On Mon, Apr 30, 2012 at 11:22:34AM +0300, Avi Kivity wrote: > On 04/29/2012 04:52 PM, Gleb Natapov wrote: > > On Sun, Apr 29, 2012 at 04:26:21PM +0300, Avi Kivity wrote: > > > On 04/29/2012 04:20 PM, Gleb Natapov wrote: > > > > > > This is too similar to kvm_irq_delivery_to_apic(). Why not reuse it. We > > > > > > can use one of reserved delivery modes as PV delivery mode. We will > > > > > > disallow guest to trigger it through apic interface, so this will not be > > > > > > part of ABI and can be changed at will. > > > > > > > > > > > > > > > > I'm not thrilled about this. Those delivery modes will eventually > > > > > become unreserved. We can have a kvm_lookup_apic_id() that is shared > > > > > among implementations. > > > > > > > > > This is only internal implementation. If they become unreserved we will > > > > use something else. > > > > > > > > > > Yeah, I'm thinking of that time. Why do something temporary and fragile? > > > > > Why is it fragile? Just by unreserving the value Intel will not break > > KVM. Only when KVM will implement apic feature that unreserves the value > > we will have to change internal implementation and use another value, > > but this will be done by the same patch that does unreserving. The > > unreserving may even never happen. > > Some remains of that may leak somewhere. I do not see where. APIC code should #GP if a guest attempts to set reserved values through APIC interface, or at least ignore them. > Why not add an extra > parameter? Yes, we can add extra parameter to "struct kvm_lapic_irq" and propagate it to __apic_accept_irq(). We can do that now, or when Intel unreserve all reserved values. I prefer the later since I do not believe it will happen in observable feature. > Or do something like > > kvm_for_each_apic_dest(vcpu, apic_destination) { > ... > } > > That can be reused in both the apic code and pv kick. > That's exactly what kvm_irq_delivery_to_apic() is. > > Meanwhile kvm_irq_delivery_to_apic() > > will likely be optimized to use hash for unicast delivery and unhalt > > hypercall will benefit from it immediately. > > Overloading delivery mode is not the only way to achieve sharing. > It is simplest and most straightforward with no demonstratable drawbacks :) Adding parameter to "struct kvm_lapic_irq" is next best thing. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html