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

[Jamie Lokier <jamie@shareable.org>]

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

-- Jamie