From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751984AbeCLODG (ORCPT ); Mon, 12 Mar 2018 10:03:06 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:45850 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751252AbeCLODD (ORCPT ); Mon, 12 Mar 2018 10:03:03 -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 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Date: Mon, 12 Mar 2018 15:02:57 +0100 Message-Id: <20180312140300.6166-1-vkuznets@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Changes since RFC [Andy Lutomirski]: - Export new save_current_fsgs() API and call it before reading current->thread.fs/gsbase - New cpu_kernelmode_gs_base() API. - Some comments added. 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 (3): x86/kvm/vmx: read MSR_FS_BASE from current->thread x86/kvm/vmx: read MSR_KERNEL_GS_BASE from current->thread x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE arch/x86/include/asm/processor.h | 8 ++++++++ arch/x86/kernel/cpu/common.c | 3 ++- arch/x86/kernel/process_64.c | 20 ++++++++++++++++++++ arch/x86/kvm/vmx.c | 9 ++++++--- 4 files changed, 36 insertions(+), 4 deletions(-) -- 2.14.3