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=-7.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, HK_RANDOM_FROM,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 95F8CC3F2CD for ; Tue, 3 Mar 2020 04:02:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 678D62465D for ; Tue, 3 Mar 2020 04:02:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727075AbgCCECq (ORCPT ); Mon, 2 Mar 2020 23:02:46 -0500 Received: from mga18.intel.com ([134.134.136.126]:31538 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726910AbgCCECq (ORCPT ); Mon, 2 Mar 2020 23:02:46 -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 orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Mar 2020 20:02:44 -0800 X-IronPort-AV: E=Sophos;i="5.70,510,1574150400"; d="scan'208";a="233458070" 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 20:02:42 -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> From: Xiaoyao Li Message-ID: Date: Tue, 3 Mar 2020 12:02:39 +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: <20200303034532.GC27842@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 11:45 AM, Sean Christopherson wrote: > On Tue, Mar 03, 2020 at 10:27:47AM +0800, Xiaoyao Li wrote: >> On 3/3/2020 4:49 AM, Sean Christopherson wrote: >>> On Mon, Mar 02, 2020 at 09:26:54PM +0100, Jan Kiszka wrote: >>>> On 02.03.20 20:57, Sean Christopherson wrote: >>>>> Rework kvm_cpuid() to query entry->function when adjusting the output >>>>> values so that the original function (in the aptly named "function") is >>>>> preserved for tracing. This fixes a bug where trace_kvm_cpuid() will >>>>> trace the max function for a range instead of the requested function if >>>>> the requested function is out-of-range and an entry for the max function >>>>> exists. >>>>> >>>>> Fixes: 43561123ab37 ("kvm: x86: Improve emulation of CPUID leaves 0BH and 1FH") >>>>> Reported-by: Jan Kiszka >>>>> Cc: Jim Mattson >>>>> Cc: Xiaoyao Li >>>>> Signed-off-by: Sean Christopherson >>>>> --- >>>>> arch/x86/kvm/cpuid.c | 15 +++++++-------- >>>>> 1 file changed, 7 insertions(+), 8 deletions(-) >>>>> >>>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c >>>>> index b1c469446b07..6be012937eba 100644 >>>>> --- a/arch/x86/kvm/cpuid.c >>>>> +++ b/arch/x86/kvm/cpuid.c >>>>> @@ -997,12 +997,12 @@ static bool cpuid_function_in_range(struct kvm_vcpu *vcpu, u32 function) >>>>> return max && function <= max->eax; >>>>> } >>>>> +/* Returns true if the requested leaf/function exists in guest CPUID. */ >>>>> bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >>>>> u32 *ecx, u32 *edx, bool check_limit) >>>>> { >>>>> - u32 function = *eax, index = *ecx; >>>>> + const u32 function = *eax, index = *ecx; >>>>> struct kvm_cpuid_entry2 *entry; >>>>> - struct kvm_cpuid_entry2 *max; >>>>> bool found; >>>>> entry = kvm_find_cpuid_entry(vcpu, function, index); >>>>> @@ -1015,18 +1015,17 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, >>>>> */ >>>>> if (!entry && check_limit && !guest_cpuid_is_amd(vcpu) && >>>>> !cpuid_function_in_range(vcpu, function)) { >>>>> - max = kvm_find_cpuid_entry(vcpu, 0, 0); >>>>> - if (max) { >>>>> - function = max->eax; >>>>> - entry = kvm_find_cpuid_entry(vcpu, function, index); >>>>> - } >>>>> + entry = kvm_find_cpuid_entry(vcpu, 0, 0); >>>>> + if (entry) >>>>> + entry = kvm_find_cpuid_entry(vcpu, entry->eax, index); >>>>> } >>>>> if (entry) { >>>>> *eax = entry->eax; >>>>> *ebx = entry->ebx; >>>>> *ecx = entry->ecx; >>>>> *edx = entry->edx; >>>>> - if (function == 7 && index == 0) { >>>>> + >>>>> + if (entry->function == 7 && index == 0) { >>>>> u64 data; >>>>> if (!__kvm_get_msr(vcpu, MSR_IA32_TSX_CTRL, &data, true) && >>>>> (data & TSX_CTRL_CPUID_CLEAR)) >>>>> >>>> >>>> What about the !entry case below this? It was impacted by the function >>>> capping so far, not it's no longer. >>> >>> Hmm, the only way the output would be different is in a really contrived >>> scenario where userspace doesn't provide an entry for the max basic leaf. >>> >>> The !entry path can only be reached with "orig_function != function" if >>> orig_function is out of range and there is no entry for the max basic leaf. >> >>> The adjustments for 0xb/0x1f require the max basic leaf to be 0xb or 0x1f, >>> and to take effect with !entry would require there to be a CPUID.max.1 but >>> not a CPUID.max.0. That'd be a violation of Intel's SDM, i.e. it's bogus >>> userspace input and IMO can be ignored. >>> >> >> 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.