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=-10.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 BF2E0C4CEC7 for ; Fri, 13 Sep 2019 13:31:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 92996206A5 for ; Fri, 13 Sep 2019 13:31:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568381481; bh=VKeBhnU2OZGxUtOFmDwiH/+gnCKfaZhuTAMfn4Ruuwc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Vu6VD5mCdxZZE73hnMAYr3ecNB0W7j+tDc4FfFfXHdPHI/nM+4rKE6f1jRw9WXX7P wTRyJjiOKC/6AaH+YdsvEtOkGt6duR8DhhVKxSnBk617AaLhkG3N1SWZIKCTeBYorK fCuMNWE3E3d/tulh2gagRLvVu7lir21v76BLAMiM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388745AbfIMNbR (ORCPT ); Fri, 13 Sep 2019 09:31:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:41248 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388270AbfIMNPJ (ORCPT ); Fri, 13 Sep 2019 09:15:09 -0400 Received: from localhost (unknown [104.132.45.99]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AEB0B206BB; Fri, 13 Sep 2019 13:15:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1568380507; bh=VKeBhnU2OZGxUtOFmDwiH/+gnCKfaZhuTAMfn4Ruuwc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=axUsc4X+i9SYojsR9AKEpARj5OLIoaerTTcUQSWXh6y1HKA4yjqTJL7m7PiLVZl4j vw0AInNk/c+lbZ/ZqECGpzc7DykZK8p2iTmQGzWnJebNsPIAUzixNWQALTQscqP1i4 /dEB5eE0tywRuCjzcujfTDn20QPby1dlccungX+U= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jim Mattson , Konrad Rzeszutek Wilk , Sean Christopherson , Paolo Bonzini , Sasha Levin Subject: [PATCH 4.19 087/190] KVM: VMX: Compare only a single byte for VMCS "launched" in vCPU-run Date: Fri, 13 Sep 2019 14:05:42 +0100 Message-Id: <20190913130606.517354432@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20190913130559.669563815@linuxfoundation.org> References: <20190913130559.669563815@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org [ Upstream commit 61c08aa9606d4e48a8a50639c956448a720174c3 ] The vCPU-run asm blob does a manual comparison of a VMCS' launched status 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]. Originally, 'launched' was of type 'int' and so the asm blob used 'cmpl' to check the launch status. When 'launched' was moved to be stored on a per-VMCS basis, struct vcpu_vmx's "temporary" __launched flag was added in order to avoid having to pass the current VMCS into the asm blob. The new '__launched' was defined as a 'bool' and not an 'int', but the 'cmp' instruction was not updated. 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: d462b8192368 ("KVM: VMX: Keep list of loaded VMCSs, instead of vcpus") Cc: Reviewed-by: Jim Mattson Reviewed-by: Konrad Rzeszutek Wilk Signed-off-by: Sean Christopherson Signed-off-by: Paolo Bonzini Signed-off-by: Sasha Levin --- arch/x86/kvm/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 2e310ea62d609..562f5dc4645b6 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -10808,7 +10808,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) "mov %%" _ASM_AX", %%cr2 \n\t" "3: \n\t" /* Check if vmlaunch of vmresume is needed */ - "cmpl $0, %c[launched](%0) \n\t" + "cmpb $0, %c[launched](%0) \n\t" /* Load guest registers. Don't clobber flags. */ "mov %c[rax](%0), %%" _ASM_AX " \n\t" "mov %c[rbx](%0), %%" _ASM_BX " \n\t" -- 2.20.1