On 09/23/2009 10:37 PM, Avi Kivity wrote:
Example: feature negotiation. If it happens in userspace, it's easy to limit what features we expose to the guest. If it happens in the kernel, we need to add an interface to let the kernel know which features it should expose to the guest. We also need to add an interface to let userspace know which features were negotiated, if we want to implement live migration. Something fairly trivial bloats rapidly.
btw, we have this issue with kvm reporting cpuid bits to the guest. Instead of letting kvm talk directly to the hardware and the guest, kvm gets the cpuid bits from the hardware, strips away features it doesn't support, exposes that to userspace, and expects userspace to program the cpuid bits it wants to expose to the guest (which may be different than what kvm exposed to userspace, and different from guest to guest).
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