From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH 4/4] KVM: x86: allow hotplug of VCPU with APIC ID over 0xff Date: Mon, 5 Dec 2016 15:37:37 +0100 Message-ID: References: <20161202194401.10038-1-rkrcmar@redhat.com> <20161202194401.10038-5-rkrcmar@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: Paolo Bonzini , Igor Mammedov To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <20161202194401.10038-5-rkrcmar@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Am 02.12.2016 um 20:44 schrieb Radim Krčmář: > LAPIC after reset is in xAPIC mode, which poses a problem for hotplug of > VCPUs with high APIC ID, because reset VCPU is waiting for INIT/SIPI, > but there is no way to uniquely address it using xAPIC. > > From many possible options, we chose the one that also works on real > hardware: accepting interrupts addressed to LAPIC's x2APIC ID even in > xAPIC mode. > > KVM intentionally differs from real hardware, because real hardware > (Knights Landing) does just "x2apic_id & 0xff" to decide whether to > accept the interrupt in xAPIC mode and it can deliver one interrupt to > more than one physical destination, e.g. 0x123 to 0x123 and 0x23. > > Add a capability to let userspace know that we do something now. Should we allow user space to turn it on/off for compatibility handling? Or do we just not care? (or how will this capability be used later on?) -- David