From nobody Tue Sep 23 22:10:00 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 1752746540879263.87232308145997; Thu, 17 Jul 2025 03:02:20 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ucLK9-0006Cn-HW; Thu, 17 Jul 2025 05:54:46 -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 1ucL2K-0003jH-Jr; Thu, 17 Jul 2025 05:36:20 -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 1ucL2I-000281-9g; Thu, 17 Jul 2025 05:36:20 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id D16B4137D00; Thu, 17 Jul 2025 12:34:05 +0300 (MSK) Received: from think4mjt.origo (mjtthink.wg.tls.msk.ru [192.168.177.146]) by tsrv.corpit.ru (Postfix) with ESMTP id B32B92491F9; Thu, 17 Jul 2025 12:34:13 +0300 (MSK) From: Michael Tokarev To: qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org, Michael Tokarev , Xiaoyao Li , Qian Wen , Zhao Liu , Paolo Bonzini Subject: [Stable-10.0.3 63/65] i386/cpu: Fix cpu number overflow in CPUID.01H.EBX[23:16] Date: Thu, 17 Jul 2025 12:33:59 +0300 Message-ID: <20250717093412.728292-24-mjt@tls.msk.ru> X-Mailer: git-send-email 2.47.2 In-Reply-To: References: MIME-Version: 1.0 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: 1752746541444116600 Content-Type: text/plain; charset="utf-8" The legacy topology enumerated by CPUID.1.EBX[23:16] is defined in SDM Vol2: Bits 23-16: Maximum number of addressable IDs for logical processors in this physical package. When threads_per_socket > 255, it will 1) overwrite bits[31:24] which is apic_id, 2) bits [23:16] get truncated. Specifically, if launching the VM with -smp 256, the value written to EBX[23:16] is 0 because of data overflow. If the guest only supports legacy topology, without V2 Extended Topology enumerated by CPUID.0x1f or Extended Topology enumerated by CPUID.0x0b to support over 255 CPUs, the return of the kernel invoking cpu_smt_allowed() is false and APs (application processors) will fail to bring up. Then only CPU 0 is online, and others are offline. For example, launch VM via: qemu-system-x86_64 -M q35,accel=3Dkvm,kernel-irqchip=3Dsplit \ -cpu qemu64,cpuid-0xb=3Doff -smp 256 -m 32G \ -drive file=3Dguest.img,if=3Dnone,id=3Dvirtio-disk0,format=3Draw \ -device virtio-blk-pci,drive=3Dvirtio-disk0,bootindex=3D1 --nographic The guest shows: CPU(s): 256 On-line CPU(s) list: 0 Off-line CPU(s) list: 1-255 To avoid this issue caused by overflow, limit the max value written to EBX[23:16] to 255 as the HW does. Cc: qemu-stable@nongnu.org Reviewed-by: Xiaoyao Li Signed-off-by: Qian Wen Signed-off-by: Zhao Liu Link: https://lore.kernel.org/r/20250714080859.1960104-6-zhao1.liu@intel.com Signed-off-by: Paolo Bonzini (cherry picked from commit a62fef58299562aae6667b8d8552247423e886b3) (Mjt: fixup for 10.0.x series due to missing v10.0.0-2217-gf985a1195b "i386/cpu: Fix number of addressable IDs field for CPUID.01H.EBX[23:16]") Signed-off-by: Michael Tokarev diff --git a/target/i386/cpu.c b/target/i386/cpu.c index 2c9517f56d..4603b2b98b 100644 --- a/target/i386/cpu.c +++ b/target/i386/cpu.c @@ -6828,7 +6828,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, = uint32_t count, } *edx =3D env->features[FEAT_1_EDX]; if (threads_per_pkg > 1) { - *ebx |=3D threads_per_pkg << 16; + /* Fixup overflow: max value for bits 23-16 is 255. */ + *ebx |=3D MIN(threads_per_pkg, 255) << 16; } if (!cpu->enable_pmu) { *ecx &=3D ~CPUID_EXT_PDCM; --=20 2.47.2