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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 429B8C43219 for ; Tue, 30 Apr 2019 20:19:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1702B20652 for ; Tue, 30 Apr 2019 20:19:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726105AbfD3UTp (ORCPT ); Tue, 30 Apr 2019 16:19:45 -0400 Received: from mga17.intel.com ([192.55.52.151]:12514 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726024AbfD3UTo (ORCPT ); Tue, 30 Apr 2019 16:19:44 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 30 Apr 2019 13:19:44 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,414,1549958400"; d="scan'208";a="342226031" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.181]) by fmsmga005.fm.intel.com with ESMTP; 30 Apr 2019 13:19:44 -0700 Date: Tue, 30 Apr 2019 13:19:43 -0700 From: Sean Christopherson To: Paolo Bonzini Cc: Radim =?utf-8?B?S3LEjW3DocWZ?= , Joerg Roedel , kvm@vger.kernel.org Subject: Re: [PATCH 0/3] KVM: x86: Drop "caching" of always-available GPRs Message-ID: <20190430201943.GA4868@linux.intel.com> References: <20190430173619.15774-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Tue, Apr 30, 2019 at 10:03:59PM +0200, Paolo Bonzini wrote: > On 30/04/19 19:36, Sean Christopherson wrote: > > KVM's GPR caching logic is unconditionally emitted for all GPR accesses > > (that go through the accessors), even when the register being accessed > > is fixed and always available. This bloats KVM due to the instructions > > needed to test and set the available/dirty bitmaps, and to conditionally > > invoke the .cache_reg() callback. The latter is especially painful when > > compiling with retpolines. > > > > Eliminate the unnecessary overhead by: > > > > - Adding dedicated accessors for every GPR > > - Omitting the caching logic for GPRs that are always available > > - Preventing use of the unoptimized versions for fixed accesses > > > > The last patch is an opportunistic clean up of VMX, which has gradually > > acquired a bad habit of sprinkling in direct access to GPRs. > > Another related cleanup is to replace these with the direct accessors: > > arch/x86/kvm/vmx/nested.c: vmcs12->guest_rsp = kvm_register_read(vcpu, VCPU_REGS_RSP); > arch/x86/kvm/vmx/nested.c: vmcs12->guest_rip = kvm_register_read(vcpu, VCPU_REGS_RIP); > arch/x86/kvm/x86.c: regs->rsp = kvm_register_read(vcpu, VCPU_REGS_RSP); > arch/x86/kvm/svm.c: kvm_register_write(&svm->vcpu, VCPU_REGS_RSP, hsave->save.rsp); > arch/x86/kvm/svm.c: kvm_register_write(&svm->vcpu, VCPU_REGS_RIP, hsave->save.rip); > arch/x86/kvm/svm.c: kvm_register_write(&svm->vcpu, VCPU_REGS_RSP, nested_vmcb->save.rsp); > arch/x86/kvm/svm.c: kvm_register_write(&svm->vcpu, VCPU_REGS_RIP, nested_vmcb->save.rip); > arch/x86/kvm/vmx/nested.c: kvm_register_write(vcpu, VCPU_REGS_RSP, vmcs12->guest_rsp); > arch/x86/kvm/vmx/nested.c: kvm_register_write(vcpu, VCPU_REGS_RIP, vmcs12->guest_rip); > arch/x86/kvm/vmx/nested.c: kvm_register_write(vcpu, VCPU_REGS_RSP, vmcs12->host_rsp); > arch/x86/kvm/vmx/nested.c: kvm_register_write(vcpu, VCPU_REGS_RIP, vmcs12->host_rip); > arch/x86/kvm/x86.c: kvm_register_write(vcpu, VCPU_REGS_RSP, regs->rsp); > > I can take care of this. I have applied patches 1 and 3. I didn't apply > patch 2 for the reasons I mentioned in my reply, and because I am not sure > if it works properly---it should have flagged the above occurrences, > shouldn't it? I squeezed the cleanup into patch 2. I should have called that out in the changelog but didn't for whatever reason. Probably would have been even better to do the refactor in a separate patch. Sorry :(