From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932531AbeCMRsK (ORCPT ); Tue, 13 Mar 2018 13:48:10 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:42102 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932302AbeCMRsJ (ORCPT ); Tue, 13 Mar 2018 13:48:09 -0400 From: Vitaly Kuznetsov To: kvm@vger.kernel.org, x86@kernel.org Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski Subject: [PATCH v2 0/2] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Date: Tue, 13 Mar 2018 18:48:03 +0100 Message-Id: <20180313174805.11825-1-vkuznets@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Changes since v1: - Merged patches 1 and 2, skip savesegment() for FS and FS for x86_64 as save_fsgs() already does that [Paolo Bonzini] - Rename save_current_fsgs() -> save_fsgs_for_kvm() [Andy Lutomirski] - Trimmed comments [Andy Lutomirski] - Add Andy's A-b to what is now PATCH2 Some time ago Paolo suggested to take a look at probably unneeded expensive rdmsrs for FS/GS base MSR in vmx_save_host_state(). This is called on every vcpu run when we need to handle vmexit in userspace. vmx_save_host_state() is always called in a very well defined context (ioctl from userspace) so we may try to get the required values for FS/GS bases from in-kernel variables and avoid expensive rdmsrs. My debug shows we're shaving off 240 cpu cycles (E5-2603 v3). Vitaly Kuznetsov (2): x86/kvm/vmx: read MSR_{FS,KERNEL_GS}_BASE from current->thread x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE arch/x86/include/asm/processor.h | 10 ++++++++++ arch/x86/kernel/cpu/common.c | 3 ++- arch/x86/kernel/process_64.c | 14 ++++++++++++++ arch/x86/kvm/vmx.c | 16 ++++++++++++---- 4 files changed, 38 insertions(+), 5 deletions(-) -- 2.14.3