2015-12-22 14:42+0800, Yang Zhang: > On 2015/12/22 12:36, Wu, Feng wrote: >>>From: Yang Zhang [mailto:yang.zhang.wz@xxxxxxxxx] >>>On 2015/12/21 9:55, Wu, Feng wrote: >>>>>From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel- >>>>>On 2015/12/16 9:37, Feng Wu wrote: >>>>>>diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>>>>@@ -10702,8 +10702,16 @@ static int vmx_update_pi_irte(struct kvm >>>*kvm, >>>>>unsigned int host_irq, >>>>>> */ >>>>>> >>>>>> kvm_set_msi_irq(e, &irq); >>>>>>- if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) >>>>>>- continue; >>>>>>+ >>>>>>+ if (!kvm_intr_is_single_vcpu(kvm, &irq, &vcpu)) { >>>>>>+ if (!kvm_vector_hashing_enabled() || >>>>>>+ irq.delivery_mode != >>>>>APIC_DM_LOWEST) >>>>>>+ continue; >>>>>>+ >>>>>>+ vcpu = kvm_intr_vector_hashing_dest(kvm, &irq); >>>>>>+ if (!vcpu) >>>>>>+ continue; >>>>>>+ } >>>>> >>>>>I am a little confused with the 'continue'. If the destination is not >>>>>single vcpu, shouldn't we rollback to use non-PI mode? >>>> >>>>Here is the logic: >>>>- If it is single destination, we will use PI no matter it is fixed or lowest-priority. >>>>- If it is not single destination: >>>> a) It is fixed, we will use non-PI >>>> b) It is lowest-priority and vector-hashing is enabled, we will use PI >>>> c) otherwise, use non-PI >>> >>>If it is single destination previously, then change to no-single mode. >>>Can current code cover this case? >> >>In my test, before setting irq affinity (change single vcpu to non-single vcpu >>in this case), the guest will mask the interrupt first, so before getting here, IRTE >>has been changed back to remapped mode already(when guest masks the MSIx, >>we will change back to remapped mode), hence nothing needed here. >> >>Digging into the linux code (guest) a bit more, I found that if interrupt remapping >>is not enabled in the guest (IR is not supported for guest anyway), it will always >>mask the MSI/MSIx before setting the irq affinity. So the code should work >>well currently. > > We should not rely on guest's behavior. From code level, it need be fixed. > >>However, for robustness, I think explicitly changing IRTE back to remapped >>mode for the 'continue' case should be a good idea. > > This is what i am looking for. I agree, that would be a nice addition. IIRC, the masking is optional -- if the guest can handle interrupts that are generated while the device is half-configured, it doesn't need to disable MSIs. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
