From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753440AbaCJMXx (ORCPT ); Mon, 10 Mar 2014 08:23:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:28054 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752423AbaCJMXw (ORCPT ); Mon, 10 Mar 2014 08:23:52 -0400 Date: Mon, 10 Mar 2014 13:23:43 +0100 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, alex.williamson@redhat.com, mtosatti@redhat.com, gleb@kernel.org, jan.kiszka@siemens.com Subject: Re: [PATCH 0/7] KVM: x86: Let the guest write to multiple debug registers with one vmexit Message-ID: <20140310122342.GA16392@potion.brq.redhat.com> References: <1394192571-11056-1-git-send-email-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1394192571-11056-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-03-07 12:42+0100, Paolo Bonzini: > Alex Williamson reported that a Windows game does something weird that > makes the guest save and restore debug registers on each context switch. > This cause several hundred thousands vmexits per second, and basically > cuts performance in half when running under KVM. > > However, when not running in guest-debug mode, the guest controls the > debug registers and having to take an exit for each DR access is a waste > of time. We just need one vmexit to load any stale values of DR0-DR6, > and then we can let the guest run freely. On the next vmexit (whatever > the reason) we will read out whatever changes the guest made to the > debug registers. > > Tested with x86/debug.flat on both Intel and AMD, both direct and > nested virtualization. > > Changes from RFC: changed get_dr7 callback to sync_dirty_debug_regs, > new patches 5-7. > > Paolo Bonzini (7): > KVM: vmx: we do rely on loading DR7 on entry > KVM: x86: change vcpu->arch.switch_db_regs to a bit mask > KVM: x86: Allow the guest to run with dirty debug registers > KVM: vmx: Allow the guest to run with dirty debug registers > KVM: nVMX: Allow nested guests to run with dirty debug registers > KVM: svm: set/clear all DR intercepts in one swoop > KVM: svm: Allow the guest to run with dirty debug registers All patches, Reviewed-by: Radim Krčmář This series is good even without vmcs_{set,clr}_bits(). (There is enough of them already to warrant a cleanup patch.) > > arch/x86/include/asm/kvm_host.h | 8 ++++- > arch/x86/kvm/svm.c | 68 ++++++++++++++++++++++++++++------------- > arch/x86/kvm/vmx.c | 43 ++++++++++++++++++++++++-- > arch/x86/kvm/x86.c | 20 +++++++++++- > 4 files changed, 114 insertions(+), 25 deletions(-) > > -- > 1.8.3.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/