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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 2722EC433E0 for ; Tue, 2 Feb 2021 22:41:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C977F64F68 for ; Tue, 2 Feb 2021 22:41:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235561AbhBBWlu (ORCPT ); Tue, 2 Feb 2021 17:41:50 -0500 Received: from mail.kernel.org ([198.145.29.99]:43318 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234135AbhBBWlt (ORCPT ); Tue, 2 Feb 2021 17:41:49 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5B6AC64F68; Tue, 2 Feb 2021 22:41:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612305667; bh=bhanN5du/Uw41D7LIvrjljn0saroYLL1UQvTM6/jgbk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Og8kB+9e7Ji7BlPRG6CvYKz2egn/yVSkw4NGkZrtfVG34MN5wnyFsA5yAgpDdyDYZ g2iJdr6bpJujA/f84vmSZ0eNmYbBCYwFuCBoWM7b+6cLkyjogWHQERjfrq2bfzWIs/ DqLZ5w+ONdss2lzqXJxAiNpjILD2/GEktKJURiGBNsuSPM82eSGHmrCMjA1Da9zNjY rSkGpjRQixSDiQ1V9DaTwhxLgSuSnaYrPeRjlL7/JlZLk/SXkcNhK7LNsaEJo5iiS3 Rt8tSQfEoOMWA0gA4jNMSuTkfQKQMfSqg3k1TwSW++D33F7ivedqYaJ/BWUitgJCFj yNzB51EV83BcQ== Date: Wed, 3 Feb 2021 00:41:00 +0200 From: Jarkko Sakkinen To: Kai Huang Cc: linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, seanjc@google.com, luto@kernel.org, dave.hansen@intel.com, haitao.huang@intel.com, pbonzini@redhat.com, bp@alien8.de, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, jmattson@google.com, joro@8bytes.org, vkuznets@redhat.com, wanpengli@tencent.com Subject: Re: [RFC PATCH v3 16/27] KVM: VMX: Convert vcpu_vmx.exit_reason to a union Message-ID: References: <20210201133259.e0398c9f0b229fd79a8c16c6@intel.com> <20210203082340.e808a4d97318e07b265d0326@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203082340.e808a4d97318e07b265d0326@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Wed, Feb 03, 2021 at 08:23:40AM +1300, Kai Huang wrote: > On Tue, 2 Feb 2021 19:24:42 +0200 Jarkko Sakkinen wrote: > > On Mon, Feb 01, 2021 at 01:32:59PM +1300, Kai Huang wrote: > > > On Sat, 30 Jan 2021 17:00:46 +0200 Jarkko Sakkinen wrote: > > > > On Tue, Jan 26, 2021 at 10:31:37PM +1300, Kai Huang wrote: > > > > > From: Sean Christopherson > > > > > > > > > > Convert vcpu_vmx.exit_reason from a u32 to a union (of size u32). The > > > > > full VM_EXIT_REASON field is comprised of a 16-bit basic exit reason in > > > > > bits 15:0, and single-bit modifiers in bits 31:16. > > > > > > > > > > Historically, KVM has only had to worry about handling the "failed > > > > > VM-Entry" modifier, which could only be set in very specific flows and > > > > > required dedicated handling. I.e. manually stripping the FAILED_VMENTRY > > > > > bit was a somewhat viable approach. But even with only a single bit to > > > > > worry about, KVM has had several bugs related to comparing a basic exit > > > > > reason against the full exit reason store in vcpu_vmx. > > > > > > > > > > Upcoming Intel features, e.g. SGX, will add new modifier bits that can > > > > BTW, SGX is not an upcoming CPU feature. > > Probably Sean was implying: "Upcoming CPU features that will be supported by > Linux". I don't see big deal here. > > > > > Also, broadly speaking of upcoming features is not right thing to do. > > Better just to scope this down SGX. Theoretically upcoming CPU features > > can do pretty much anything. This is change is first and foremost done > > for SGX. > > > > > > > be set on more or less any VM-Exit, as opposed to the significantly more > > > > > restricted FAILED_VMENTRY, i.e. correctly handling everything in one-off > > > > > flows isn't scalable. Tracking exit reason in a union forces code to > > > > > explicitly choose between consuming the full exit reason and the basic > > > > > exit, and is a convenient way to document and access the modifiers. > > > > > > > > I *believe* that the change is correct but I dropped in the last paragraph > > > > - most likely only because of lack of expertise in this area. > > > > > > > > I ask the most basic question: why SGX will add new modifier bits? > > > > > > Not 100% sure about your question. Assuming you are asking SGX hardware > > > behavior, SGX architecture adds a new modifier bit (27) to Exit Reason, similar > > > to new #PF.SGX bit. > > > > > > Please refer to SDM Volume 3, Chapter 27.2.1 Basic VM-Exit Information. > > > > > > Sean's commit msg already provides significant motivation of the change in this > > > patch. > > > > Just describe why SGX requires this. That's all. > > This patch is to change vmexit info from u32 to union, because at least one > additional modifier is going to be added, due to SGX. So the motivation of this > patch is the fact that "one or more additional modifier bits will be added", > and SGX is just example. > > So I don't think adding too much SGX backgroud in *THIS* patch is needed. > And another patch: > > [RFC PATCH v3 21/27] KVM: VMX: Add basic handling of VM-Exit from SGX enclave > > already has enough information of "why new modifier bit is aadded for SGX". > Sean also replied to you. Well it comes after this patch. So you either need to provide the context here or reorder patches. If latter is impossible, I would just add those couple of paragraphs that Sean wrote. > Please look at that patch and see whether it satisfies you. Well there needs to be causality in patches. I should be able to review the patches if 17-> did not exist. > > > > > /Jarkko > /Jarkko