From patchwork Wed Dec 11 17:58:21 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 11285895 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 00BC114B7 for ; Wed, 11 Dec 2019 17:58:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DE99E24653 for ; Wed, 11 Dec 2019 17:58:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730970AbfLKR6Y (ORCPT ); Wed, 11 Dec 2019 12:58:24 -0500 Received: from mga02.intel.com ([134.134.136.20]:29189 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730918AbfLKR6X (ORCPT ); Wed, 11 Dec 2019 12:58:23 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Dec 2019 09:58:22 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,302,1571727600"; d="scan'208";a="203645151" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.202]) by orsmga007.jf.intel.com with ESMTP; 11 Dec 2019 09:58:22 -0800 From: Sean Christopherson To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 1/2] KVM: x86: Add build-time assertion on usage of bit() Date: Wed, 11 Dec 2019 09:58:21 -0800 Message-Id: <20191211175822.1925-2-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191211175822.1925-1-sean.j.christopherson@intel.com> References: <20191211175822.1925-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Add build-time checks to ensure KVM isn't trying to do a reverse CPUID lookup on Linux-defined feature bits, along with comments to explain the gory details of X86_FEATUREs and bit(). Signed-off-by: Sean Christopherson --- Note, the premature newline in the first line of the second comment is intentional to reduce churn in the next patch. arch/x86/kvm/x86.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index cab5e71f0f0f..4ee4175c66a7 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -144,9 +144,28 @@ static inline bool is_pae_paging(struct kvm_vcpu *vcpu) return !is_long_mode(vcpu) && is_pae(vcpu) && is_paging(vcpu); } -static inline u32 bit(int bitno) +/* + * Retrieve the bit mask from an X86_FEATURE_* definition. Features contain + * the hardware defined bit number (stored in bits 4:0) and a software defined + * "word" (stored in bits 31:5). The word is used to index into arrays of + * bit masks that hold the per-cpu feature capabilities, e.g. this_cpu_has(). + */ +static __always_inline u32 bit(int feature) { - return 1 << (bitno & 31); + /* + * bit() is intended to be used only for hardware-defined + * words, i.e. words whose bits directly correspond to a CPUID leaf. + * Retrieving the bit mask from a Linux-defined word is nonsensical + * as the bit number/mask is an arbitrary software-defined value and + * can't be used by KVM to query/control guest capabilities. + */ + BUILD_BUG_ON((feature >> 5) == CPUID_LNX_1); + BUILD_BUG_ON((feature >> 5) == CPUID_LNX_2); + BUILD_BUG_ON((feature >> 5) == CPUID_LNX_3); + BUILD_BUG_ON((feature >> 5) == CPUID_LNX_4); + BUILD_BUG_ON((feature >> 5) > CPUID_7_EDX); + + return 1 << (feature & 31); } static inline u8 vcpu_virt_addr_bits(struct kvm_vcpu *vcpu)