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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 B07CFC3F2C6 for ; Tue, 3 Mar 2020 03:45:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8EBBF20848 for ; Tue, 3 Mar 2020 03:45:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726992AbgCCDpe (ORCPT ); Mon, 2 Mar 2020 22:45:34 -0500 Received: from mga11.intel.com ([192.55.52.93]:16934 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726843AbgCCDpd (ORCPT ); Mon, 2 Mar 2020 22:45:33 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga102.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 02 Mar 2020 19:45:32 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,509,1574150400"; d="scan'208";a="351725731" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga001.fm.intel.com with ESMTP; 02 Mar 2020 19:45:32 -0800 Date: Mon, 2 Mar 2020 19:45:32 -0800 From: Sean Christopherson To: Xiaoyao Li Cc: Jan Kiszka , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/6] KVM: x86: Fix tracing of CPUID.function when function is out-of-range Message-ID: <20200303034532.GC27842@linux.intel.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <16e902a8-7883-0b67-d4ee-73e8fe22f955@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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.