On 01/12/2011 11:54 AM, Nadav Har'El wrote:
On Wed, Jan 12, 2011, Xiao Guangrong wrote about "[PATCH v3 2/3] KVM: send IPI to vcpu only when it's in guest mode": > We can interrupt the vcpu only when it's running in guest mode > to reduce IPIHi, I am afraid there's a risk of confusion between the new vcpu->mode = IN_GUEST_MODE; and the existing is_guest_mode() (i.e., vcpu->arch.hflags& HF_GUEST_MASK) The latter says that the virtual cpu is in guest mode (i.e., the guest used VMLAUNCH and is runnning a nested guest), while the former says that the physical CPU that this vcpu is currently being run on, is in guest mode - or in other words, this vcpu is currently running. I'm not sure what is the best way to resolve this potential for confusion. Maybe on of them is better renamed (e.g., instead of vcpu->mode = IN_GUEST_MODE have something like vcpu->running = NOW_RUNNING). Or maybe some good comments need to to be written to explain the situation. Actually, I just noticed that there's already a vcpu->guest_mode which you are apparently replacing, so the potential for confusion is already in the current code... I.e., in the current code, is_guest_mode(vcpu) does NOT check vcpu->guest_mode...
Right. One is from the host's point of view, the other is from the guest's point of view. I'll rename is_guest_mode() to is_nested_guest().
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