On Tue, 17 Jul 2007, H. Peter Anvin wrote:
>
> S.Çağlar Onur wrote:
> >
> > If i'm not wrong X86_CMPXCHG64 depends on CONFIG_X86_PAE which depends on
> > HIGHMEM64 and again if i'm not wrong this means distributions who wants to
> > provide KVM must enable CONFIG_X86_PAE and CONFIG_HIGHMEM64G from now on?
> >
>
> X86_PAE should depend on X86_CMPXCHG64, not the other way around.
Actually, I think the *real* solution would be:
- add a X86_HAS_CMPXCHG8B config option, and set it for the appropriate
CPU selection (P6 and up, or whatever the rule is)
- make KVM depend on it
- make KVM and HIGHMEM64 _select_ another config option, namely the
NEEDS_CMPXCHG8B
and then we make the cpufeatures code check the CMPXCHG bit only if the
NEEDS_CMPXCHG8B thing is set. That gives us the best of all worlds.
Because there is no point in checking whether the CPU supports it if the
kernel doesn't _need_ it. Especially since we know that some CPU's lie
about it due to old NT bugs.
Linus
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