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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 E3877C35DF5 for ; Tue, 25 Feb 2020 06:13:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC31021744 for ; Tue, 25 Feb 2020 06:13:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728955AbgBYGNT (ORCPT ); Tue, 25 Feb 2020 01:13:19 -0500 Received: from mga11.intel.com ([192.55.52.93]:8040 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726421AbgBYGNT (ORCPT ); Tue, 25 Feb 2020 01:13:19 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 24 Feb 2020 22:13:18 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,483,1574150400"; d="scan'208";a="284574425" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by FMSMGA003.fm.intel.com with ESMTP; 24 Feb 2020 22:13:18 -0800 Date: Mon, 24 Feb 2020 22:13:17 -0800 From: Sean Christopherson To: Xiaoyao Li Cc: Vitaly Kuznetsov , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH 1/2] kvm: vmx: Use basic exit reason to check if it's the specific VM EXIT Message-ID: <20200225061317.GV29865@linux.intel.com> References: <20200224020751.1469-1-xiaoyao.li@intel.com> <20200224020751.1469-2-xiaoyao.li@intel.com> <87lfosp9xs.fsf@vitty.brq.redhat.com> <87imjwp24x.fsf@vitty.brq.redhat.com> <20200224161728.GC29865@linux.intel.com> <50134028-ef7a-46c6-7602-095c47406ed7@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50134028-ef7a-46c6-7602-095c47406ed7@intel.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 Tue, Feb 25, 2020 at 08:13:15AM +0800, Xiaoyao Li wrote: > On 2/25/2020 12:17 AM, Sean Christopherson wrote: > >On Mon, Feb 24, 2020 at 02:04:46PM +0100, Vitaly Kuznetsov wrote: > >>Xiaoyao Li writes: > >> > >>>On 2/24/2020 6:16 PM, Vitaly Kuznetsov wrote: > >>>>Xiaoyao Li writes: > >>>> > >>>Here variable basic_exit_reason is added for the cases where only basic > >>>exit reason number is needed. > >>> > >> > >>Can we do the other way around, i.e. introduce 'extended_exit_reason' > >>and use it where all 32 bits are needed? I'm fine with the change, just > >>trying to minimize the (unneeded) code churn. > > > >100% agree. Even better than adding a second field to vcpu_vmx would be > >to make it a union, though we'd probably want to call it something like > >full_exit_reason in that case. That should give us compile-time checks on > >exit_reason, e.g. if we try to query one of the upper bits using a u16, e.g. > > I have thought about union, but it seems > > union { > u16 exit_reason; > u32 full_exit_reason; > } > > is not a good name. Since there are many codes in vmx.c and nested.c assume > that exit_reason stands for 32-bit EXIT REASON vmcs field as well as > evmcs->vm_exit_reason and vmcs12->vm_exit_reason. Do we really want to also > rename them to full_exit_reason? It's actually the opposite, almost all of the VMX code assumes exit_reason holds only the basic exit reason, i.e. a 16-bit value. For example, SGX adds a modifier flag to denote a VM-Exit was from enclave mode, and that bit needs to be stripped from exit_reason, otherwise all the checks like "if (exit_reason == blah_blah_blah)" fail. Making exit_reason a 16-bit alias of the full/extended exit_reason neatly sidesteps that issue. And it is an issue that has caused actual problems in the past, e.g. see commit beb8d93b3e42 ("KVM: VMX: Fix handling of #MC that occurs during VM-Entry"). Coincidentally, that commit also removes a local "u16 basic_exit_reason" :-). Except for one mistake, the pseudo-patch below is the entirety of required changes. Most (all?) of the functions that take "u32 exit_reason" can (and should) continue to take a u32. As for the name, I strongly prefer keeping the exit_reason name for the basic exit reason. The vast majority of VM-Exits do not have modifiers set, i.e. "basic exit reason" == vmcs.EXIT_REASON for nearly all normal usage. This holds true in every form of communication, e.g. when discussing VM-Exit reasons, it's never qualified with "basic", it's simply the exit reason. IMO the code is better off following the colloquial usage of "exit reason". A simple comment above the union would suffice to clear up any confusion with respect to the SDM. > Maybe we name it > > union { > u16 basic_exit_reason; > u32 exit_reason; > } > > as what SDM defines? > > >--- a/arch/x86/kvm/vmx/vmx.c > >+++ b/arch/x86/kvm/vmx/vmx.c > >@@ -5818,7 +5818,7 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, > > if (is_guest_mode(vcpu) && nested_vmx_exit_reflected(vcpu, exit_reason)) > > return nested_vmx_reflect_vmexit(vcpu, exit_reason); > > > >- if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) { > >+ if (vmx->full_exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) { If we do go the union route, this snippet of code is insufficient, the full/extended exit reason needs to be snapshotted early for use in the tracepoint and in fail_entry.hardware_entry_failure_reason. > > dump_vmcs(); > > vcpu->run->exit_reason = KVM_EXIT_FAIL_ENTRY; > > vcpu->run->fail_entry.hardware_entry_failure_reason > >@@ -6620,11 +6620,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu) > > vmx->nested.nested_run_pending = 0; > > vmx->idt_vectoring_info = 0; > > > >- vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON); > >- if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY) > >+ vmx->full_exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON); > >+ if (vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY) > > kvm_machine_check(); > > > >- if (vmx->fail || (vmx->exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY)) > >+ if (vmx->fail || > >+ (vmx->full_exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY)) > > return; > > > > vmx->loaded_vmcs->launched = 1; > >diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h > >index 7f42cf3dcd70..60c09640ea59 100644 > >--- a/arch/x86/kvm/vmx/vmx.h > >+++ b/arch/x86/kvm/vmx/vmx.h > >@@ -260,7 +260,10 @@ struct vcpu_vmx { > > int vpid; > > bool emulation_required; > > > >- u32 exit_reason; > >+ union { > >+ u16 exit_reason; > >+ u32 full_exit_reason; > >+ } > > > > /* Posted interrupt descriptor */ > > struct pi_desc pi_desc; > > > > > > > > > > > >>-- > >>Vitaly > >> >