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[Xen-devel] RE: expose MWAIT to dom0
>>> On 15.08.11 at 09:57, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
> So how about the change like below?
> - __clear_bit(X86_FEATURE_MWAIT % 32, &c);
> + if ( !IS_PRIV(current->domain) || !xen_cpuidle )
> + __clear_bit(X86_FEATURE_MWAIT % 32, &c);
You'd break any Dom0 kernel that uses the flag to determine whether it
can actually use the mwait/monitor instructions. I agree with Keir that
for this particular purpose the code ought to look at the real CPUID
It should be possible to do this without changing non-Xen code, since
the use of the instructions is additionally gated on CPUID leaf 5
producing non-zero output. But again, the kernel has to do this for
itself, the hypervisor shouldn't expose the feature flag.
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