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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3B22ACA0FED for ; Tue, 9 Sep 2025 13:00:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uvxw5-0006BG-Si; Tue, 09 Sep 2025 08:59:01 -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 1uvrvX-0003ne-KN for qemu-devel@nongnu.org; Tue, 09 Sep 2025 02:34:03 -0400 Received: from mail-pf1-x430.google.com ([2607:f8b0:4864:20::430]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1uvrvQ-0004uR-PT for qemu-devel@nongnu.org; Tue, 09 Sep 2025 02:34:03 -0400 Received: by mail-pf1-x430.google.com with SMTP id d2e1a72fcca58-77460a64848so653340b3a.1 for ; Mon, 08 Sep 2025 23:33:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1757399622; x=1758004422; darn=nongnu.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=KlYPumXZ2GNPPhioX83eHuWYdzwsk2NeU2T6+Hb+h+o=; b=hN+5z20g8QInG14gp2lJ5e+f6QUebCgNUyw65Ydse9snreS2NPC89JJfaoMrPtciqA Ciz7TaJ2ALdMMM2XNW6G0BPRJuXA9twJPaHA8beBL9uU2fYtbaZhnYU5BpeyTorbPCkd bX5uzWj0QGvPkxCg1cZA9OIwY5E9F+dpiQDGFq/wv3t1fd1j6vXee46WtG0Gp4Bq586K 9zPBr3NzjlGAUgPR/BWK/3wubvIaMM863IDtD5SIQEAPFupK7rR7kM5EjdjYhfw6WOGX /LvofTHWddlRkRcMyxIZCfb9/xZqp/E/kZnEtVHgC5vxd0DpQF1oh18G2qaMZlyGySKk rBFw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757399622; x=1758004422; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=KlYPumXZ2GNPPhioX83eHuWYdzwsk2NeU2T6+Hb+h+o=; b=D7ZoqjXjJoQRjgYpEgt3YFJmYkeLW1TZuXS41/JINLzXPVnmANdXP0MV9kOsgY8R8W mCwZxNxuMOhd02+WA67RiLLq9meG0VT0kBiYyCN8oTKI4XNuT3X6DSlseRYioNHxqQFO NjlsIyk/nBDB9f1IHV6voh1MMYzr/f9ArVL5ha/Eht622P1PTjHsaAeUMajLXfZvmSAp m4EI9FUZ1J5AhbUl5wgVjjsseri6wvSEZ6bzAhfEpEQtdHm3/cYTpWauV53yCMTpcSHS xDZXxdYFSpjXhvyuKVDU5oKrH2ZyMZZf04Xt300egukUH2d3oQL39T3wlIxgkiERLzzB 0Ezg== X-Gm-Message-State: AOJu0YzqbLrHV+JTyTxIsffgD72aWRstibQpYBVhF/kr8k14mRkBNIIV YZHgHAP9x7w6jbRwxILRU2djbTC3gSoPYN6zBduKYyxbAiI7tn7yJTkhVbAr2olrV9Q= X-Gm-Gg: ASbGncugzJ3/29o/Gls5l1leC0VIViLokAt2N/DQKOHu3K/JvXqqzzlwcXsWr8vzoiK 7v/CoKDMCWefUEJ5Lj8jVzHMA9rrZaLhfXVkXdGG9kNZMoyVF/uTTj2EedYJ/zTvQrbcYlyIvbZ 4ZSSpA+AZqvNxDmXntT8YowYoLAuVNlvUyJGkCxOl7pBqVziWzqYc9tA/wmHJrG29B2/w+83zv4 Ha8LUvWrvJ7iPylbS6g3WwrtRO52wi8Y6NNrZqsrjbwk7fwoNTxzBI5RNYgVGzfQcfyiBU1g/jZ 8CXZWM0iW+c8giZ7aCDbFs78uGH178aAfMi0+UlGDamFpS4sJi2OsPpGx5dBjuBoL0YykaOW3++ xZHKhAkKoEBbGs+nV6Jyc0zzJitIe4km7QT03UqR8h2ZPR6Ngcqm77mRX4BjXvg== X-Google-Smtp-Source: AGHT+IG5VjYQNMdw/MpShOmZhgIpumMJ2z8imKGQ/mFwUjSsWb6PA2uPoGsX+egsKKVRJhRC4n1lfQ== X-Received: by 2002:a05:6a20:9392:b0:24e:2cee:9592 with SMTP id adf61e73a8af0-2534547a6c6mr15549901637.46.1757399621653; Mon, 08 Sep 2025 23:33:41 -0700 (PDT) Received: from localhost.localdomain ([61.213.176.12]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b5235c0c3e2sm4213501a12.20.2025.09.08.23.33.38 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 08 Sep 2025 23:33:41 -0700 (PDT) From: Fei Li To: pbonzini@redhat.com, mtosatti@redhat.com, seanjc@google.com, kvm@vger.kernel.org Cc: qemu-devel@nongnu.org, Fei Li Subject: [PATCH] KVM: x86: Restrict writeback of SMI VCPU state Date: Tue, 9 Sep 2025 14:33:27 +0800 Message-Id: <20250909063327.14263-1-lifei.shirley@bytedance.com> X-Mailer: git-send-email 2.39.2 (Apple Git-143) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::430; envelope-from=lifei.shirley@bytedance.com; helo=mail-pf1-x430.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-Mailman-Approved-At: Tue, 09 Sep 2025 08:58:42 -0400 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Recently, we meet a SMI race bug triggered by one monitor tool in our production environment. This monitor executes 'info registers -a' hmp at a fixed frequency, even during VM startup process, which makes some AP stay in KVM_MP_STATE_UNINITIALIZED forever, thus VM hangs. The complete calling processes for the SMI race are as follows: //thread1 //thread2 //thread3 `info registers -a` hmp [1] AP(vcpu1) thread [2] BSP(vcpu0) send INIT/SIPI [3] [2] KVM: KVM_RUN and then schedule() in kvm_vcpu_block() loop [1] for each cpu: cpu_synchronize_state if !qemu_thread_is_self() 1. insert to cpu->work_list, and handle asynchronously 2. then kick the AP(vcpu1) by sending SIG_IPI/SIGUSR1 signal [2] KVM: checks signal_pending, breaks loop and returns -EINTR Qemu: break kvm_cpu_exec loop, run 1. qemu_wait_io_event() => process_queued_cpu_work => cpu->work_list.func() e.i. do_kvm_cpu_synchronize_state() callback => kvm_arch_get_registers => kvm_get_mp_state /* KVM: get_mpstate also calls kvm_apic_accept_events() to handle INIT and SIPI */ => cpu->vcpu_dirty = true; // end of qemu_wait_io_event [3] SeaBIOS: BSP enters non-root mode and runs reset_vector() in SeaBIOS. send INIT and then SIPI by writing APIC_ICR during smp_scan KVM: BSP(vcpu0) exits, then => handle_apic_write => kvm_lapic_reg_write => kvm_apic_send_ipi to all APs => for each AP: __apic_accept_irq, e.g. for AP(vcpu1) ==> case APIC_DM_INIT: apic->pending_events = (1UL << KVM_APIC_INIT) (not kick the AP yet) ==> case APIC_DM_STARTUP: set_bit(KVM_APIC_SIPI, &apic->pending_events) (not kick the AP yet) [2] Qemu continue: 2. kvm_cpu_exec() => if (cpu->vcpu_dirty): => kvm_arch_put_registers => kvm_put_vcpu_events KVM: kvm_vcpu_ioctl_x86_set_vcpu_events => clear_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events); e.i. pending_events changes from 11b to 10b // end of kvm_vcpu_ioctl_x86_set_vcpu_events Qemu: => after put_registers, cpu->vcpu_dirty = false; => kvm_vcpu_ioctl(cpu, KVM_RUN, 0) KVM: KVM_RUN => schedule() in kvm_vcpu_block() until Qemu's next SIG_IPI/SIGUSR1 signal /* But AP(vcpu1)'s mp_state will never change from KVM_MP_STATE_UNINITIALIZED to KVM_MP_STATE_INIT_RECEIVED, even then to KVM_MP_STATE_RUNNABLE without handling INIT inside kvm_apic_accept_events(), considering BSP will never send INIT/SIPI again during smp_scan. Then AP(vcpu1) will never enter non-root mode */ [3] SeaBIOS: waits CountCPUs == expected_cpus_count and loops forever e.i. the AP(vcpu1) stays: EIP=0000fff0 && CS =f000 ffff0000 and BSP(vcpu0) appears 100% utilized as it is in a while loop. To fix this, avoid clobbering SMI when not putting "reset" state, just like NMI abd SIPI does. Signed-off-by: Fei Li --- target/i386/kvm/kvm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 369626f8c8..598661799a 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -5056,7 +5056,7 @@ static int kvm_put_vcpu_events(X86CPU *cpu, int level) events.sipi_vector = env->sipi_vector; - if (has_msr_smbase) { + if (has_msr_smbase && level >= KVM_PUT_RESET_STATE) { events.flags |= KVM_VCPUEVENT_VALID_SMM; events.smi.smm = !!(env->hflags & HF_SMM_MASK); events.smi.smm_inside_nmi = !!(env->hflags2 & HF2_SMM_INSIDE_NMI_MASK); -- 2.39.2 (Apple Git-143)