From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752247AbcIOQUb (ORCPT ); Thu, 15 Sep 2016 12:20:31 -0400 Received: from mail-db5eur01on0049.outbound.protection.outlook.com ([104.47.2.49]:27901 "EHLO EUR01-DB5-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751352AbcIOQUT (ORCPT ); Thu, 15 Sep 2016 12:20:19 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=mika.penttila@nextfour.com; Subject: Re: [PATCH] KVM: VMX: Enable MSR-BASED TPR shadow even if w/o APICv To: Wanpeng Li References: <1473839936-3393-1-git-send-email-wanpeng.li@hotmail.com> CC: "linux-kernel@vger.kernel.org" , kvm , Wanpeng Li , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wincy Van , Yang Zhang From: =?UTF-8?Q?Mika_Penttil=c3=a4?= Message-ID: <2c892ef7-9548-3765-1818-23a4ae885c4e@nextfour.com> Date: Thu, 15 Sep 2016 07:46:05 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; 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Commit (8d14695f9542 >>> x86, apicv: add virtual x2apic support) disable virtual x2apic mode >>> completely if w/o APICv, and the author also told me that windows guest >>> can't enter into x2apic mode when he developed the APICv feature several >>> years ago. However, it is not truth currently, Interrupt Remapping and >>> vIOMMU is added to qemu and the developers from Intel test windows 8 can >>> work in x2apic mode w/ Interrupt Remapping enabled recently. >>> >>> This patch enables TPR shadow for virtual x2apic mode to boost >>> windows guest in x2apic mode even if w/o APICv. >>> >>> Can pass the kvm-unit-test. >>> >> >> While at it, is the vmx flexpriotity stuff still valid code? >> AFAICS it gets enabled iff TPR shadow is on. flexpriority >> is on when : >> >> (flexpriority_enabled && lapic_in_kernel && cpu_has_vmx_tpr_shadow && cpu_has_vmx_virtualize_apic_accesses) >> >> But apic accesses to TPR mmio are not then trapped and TPR changes not reported because >> the “use TPR shadow” VM-execution control is 1. > > Please note the patch is for MSR-BASED TPR shadow w/o APICv, TPR > shadow can work correctly in other configurations. > > Regards, > Wanpeng Li > Hi, Yes I see, this is slightly offtopic but while at flexpriority, how is it relevant in current kvm? In other words I see it as dead code, because it is enabled only when TPR shadow is enabled, and as such ineffective because TPR shadow disables the wmexits tpr reporting uses. Thanks, Mika