On 04/15/2010 09:37 PM, Glauber Costa wrote:
Since we're changing the msrs kvmclock uses, we have to communicate that to the guest, through cpuid. We can add a new KVM_CAP to the hypervisor, and then patch userspace to recognize it. And if we ever add a new cpuid bit in the future, we have to do that again, which create some complexity and delay in feature adoption. Instead, what I'm proposing in this patch is a new capability, called KVM_CAP_X86_CPUID_FEATURE_LIST, that returns the current feature list currently supported by the hypervisor. If we ever want to add or remove some feature, we only need to tweak into the HV, leaving userspace untouched.
Hm. We need to update userspace anyway, since we don't like turning features on unconditionally (it breaks live migration into an older kernel).
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