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=-1.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A9C15C3F2C6 for ; Tue, 3 Mar 2020 04:30:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 79D9C20716 for ; Tue, 3 Mar 2020 04:30:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727363AbgCCEaZ (ORCPT ); Mon, 2 Mar 2020 23:30:25 -0500 Received: from mga02.intel.com ([134.134.136.20]:41435 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726974AbgCCEaZ (ORCPT ); Mon, 2 Mar 2020 23:30:25 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Mar 2020 20:30:24 -0800 X-IronPort-AV: E=Sophos;i="5.70,510,1574150400"; d="scan'208";a="233478293" Received: from xiaoyaol-mobl.ccr.corp.intel.com (HELO [10.255.30.67]) ([10.255.30.67]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-SHA; 02 Mar 2020 20:30:21 -0800 Subject: Re: [PATCH 1/6] KVM: x86: Fix tracing of CPUID.function when function is out-of-range To: Sean Christopherson Cc: Jan Kiszka , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200302195736.24777-1-sean.j.christopherson@intel.com> <20200302195736.24777-2-sean.j.christopherson@intel.com> <188dc96a-6a3b-4021-061a-0f11cbb9f177@siemens.com> <20200302204940.GG6244@linux.intel.com> <16e902a8-7883-0b67-d4ee-73e8fe22f955@intel.com> <20200303034532.GC27842@linux.intel.com> <20200303041208.GE27842@linux.intel.com> From: Xiaoyao Li Message-ID: <331345c6-d3c1-5052-d59c-36349b8b0df6@intel.com> Date: Tue, 3 Mar 2020 12:30:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200303041208.GE27842@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/3/2020 12:12 PM, Sean Christopherson wrote: > On Tue, Mar 03, 2020 at 12:02:39PM +0800, Xiaoyao Li wrote: >> On 3/3/2020 11:45 AM, Sean Christopherson wrote: >>> On Tue, Mar 03, 2020 at 10:27:47AM +0800, Xiaoyao Li wrote: >>>> Sorry I cannot catch you. Why it's a violation of Intel's SDM? >>> >>> The case being discussed above would look like: >>> >>> KVM CPUID Entries: >>> Function Index Output >>> 0x00000000 0x00: eax=0x0000000b ebx=0x756e6547 ecx=0x6c65746e edx=0x49656e69 >>> 0x00000001 0x00: eax=0x000906ea ebx=0x03000800 ecx=0xfffa3223 edx=0x0f8bfbff >>> 0x00000002 0x00: eax=0x00000001 ebx=0x00000000 ecx=0x0000004d edx=0x002c307d >>> 0x00000003 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 >>> 0x00000004 0x00: eax=0x00000121 ebx=0x01c0003f ecx=0x0000003f edx=0x00000001 >>> 0x00000004 0x01: eax=0x00000122 ebx=0x01c0003f ecx=0x0000003f edx=0x00000001 >>> 0x00000004 0x02: eax=0x00000143 ebx=0x03c0003f ecx=0x00000fff edx=0x00000001 >>> 0x00000004 0x03: eax=0x00000163 ebx=0x03c0003f ecx=0x00003fff edx=0x00000006 >>> 0x00000005 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000003 edx=0x00000000 >>> 0x00000006 0x00: eax=0x00000004 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 >>> 0x00000007 0x00: eax=0x00000000 ebx=0x009c4fbb ecx=0x00000004 edx=0x84000000 >>> 0x00000008 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 >>> 0x00000009 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 >>> 0x0000000a 0x00: eax=0x07300402 ebx=0x00000000 ecx=0x00000000 edx=0x00000603 >>> --> MISSING CPUID.0xB.0 >>> 0x0000000b 0x01: eax=0x00000000 ebx=0x00000001 ecx=0x00000201 edx=0x00000003 >>> >>> CPUID.0xB.0 does not exist, so output.ECX=0, which indicates an invalid >>> level-type. >>> >>> The SDM states (for CPUID.0xB): >>> >>> If an input value n in ECX returns the invalid level-type of 0 in ECX[15:8], >>> other input values with ECX > n also return 0 in ECX[15:8] >>> >>> That means returning a valid level-type in CPUID.0xB.1 as above violates >>> the SDM's definition of how leaf 0xB works. I'm arguing we can ignore the >>> adjustments that would be done on output.E{C,D} for an out of range leaf >>> because the model is bogus. >> >> Right. >> >> So we'd better do something in KVM_SET_CPUID* , to avoid userspace set bogus >> cpuid. >> >>>> Supposing the max basic is 0x1f, and it queries cpuid(0x20, 0x5), >>>> it should return cpuid(0x1f, 0x5). >>>> >>>> But based on this patch, it returns all zeros. >>> >>> Have you tested the patch, or is your comment based on the above discussion >>> and/or code inspection? Honest question, because I've thoroughly tested >>> the above scenario and it works as you describe, but now I'm worried I >>> completely botched my testing. >>> >> >> No, I didn't test. >> >> Leaf 0xB and 0x1f are special cases when they are the maximum basic leaf, >> because no matter what subleaf is, there is always a non-zero E[CX,DX]. >> >> If cpuid.0 returns maximum basic leaf as 0xB/0x1F, when queried leaf is >> greater, it should always return a non-zero value. > > Yes, and that's userspace's responsibility to not screw up. E.g. if > userspace didn't create CPUID.0xB.0 (as above) then it's not KVM's fault > for returning zeros when the guest executes CPUID.0xB.0. > But this needs userspace to create all the subleaf of 0xB/0x1F. with a correct userspace, for example, it only creates one more subleaf of 0xB/0x1F to indicate from this subleaf, no valid level-type anymore. So when maximum basic leaf is 0x1f, cpuid(0x20, bigger than the first invalid subleaf created by userspace) returns all-zero.