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Date: Mon, 11 Jul 2016 18:33:49 +0800 From: Yang Zhang <yang.zhang.wz@...il.com> To: Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, linux-kernel@...r.kernel.org, kvm@...r.kernel.org Cc: "Lan, Tianyu" <tianyu.lan@...el.com>, Igor Mammedov <imammedo@...hat.com>, Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com> Subject: Re: [PATCH v2 11/13] KVM: x86: add KVM_CAP_X2APIC_API On 2016/7/11 17:17, Paolo Bonzini wrote: > > > On 11/07/2016 10:56, Yang Zhang wrote: >> On 2016/7/11 15:44, Paolo Bonzini wrote: >>> >>> >>> On 11/07/2016 08:06, Yang Zhang wrote: >>>>> Changes to MSI addresses follow the format used by interrupt remapping >>>>> unit. >>>>> The upper address word, that used to be 0, contains upper 24 bits of >>>>> the LAPIC >>>>> address in its upper 24 bits. Lower 8 bits are reserved as 0. >>>>> Using the upper address word is not backward-compatible either as we >>>>> didn't >>>>> check that userspace zeroed the word. Reserved bits are still not >>>>> explicitly >>>> >>>> Does this means we cannot migrate the VM from KVM_CAP_X2APIC_API enabled >>>> host to the disable host even VM doesn't have more than 255 VCPUs? >>> >>> Yes, but that's why KVM_CAP_X2APIC_API is enabled manually. The idea is >>> that QEMU will not use KVM_CAP_X2APIC_API except on the newest machine >>> type. >> >> Thanks for confirmation. And when the KVM_CAP_X2APIC_API will be enabled >> in Qemu? > > It could be 2.7 or 2.8. > >>> >>> If interrupt remapping is on, KVM_CAP_X2APIC_API is needed even with 8 >>> VCPUs, I think. Otherwise KVM will believe that 0xff is "broadcast" >>> rather than "cluster 0, CPUs 0-7". >> >> If interrupt remapping is using, what 0xff means is relying on which >> mode the destination CPU is in. I think there is no KVM_CAP_X2APIC_API >> needed since interrupt remapping table gives all the information. > > If you have EIM 0xff never means broadcast, but KVM sees a 0xff in the > interrupt route or KVM_SIGNAL_MSI argument and translates it into a > broadcast. I see your point. I thought there would be a new irq router(like KVM_IRQ_ROUTING_IR) to handle all interrupts after turn on IR and KVM_CAP_X2APIC_API would be dropped. So we will continue to use KVM_IRQ_ROUTING_IRQCHIP and KVM_IRQ_ROUTING_MSI for interrupt from IR, right? -- best regards yang
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