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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL 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 82858C433E6 for ; Tue, 9 Mar 2021 19:47:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 549876523D for ; Tue, 9 Mar 2021 19:47:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231226AbhCITq5 (ORCPT ); Tue, 9 Mar 2021 14:46:57 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229948AbhCITq0 (ORCPT ); Tue, 9 Mar 2021 14:46:26 -0500 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 25F0EC06174A for ; Tue, 9 Mar 2021 11:46:26 -0800 (PST) Received: by mail-pg1-x529.google.com with SMTP id w34so8444878pga.8 for ; Tue, 09 Mar 2021 11:46:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=ulHEFS0WTjr5/aHH5c5+5bv6zMRwJNOuuyKVe1EaduU=; b=tDCwz+0VAHUWFW8ENdoYvwCgB+PYV8SZx1symQ5stezY2HKO9bhjTb9is7Do0Rmyrz RKwPLyYnSl04hTUWb+W/puDN2woRhrGNiDr/lkrXFKTgTIalcMFdNeAwQqG+6eizJbvq YPwNe32v9Zi16DZf5EWTcqJGrRh5QjBxcOHr/AVOfJtL2bAiLUPF226M1nJO7uDVKb3q v2Cx+aSAk4qegAHMZ18LAEuEqVVLCkAnHnXGo0pKf+5ko5KET2Ah+cKgosInrny4Yxt5 07Bg8cjHjOFqXB0pn/YDutiqlhkxwHnpiHperOAFw15MhS/tax2G35tE1Lrp6mnjEZ5P S7Iw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=ulHEFS0WTjr5/aHH5c5+5bv6zMRwJNOuuyKVe1EaduU=; b=kHIDni8K50AvUdi86TbD4OYMf5vFqPJ3uoFtW/6+nwJSqXBlRrozcVMsxtBL2OdGvO UlQ9GiP0PI5kh4ehzJzoD8s0Au2fs89MHXcbSuPZ7qNAX/GUbAybDQndYfCcRgkrZGam hni8xgytGmdxHC1WL7N2KbNBv5Ck5u6muDHaq44jit0iSjgVgLvCx4BZoQvLIeH2UoXe 0StKnIVjOPS9Kq2SkVzZF/xRQS5JktvA46foLgI4H8q3x4xhnfX4ZvmSMShwNkfq6sij sduGEodS+bUH3SS7qjJW5m46zlZvHpCpYLvnfYFnYXztiQEcN4FdBsQH6iRdVVGrU8r+ cccA== X-Gm-Message-State: AOAM5314tBuVNACDro63jZGbW1nTRRKeg5C/2ZYxFnD+xxriR4JsMZJV gOrpKk+dX0Nn5IjvLkJDphY/6Q== X-Google-Smtp-Source: ABdhPJybHTP3N7F5degWWSVA3xCblaZEqgKqapj1rEhqdWEkirSEOr0Ufvmn/BzU4CJTGAWgpJgQQg== X-Received: by 2002:a62:7a09:0:b029:1f1:5cf4:3fd7 with SMTP id v9-20020a627a090000b02901f15cf43fd7mr4818201pfc.66.1615319185563; Tue, 09 Mar 2021 11:46:25 -0800 (PST) Received: from google.com ([2620:15c:f:10:e4dd:6c31:9463:f8da]) by smtp.gmail.com with ESMTPSA id e63sm5677664pfe.208.2021.03.09.11.46.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Mar 2021 11:46:24 -0800 (PST) Date: Tue, 9 Mar 2021 11:46:18 -0800 From: Sean Christopherson To: Jim Mattson Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Thomas Gleixner , Borislav Petkov , the arch/x86 maintainers , Paolo Bonzini , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Joerg Roedel , LKML , kvm list , Like Xu , Dmitry Vyukov , syzbot+cce9ef2dd25246f815ee@syzkaller.appspotmail.com Subject: Re: [PATCH v2] x86/perf: Use RET0 as default for guest_get_msrs to handle "no PMU" case Message-ID: References: <20210309171019.1125243-1-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Mar 09, 2021, Jim Mattson wrote: > On Tue, Mar 9, 2021 at 9:10 AM Sean Christopherson > wrote: > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index 50810d471462..32cf8287d4a7 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -6580,8 +6580,8 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx > > *vmx) > > int i, nr_msrs; > > struct perf_guest_switch_msr *msrs; > > > > + /* Note, nr_msrs may be garbage if perf_guest_get_msrs() returns > > NULL. */ > > > > You could drop the scary comment with a profligate initialization of > nr_msrs to 0. Yeah, I considered that as well. I opted for the scary comment because I wanted to dissuade future patches from modifying this code without taking into account the non-obvious behavior.