From nobody Sat Nov 15 11:14:42 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1753128283078867.3883540121459; Mon, 21 Jul 2025 13:04:43 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1udwjj-0005EB-9n; Mon, 21 Jul 2025 16:03:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1udwj9-0004qC-29; Mon, 21 Jul 2025 16:03:24 -0400 Received: from isrv.corpit.ru ([212.248.84.144]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1udwj6-0004da-IG; Mon, 21 Jul 2025 16:03:10 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id E61E5139043; Mon, 21 Jul 2025 23:02:47 +0300 (MSK) Received: from think4mjt.tls.msk.ru (mjtthink.wg.tls.msk.ru [192.168.177.146]) by tsrv.corpit.ru (Postfix) with ESMTP id A32C724BECF; Mon, 21 Jul 2025 23:03:03 +0300 (MSK) From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Paolo Bonzini , Alexandre Chartre , =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= , Xiaoyao Li , Michael Tokarev Subject: [Stable-10.0.3 66/70] target/i386: do not expose ARCH_CAPABILITIES on AMD CPU Date: Mon, 21 Jul 2025 23:02:53 +0300 Message-ID: <20250721200302.133559-1-mjt@tls.msk.ru> X-Mailer: git-send-email 2.47.2 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=212.248.84.144; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1753128296054116600 From: Paolo Bonzini KVM emulates the ARCH_CAPABILITIES on x86 for both Intel and AMD cpus, although the IA32_ARCH_CAPABILITIES MSR is an Intel-specific MSR and it makes no sense to emulate it on AMD. As a consequence, VMs created on AMD with qemu -cpu host and using KVM will advertise the ARCH_CAPABILITIES feature and provide the IA32_ARCH_CAPABILITIES MSR. This can cause issues (like Windows BSOD) as the guest OS might not expect this MSR to exist on such cpus (the AMD documentation specifies that ARCH_CAPABILITIES feature and MSR are not defined on the AMD architecture). A fix was proposed in KVM code, however KVM maintainers don't want to change this behavior that exists for 6+ years and suggest changes to be done in QEMU instead. Therefore, hide the bit from "-cpu host": migration of -cpu host guests is only possible between identical host kernel and QEMU versions, therefore this is not a problematic breakage. If a future AMD machine does include the MSR, that would re-expose the Windows guest bug; but it would not be KVM/QEMU's problem at that point, as we'd be following a genuine physical CPU impl. Reported-by: Alexandre Chartre Suggested-by: Daniel P. Berrang=C3=A9 Reviewed-by: Xiaoyao Li Signed-off-by: Paolo Bonzini (cherry picked from commit d3a24134e37d57abd3e7445842cda2717f49e96d) Signed-off-by: Michael Tokarev diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 6c749d4ee8..141694f803 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -500,8 +500,12 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uin= t32_t function, * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM h= osts. * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES= is * returned by KVM_GET_MSR_INDEX_LIST. + * + * But also, because Windows does not like ARCH_CAPABILITIES on AMD + * mcahines at all, do not show the fake ARCH_CAPABILITIES MSR that + * KVM sets up. */ - if (!has_msr_arch_capabs) { + if (!has_msr_arch_capabs || !(edx & CPUID_7_0_EDX_ARCH_CAPABILITIE= S)) { ret &=3D ~CPUID_7_0_EDX_ARCH_CAPABILITIES; } } else if (function =3D=3D 7 && index =3D=3D 1 && reg =3D=3D R_EAX) { --=20 2.47.2