From patchwork Fri Jan 18 21:20:10 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 10771555 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C85AF139A for ; Fri, 18 Jan 2019 21:22:32 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id B7C0A30599 for ; Fri, 18 Jan 2019 21:22:32 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B627D305F5; Fri, 18 Jan 2019 21:22:32 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4558430599 for ; Fri, 18 Jan 2019 21:22:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729704AbfARVWI (ORCPT ); Fri, 18 Jan 2019 16:22:08 -0500 Received: from mga05.intel.com ([192.55.52.43]:43594 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729628AbfARVWF (ORCPT ); Fri, 18 Jan 2019 16:22:05 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Jan 2019 13:22:04 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,492,1539673200"; d="scan'208";a="139511457" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.14]) by fmsmga001.fm.intel.com with ESMTP; 18 Jan 2019 13:22:04 -0800 From: Sean Christopherson To: Paolo Bonzini , =?utf-8?b?UmFkaW0gS3LEjW3DocWZ?= Cc: kvm@vger.kernel.org, Andi Kleen , Josh Poimboeuf Subject: [PATCH 02/29] KVM: nVMX: Check a single byte for VMCS "launched" in nested early checks Date: Fri, 18 Jan 2019 13:20:10 -0800 Message-Id: <20190118212037.24412-3-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190118212037.24412-1-sean.j.christopherson@intel.com> References: <20190118212037.24412-1-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 X-Virus-Scanned: ClamAV using ClamSMTP Nested early checks does a manual comparison of a VMCS' launched status in its asm blob to execute the correct VM-Enter instruction, i.e. VMLAUNCH vs. VMRESUME. The launched flag is a bool, which is a typedef of _Bool. C99 does not define an exact size for _Bool, stating only that is must be large enough to hold '0' and '1'. Most, if not all, compilers use a single byte for _Bool, including gcc[1]. The use of 'cmpl' instead of 'cmpb' was not deliberate, but rather the result of a copy-paste as the asm blob was directly derived from the asm blob for vCPU-run. This has not caused any known problems, likely due to compilers aligning variables to 4-byte or 8-byte boundaries and KVM zeroing out struct vcpu_vmx during allocation. I.e. vCPU-run accesses "junk" data, it just happens to always be zero and so doesn't affect the result. [1] https://gcc.gnu.org/ml/gcc-patches/2000-10/msg01127.html Fixes: 52017608da33 ("KVM: nVMX: add option to perform early consistency checks via H/W") Cc: Signed-off-by: Sean Christopherson Reviewed-by: Jim Mattson Reviewed-by: Konrad Rzeszutek Wilk --- arch/x86/kvm/vmx/nested.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 3170e291215d..69920c2fa5db 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2760,7 +2760,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu) "add $%c[wordsize], %%" _ASM_SP "\n\t" /* un-adjust RSP */ /* Check if vmlaunch or vmresume is needed */ - "cmpl $0, %c[launched](%% " _ASM_CX")\n\t" + "cmpb $0, %c[launched](%% " _ASM_CX")\n\t" "call vmx_vmenter\n\t"