From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77D01C32792 for ; Mon, 30 Sep 2019 15:19:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 571212168B for ; Mon, 30 Sep 2019 15:19:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731921AbfI3PTq (ORCPT ); Mon, 30 Sep 2019 11:19:46 -0400 Received: from mga07.intel.com ([134.134.136.100]:6202 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730809AbfI3PTq (ORCPT ); Mon, 30 Sep 2019 11:19:46 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Sep 2019 08:19:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,567,1559545200"; d="scan'208";a="195352698" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by orsmga006.jf.intel.com with ESMTP; 30 Sep 2019 08:19:45 -0700 Date: Mon, 30 Sep 2019 08:19:45 -0700 From: Sean Christopherson To: Vitaly Kuznetsov Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Reto Buerki , Liran Alon Subject: Re: [PATCH v2 4/8] KVM: VMX: Optimize vmx_set_rflags() for unrestricted guest Message-ID: <20190930151945.GB14693@linux.intel.com> References: <20190927214523.3376-1-sean.j.christopherson@intel.com> <20190927214523.3376-5-sean.j.christopherson@intel.com> <87muem40wi.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87muem40wi.fsf@vitty.brq.redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 30, 2019 at 10:57:17AM +0200, Vitaly Kuznetsov wrote: > Sean Christopherson writes: > > > Rework vmx_set_rflags() to avoid the extra code need to handle emulation > > of real mode and invalid state when unrestricted guest is disabled. The > > primary reason for doing so is to avoid the call to vmx_get_rflags(), > > which will incur a VMREAD when RFLAGS is not already available. When > > running nested VMs, the majority of calls to vmx_set_rflags() will occur > > without an associated vmx_get_rflags(), i.e. when stuffing GUEST_RFLAGS > > during transitions between vmcs01 and vmcs02. > > > > Note, vmx_get_rflags() guarantees RFLAGS is marked available. > > > > Signed-off-by: Sean Christopherson > > --- > > arch/x86/kvm/vmx/vmx.c | 28 ++++++++++++++++++---------- > > 1 file changed, 18 insertions(+), 10 deletions(-) > > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index 83fe8b02b732..814d3e6d0264 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -1426,18 +1426,26 @@ unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu) > > void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags) > > { > > struct vcpu_vmx *vmx = to_vmx(vcpu); > > - unsigned long old_rflags = vmx_get_rflags(vcpu); > > + unsigned long old_rflags; > > > > - __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail); > > - vmx->rflags = rflags; > > - if (vmx->rmode.vm86_active) { > > - vmx->rmode.save_rflags = rflags; > > - rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM; > > + if (enable_unrestricted_guest) { > > + __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail); > > + > > + vmx->rflags = rflags; > > + vmcs_writel(GUEST_RFLAGS, rflags); > > + } else { > > + old_rflags = vmx_get_rflags(vcpu); > > + > > + vmx->rflags = rflags; > > + if (vmx->rmode.vm86_active) { > > + vmx->rmode.save_rflags = rflags; > > + rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM; > > + } > > + vmcs_writel(GUEST_RFLAGS, rflags); > > + > > + if ((old_rflags ^ vmx->rflags) & X86_EFLAGS_VM) > > + vmx->emulation_required = emulation_required(vcpu); > > } > > - vmcs_writel(GUEST_RFLAGS, rflags); > > We're doing vmcs_writel() in both branches so it could've stayed here, right? Yes, but the resulting code is a bit ugly. emulation_required() consumes vmcs.GUEST_RFLAGS, i.e. the if statement that reads old_rflags would also need to be outside of the else{} case. This isn't too bad: if (!enable_unrestricted_guest && ((old_rflags ^ vmx->rflags) & X86_EFLAGS_VM)) vmx->emulation_required = emulation_required(vcpu); but gcc isn't smart enough to understand old_rflags won't be used if enable_unrestricted_guest, so old_rflags either needs to be tagged with uninitialized_var() or explicitly initialized in the if(){} case. Duplicating a small amount of code felt like the lesser of two evils. > > - > > - if ((old_rflags ^ vmx->rflags) & X86_EFLAGS_VM) > > - vmx->emulation_required = emulation_required(vcpu); > > } > > > > u32 vmx_get_interrupt_shadow(struct kvm_vcpu *vcpu) > > Reviewed-by: Vitaly Kuznetsov > > -- > Vitaly