Re: [PATCH 4/6] export new cpuid KVM_CAP

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On 04/27/2010 10:09 PM, Glauber Costa wrote:

Hmm.  We already have an API to get cpuid bits:
KVM_GET_SUPPORTED_CPUID2.  The nice thing about it is that it will
mean -cpu host will work out of the box.
Ok, from what I understand, KVM_GET_CPUID2 gets a set of features, and tells
userspace which of them are available. Right?

No. KVM_GET_CPUID2 reads what was set by KVM_SET_CPUID, as modified by the guest executing the cpuid instruction. KVM_GET_SUPPORTED_CPUID tells userspace which bits are supported by the host cpu and kvm.

If this is the case, userspace could ask for 0xffffffff, and then we tell them
which of them are present.

Does that make sense?

The API for KVM_GET_SUPPORTED_CPUID returns all cpuid leaves supported in one go, IIRC.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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