disables global pages).

Some of these issues may not impact the guest and we'd be removing them
unnecessarily. Also, kvm doesn't run on obscure hardware (although
kqemu does; qemu itself is not a candidate for -cpu host).

--
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