From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44694) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dL6Rm-0007bK-B9 for qemu-devel@nongnu.org; Wed, 14 Jun 2017 07:26:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dL6Rl-0008MF-FR for qemu-devel@nongnu.org; Wed, 14 Jun 2017 07:26:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45940) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dL6Rl-0008M6-8r for qemu-devel@nongnu.org; Wed, 14 Jun 2017 07:26:49 -0400 References: <20170606181948.16238-1-rkagan@virtuozzo.com> <20170606181948.16238-6-rkagan@virtuozzo.com> <20170613185752.GZ5016@thinpad.lan.raisama.net> <20170614112506.GI2004@rkaganb.sw.ru> From: Paolo Bonzini Message-ID: <6bb8f5e3-b6bf-c62a-93f3-9fe338d43881@redhat.com> Date: Wed, 14 Jun 2017 13:26:44 +0200 MIME-Version: 1.0 In-Reply-To: <20170614112506.GI2004@rkaganb.sw.ru> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 05/23] hyperv: ensure VP index equal to QEMU cpu_index List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Roman Kagan , Eduardo Habkost , qemu-devel@nongnu.org, Evgeny Yakovlev , "Denis V . Lunev" , Igor Mammedov On 14/06/2017 13:25, Roman Kagan wrote: >> The problem with that is that it will break as soon as we create >> VCPUs in a different order. Unsolvable on hosts that don't allow >> HV_X64_MSR_VP_INDEX to be set, however. > Right, thanks for putting together a detailed explanation. > > This was a thinko back then, not to have HV_X64_MSR_VP_INDEX maintained > by QEMU. I'm going to post a patch to KVM fixing that. > > Meanwhile QEMU needs a way to maintain its notion of vp_index that is > 1) in sync with kernel's notion > 2) also with kernels that don't support setting the msr > 3) persistent across migrations > > cpu_index looked like a perfect candidate. > What you want is the APIC id, which _is_ cpu_index but may not be in the future. But the APIC id is also the KVM vcpu_id, so there's no need to have VP_INDEX maintained by QEMU. Paolo